A method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source

Abstract

The present invention provides a method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source. In the method for preparing the silicon-carbon composite material, a CO2 reduction catalyst is used. The CO2 reduction catalyst is MFe2O4, where M is one of Mg, Ni, and Cu, and has the characteristics of being easy to remove, efficient, and easy to mix. The silicon-carbon composite material is obtained by high-temperature reduction of CO2 with 0.5-3% by mass of MFe2O4 and nano-silicon. The silicon-carbon composite material has an in-situ generated carbon coating layer and a silicon oxide layer resistant to electrolyte erosion, and has advantages such as a higher first charge capacity than the original silicon powder, a high Coulombic efficiency, and high cycle stability. The electrochemical performance is greatly improved. While greenly reducing CO2, a high-performance silicon-carbon anode material is obtained, which has broad market application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of anode materials for lithium-ion batteries. Specifically, a method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source is provided. Technical Background

[0002] With the continuous development of industry in today's society, the concentration of CO2 in the atmosphere has been continuously rising, and the greenhouse effect caused by this has seriously affected the sustainable development of humanity. Therefore, the efficient utilization of CO2 has become a key point. At the same time, the development of clean and sustainable new energy has also become the focus of people's attention. Therefore, it is even more important to efficiently utilize CO2 in new energy. Currently, most of the catalytic reduction of CO2 is carried out by chemical methods, biological methods, photochemical methods, and electrochemical methods, and finally CO2 is reduced to CO, C2H4, etc. The reduction rate of CO2 by the biological reduction method is too low to meet the current requirements. Generally, the commonly used catalyst types in the electrochemical method include transition metal elements and their oxide catalysts, transition metal sulfide metal-organic frameworks (MOF), covalent organic compounds (COF), heteroatom-doped carbon-based catalysts, and metal-nitrogen-carbon catalysts (M-N-C). Although the electrochemical reduction method can utilize CO2, its reduction cost is high and the added value of the reduction products is not high, making it difficult to bring economic benefits. Therefore, it is not suitable for large-scale use.

[0003] Patent Application No. 202210710705.7 proposed a nano gold-palladium alloy catalyst. Its preparation process is to carry out reduction and coprecipitation reactions on a mixed solution containing a gold precursor, a palladium precursor, a reducing agent, and a stabilizer under a protective atmosphere. The reaction product is washed, dried, and then calcined to finally obtain the catalyst. Since this catalyst is synthesized by the coprecipitation method, the preparation cycle is long, and the use of precious metals to prepare the catalyst leads to an increase in the cost of the catalyst, resulting in too high a cost during the CO2 catalytic process.

[0004] Because silicon has advantages such as a high specific capacity, a low lithium insertion / extraction potential, and rich resources, it has been widely studied and applied in lithium-ion batteries. However, since silicon itself is a semiconductor and there is a large volume expansion during charge and discharge, solving the conductivity problem and the expansion problem is of utmost importance in applications. Using silicon-carbon composites has become a very good solution. Among the use of various carbon sources, using CO2 as a carbon source is very economical, safe, and environmentally friendly.

[0005] Due to the various drawbacks of the above-mentioned CO2 reduction methods and catalysts and the advantages of CO2 as a carbon source in the preparation of silicon-carbon composites, it is particularly important to develop an efficient, environmentally friendly and economical CO2 catalyst for the preparation of silicon-carbon composites. The present invention proposes an efficient CO2 catalyst that directly reduces CO2 to C and uses it in the preparation of the negative electrode material of a lithium-ion battery, which not only improves the added value of the CO2 reduction product but also is more environmentally friendly. Summary of the Invention

[0006] To solve the above deficiencies, the present invention innovatively proposes a preparation method that directly uses CO2 as a carbon source in the production of silicon-carbon composites.

[0007] On the one hand, the present invention provides a method for efficiently preparing silicon-carbon composites using CO2 as a carbon source. The CO2 reduction catalyst is MFe2O4, where M is one of Mg, Ni, and Cu.

