Preparation method and application of three-dimensional porous silicon-carbon composite aerogel

Abstract

The invention relates to a preparation method and application of three-dimensional porous silicon-carbon composite aerogel. The preparation method comprises the following steps: dissolving a coupling agent in an organic solvent, and uniformly stirring; adding an organosilane coupling agent and water, and stirring to uniformly disperse the organosilane coupling agent and the water; adding an acidic aqueous solution to adjust the pH value for the first time, and hydrolyzing to form sol; then adding a conductive substance, then adding an alkaline aqueous solution to adjust the pH value for the second time, and reacting to obtain wet gel; soaking the wet gel in an ethanol solution, then taking out the wet gel, soaking the wet gel in a hydrophobic modifier, and drying after modification is completed to obtain the three-dimensional porous silicon-carbon composite aerogel. According to the invention, the skeleton strength can be effectively enhanced, hydrophobicity is endowed, and the aerogel has the characteristics of high specific surface area, strong mechanical property and functionalization, so that the air electrode can realize considerable capacity and longer cycle life; the preparation method is high in preparation efficiency, low in cost and suitable for large-scale industrial production, and the aging time can be effectively shortened to be within 5 h.

Description

Technical Field

[0001] The present invention relates to the technical field of metal-air batteries, and particularly relates to a preparation method and application of a three-dimensional porous silicon-carbon composite aerogel. Background Art

[0002] At present, the energy crisis and global warming have become hot social issues that people are deeply concerned about. In the current context, it is an urgent need for global sustainable development to achieve efficient and economically feasible alternative energy conversion and storage devices. Metal-air batteries, with their high specific capacity and environmentally friendly characteristics, show great application potential in the energy storage field. Compared with lithium-ion batteries, their energy density is 5 to 10 times higher, with a higher theoretical energy density and safety performance. The working principle of metal-air batteries is based on the redox reaction of oxygen molecules in the atmosphere, which means that most of the oxygen required by the battery comes from the surrounding air, not only reducing production costs but also increasing the energy density of the battery and significantly reducing the weight of the battery. Developing metal-air batteries that can meet the requirements of electrified transportation and high-energy-density energy storage has become the research focus. However, at present, due to reasons such as the escape of metal salt solutions from the negative electrode region and corrosion caused by concentration polarization in metal-air batteries, the cycle stability of the batteries is reduced, and the charge-discharge efficiency is poor.

[0003] To solve the above problems, "A Carbon-Doped Silica Aerogel Air Electrode and Preparation Method" provides the following technical solutions, including the following steps: stirring a chemical additive and deionized water evenly to obtain a mixed solution I; adding an organosilane coupling agent and an organic solvent to the mixed solution I to obtain a mixed solution II; adding an acidic aqueous solution to the mixed solution II for the first time to adjust the pH value to obtain a silica hydrosol; then adding a conductive substance, and then adding a basic aqueous solution to adjust the pH value for the second time to obtain a silica gel; soaking the silica gel in a solution III composed of a low surface tension organic solvent and ethanol in a compound, and then taking out the silica gel and soaking it in a hydrophobic modifier for modification, and drying after the modification is completed to obtain a carbon-doped silica aerogel, which is used to further prepare an air electrode. The existing problems are: this method uses chemical additives such as formamide, acetamide, N, N-dimethylformamide, polyethylene glycol, and glycerol, and the solvent system is toxic. The compound solution used will cause aggregation of the precursors, and the structure has defects, which affects the pore structure and mechanical properties of the final aerogel. Moreover, the number of pores in the obtained aerogel is relatively limited, so it has problems such as low specific surface area, few pores, and unsatisfactory electronic conductivity. At the same time, the function is single, resulting in problems such as insufficient stability, low cycle performance, and weak oxygen reduction reaction activity of the prepared air electrode. Therefore, it is urgent to prepare a three-dimensional carbon-coated silica aerogel with a high specific surface area, many pores, and excellent electronic conductivity to further prepare an efficient and reversible air electrode. Summary of the Invention

[0004] The present invention provides a preparation method and application of a three-dimensional porous silicon-carbon composite aerogel material to solve the problems existing in the prior art, that is, the structure has defects, which affects the pore structure and mechanical properties of the final aerogel, and the number of pores in the obtained aerogel is relatively limited. Therefore, it has a low specific surface area, few pores, and unsatisfactory electronic conductivity. At the same time, the function is single, resulting in low stability, poor cycle efficiency, and low oxygen reduction activity of the prepared air electrode.

[0005] To achieve the above object, the present invention adopts the following technical solutions: A preparation method of a three-dimensional porous silicon-carbon composite aerogel, comprising the following steps:

[0006] Step 1: Dissolve a coupling agent in an organic solvent, mix and stir evenly to obtain a mixed solution I;

[0007] Step 2: Add an organosilane coupling agent and water to the mixed solution I, and stir to make it evenly dispersed in the solution to obtain a mixed solution II;

[0008] Step 3: Add an acidic aqueous solution to the mixed solution II to adjust the pH value for the first time to make it fully hydrolyzed to form a sol; then add a conductive substance, and then add a basic aqueous solution to adjust the pH value for the second time. Pour the sol into the inner lining of a hydrothermal kettle and place it in an oven to react for a certain time to obtain a wet gel;

[0009] Step 4: Immerse the wet gel in an ethanol solution, then take out the wet gel and immerse it in a hydrophobic modifier for modification. After the modification is completed, dry it to obtain a three-dimensional porous silicon-carbon composite aerogel.

[0010] Further, in the above step 1, the coupling agent is γ-methacryloxypropyltrimethoxysilane, and the addition amount is 1%-5% of the total mass of the mixed solution I; the organic solvent is ethanol.

[0011] Further, in the above step 2, the molar ratio of the organosilane coupling agent to water is (3-5):1; the organosilane coupling agent is tetraethyl orthosilicate or tetrabutyl orthosilicate.

[0012] Further, in the above step 3, the first pH value adjustment is 2-3, and the concentration of the acidic aqueous solution is 0.1-0.2 mol / L; the second pH value adjustment is 6-7; the concentration of the basic aqueous solution is 0.1-0.2 mol / L.

[0013] Further, in the above step 3, the reaction temperature in the oven is 40-80°C, the aging temperature is 120-160°C, and the reaction time is 100-200 min.

[0014] Further, an application of a three-dimensional porous silicon-carbon composite aerogel prepared by the above preparation method in the preparation of an air electrode.

[0015] Compared with the prior art, the present invention has the following beneficial effects:

[0016] 1. In the preparation method provided by the present invention, KH570 coupling agent is used, which is non-toxic, ensuring the safety of production. At the same time, it supports atmospheric drying and through chemical bonding, it can effectively enhance the framework strength and impart hydrophobicity, making the aerogel have both high specific surface area, strong mechanical properties and functionalization characteristics.

[0017] 2. The present invention uses an ethanol solution to dissolve the coupling agent. Ethanol has a similar polarity to the silica precursor, which can effectively disperse the hydrolysis products and form a uniform sol at the same time. While using a compound solution may cause the aggregation of the precursor, affecting the pore structure and mechanical properties of the