[0008] The method for efficiently preparing silicon-carbon composites using CO2 as a carbon source provided by the present invention includes the following steps:

[0009] Weigh the metal salts of iron and M according to the stoichiometric ratio, ball mill them in a ball mill for 4 h to fully mix, then add a certain amount of citric acid to prepare a solution. Take the solution and place it in a spray pyrolysis furnace at 600 °C to make it fully combust and decompose, and keep it warm for 30 minutes; after cooling, collect the combustion product, ball mill it and pass it through a 200-mesh sieve to obtain the CO2 nano-reduction catalyst.

[0010] Preferably, in the above step, the metal salts of iron and M are nitrates or acetates.

[0011] Preferably, in the above step, the mass of the citric acid is 1.2 - 1.8 times the theoretical stoichiometric ratio.

[0012] On the other hand, the present invention provides a method for preparing silicon-carbon composites using CO2 as a carbon source, which is characterized by including the following steps: ball mill and mix the catalyst and nano-silicon powder in a certain proportion, then put it into a high-temperature furnace with a CO2 atmosphere for reduction, and the heating rate is 2 °C / min. Then cool it with the furnace. After cooling, pickle the material with 2 mol / L hydrochloric acid, filter it by suction, and dry it to obtain the silicon-carbon composite material.

[0013] Preferably, in the above step, the mass ratio of the catalyst to the nano-silicon powder is 0.5 - 3%.

[0014] Preferably, in the above step, the temperature of the atmosphere furnace is 700 - 900 °C, and the time is 2 - 6 h.

[0015] Compared with the prior art, the outstanding benefits of the present invention are:

[0016] (1) The present invention innovatively proposes a method for preparing a nano-level CO2 reduction catalyst material by spray combustion. This process is simple and fast, and the catalyst material has the characteristics of being easily removed, highly efficient, and easily mixed.

[0017] (2) For the CO2 reduction catalyst described in the present invention, the number of oxygen vacancies in the material can be controlled by adding different amounts of citric acid, thereby controlling the decomposition rate of CO2 by the catalyst and the amount of CO2 decomposed to meet different requirements.

[0018] (3) The CO2 catalyst doped in nano-silicon proposed by the present invention can in-situ reduce a carbon coating layer on the silicon surface, thereby preparing a highly conductive silicon-carbon composite material, which greatly increases the added value of the CO2 reduction product.

[0019] (4) The CO2 catalyst doped in nano-silicon proposed by the present invention can also construct a layer of silicon oxide on the silicon surface by using highly active oxygen during the reduction process, thereby further improving the electrochemical performance of the silicon-carbon composite material. Description of the Drawings

[0020] Figure 1 It is the X-ray diffraction pattern of the silicon-carbon composite material in Example 1 of the present invention.

[0021] Figure 2 It is the scanning electron microscope image of the silicon-carbon composite material in Example 1 of the present invention.

[0022] Figure 3 It is the first charge-discharge curve of the silicon-carbon composite material and the original silicon powder in Example 1 of the present invention.

[0023] Figure 4 It is the 100-cycle curve of the silicon-carbon composite material and the original silicon powder in Example 1 of the present invention. Detailed Embodiments

[0024] In order to further illustrate the present invention, the following describes in detail a method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source provided by the present invention in combination with embodiments.

[0025] Example 1

[0026] Prepare the CO2 reduction catalyst MgFe2O4 according to the following steps and use it to prepare a silicon-carbon composite material

[0027] Weigh ferric acetate and magnesium acetate respectively according to a molar ratio of 2:1, and ball-mill them in a ball mill for 4 h to fully mix ferric acetate and magnesium acetate. Then add citric acid at 1.2 times the stoichiometric ratio, and stir well to prepare a solution with a metal ion concentration of 0.2 mol / L. Take the solution and place it in a spray pyrolysis furnace at 600 °C to make it fully combust and decompose. After the flame goes out, keep it warm for 30 minutes; after cooling, collect the combustion product, ball-mill it, and pass it through a 200-mesh sieve to obtain the product MgFe2O4. Weigh 0.5 g of MgFe2O4 and add it to 100 g of nano-silicon powder, ball-mill for 2 h to make MgFe2O4 and nano-silicon powder evenly mixed, and then put it into a high-temperature furnace with a CO2 atmosphere for reduction. The temperature is 700 °C, the time is 6 h, and the heating rate is 2 °C / min. Then cool it with the furnace. After cooling, pickle the material with 2 mol / L hydrochloric acid, filter it by suction, and then dry it in a blast drying oven at 80 °C for 2 h. After drying, obtain the silicon-carbon composite material.

[0028] The XRD of the material is as Figure 1 shown. It can be seen that after catalytic reduction by MgFe2O4, it does not affect the silicon itself. The incorporated MgFe2O4 is eluted by hydrochloric acid, and it can be seen that there is a broad peak near 20°, which is the amorphous carbon peak obtained by CO2 reduction, indicating that this method can deposit a layer of conductive carbon on the surface of nano-silicon well with CO2 as the carbon source. The SEM characterization is as Figure 2 shown, and it can be seen that the material still maintains the nano-material configuration after being compounded.

[0029] Example 2

[0030] Prepare the CO2 reduction catalyst NiFe2O4 according to the following steps and use it to prepare the silicon-carbon composite material

[0031] Weigh ferric nitrate and nickel nitrate respectively according to a molar ratio of 2:1, and ball-mill them in a ball mill for 4 h to fully mix ferric nitrate and nickel nitrate. Then add citric acid at 1.5 times the stoichiometric ratio, and stir well to prepare a solution with a metal ion concentration of 0.2 mol / L. Take the solution and place it in a spray pyrolysis furnace at 600 °C to make it fully combust and decompose. After the flame goes out, keep it warm for 30 minutes; after cooling, collect the combustion product, ball-mill it, and pass it through a 200-mesh sieve to obtain the product NiFe2O4. Weigh 1.5 g of NiFe2O4 and add it to 100 g of nano-silicon powder, ball-mill for 2 h to make NiFe2O4 and nano-silicon powder evenly mixed, and then put it into a high-temperature furnace with a CO2 atmosphere for reduction. The temperature is 800 °C, the time is 4 h, and the heating rate is 2 °C / min. Then cool it with the furnace. After cooling, pickle the material with 2 mol / L hydrochloric acid, then dry it in a blast drying oven at 80 °C for 2 h, filter it by suction, and then dry it in a blast drying oven at 80 °C for 2 h. After drying, obtain the silicon-carbon composite material.

[0032] Example 3

[0033] Prepare the CO2 reduction catalyst CuFe2O4 according to the following steps and use it to prepare a silicon-carbon composite material

[0034] Weigh ferric nitrate and copper nitrate respectively according to a molar ratio of 2:1, and ball-mill them in a ball mill for 4 h to fully mix ferric nitrate and copper nitrate. Then add citric acid 1.8 times the stoichiometric ratio, and stir well to prepare a solution with a metal ion concentration of 0.2 mol / L. Take the solution and place it in a spray pyrolysis furnace at 600 °C to make it fully combust and decompose. After the flame goes out, keep it warm for 30 minutes; after cooling, collect the combustion product, ball-mill it and pass it through a 200-mesh sieve to obtain the product CuFe2O4. Weigh 3 g of CuFe2O4 and add it to 100 g of nano-silicon powder, ball-mill for 2 h to mix CuFe2O4 and nano-silicon powder evenly, and then put it into a high-temperature furnace with a CO2 atmosphere for reduction. The temperature is 900 °C, the time is 2 h, and the heating rate is 2 °C / min. Then cool it with the furnace. After cooling, pickle the material with 2 mol / L hydrochloric acid, filter it by suction, and then dry it in a blast drying oven at 80 °C for 2 h to obtain the silicon-carbon composite material after drying.

[0035] Performance test

[0036] Make electrode sheets from the silicon-carbon composite materials obtained in Examples 1-3 and the original materials without carbon coating according to the silicon-carbon negative electrode material standard and assemble them into coin cells for performance testing. The test data are shown in Table 1.

[0037] Table 1

[0038] Example Example 1 Example 2 Example 3 Original silicon powder Initial 0.1C charge specific capacity (mAh / g) 2901.2 2870.4 2930.7 2461.3 Initial 0.1C discharge specific capacity (mAh / g) 3330.8 3286.2 3180.5 3168.1 Initial charge-discharge efficiency 87.10％ 87.34％ 92.15％ 77.69％ 100-cycle capacity retention rate (1C) 74.86％ 76.63％ 75.58％ 28.53％

[0039] The first charge-discharge curves of the silicon-carbon composite material obtained in Example 1 and the original silicon powder are as Figure 3 shown, and the 100-cycle curves are as Figure 4 shown. The results show that for the first 0.1C cycle, the charge specific capacity of the material is 2901.2 mAh / g, the discharge specific capacity is 3330.8 mAh / g, and the first charge-discharge efficiency is 87.10%. Compared with the original silicon powder, it is increased by 439.9 mAh / g, 162.7 mAh / g, and 9.41% respectively. The 100-cycle capacity retention rate of Example 1 is 74.86%, which is much higher than 28.53% of the original silicon powder. Because of the poor conductivity and weak resistance to electrolyte erosion of the original silicon powder, it is very easy to fail and deactivate in high-current cycling, resulting in extremely fast capacity decay. The first charge-discharge specific capacities, efficiencies, and 100-cycle capacity retention rates of Example 2 and Example 3 are all greatly improved compared with the original silicon powder. It shows that the prepared CO2 reduction catalyst can efficiently catalyze the reduction of CO2, effectively form a conductive carbon coating layer and an anti-corrosion oxide layer on the surface of nano-silicon, which not only improves the first Coulomb efficiency of the material, but also greatly improves the cycling performance of the material.

[0040] The above-described cases are only preferred implementation cases of the present invention and are not used to limit this application. The preparation method of the present invention is simple to operate. The prepared CO2 reduction catalyst can be directly applied to the preparation of silicon-carbon anode materials. Its preparation cost is low, the catalysis is efficient, and the added value of the product is high. For those skilled in the art, without departing from the principle of the present invention, various changes and modifications can be made to this application. Any modifications, substitutions, improvements, etc. should be included within the protection scope of this application.

Claims

1. A method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source, characterized in that, In the method for preparing the silicon-carbon composite material, a CO2 nano-reduction catalyst is used. The CO2 nano-reduction catalyst is MFe2O4, where M is one of Mg, Ni, and Cu, and the method includes the following steps: S1: Weigh the metal salts of iron and M according to the stoichiometric ratio, ball-mill them in a ball mill for 4 h to fully mix, then add citric acid to prepare a solution. Take the solution and place it in a spray pyrolysis furnace at 600 °C to allow it to fully combust and decompose, and keep the temperature for 30 minutes. After cooling, collect the combustion product, ball-mill it and pass it through a 200-mesh sieve to obtain the CO2 nano-reduction catalyst; S2: Ball-mill and mix the catalyst and nano-silicon powder in a certain proportion, then put it into a high-temperature furnace with a CO2 atmosphere for reduction. The heating rate is 2 °C / min, and then it is cooled with the furnace. After cooling, pickle the material with 2 mol / L hydrochloric acid, filter by suction, and dry to obtain the silicon-carbon composite material; In the step S1 described above, the mass of citric acid is 1.2 - 1.8 times the theoretical stoichiometric ratio; In the step S2 described above, the temperature of the atmosphere furnace is 700 - 900 °C, and the time is 2 - 6 h.

2. The method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source according to claim 1, characterized in that, In the step S1 described above, the metal salts of iron and M are nitrates or acetates.

3. The method for efficiently preparing a silicon-carbon composite material using CO2 as a carbon source according to claim 1, characterized in that, In the step S2 described above, the mass ratio of the catalyst to the nano-silicon powder is 0.5 - 3%.

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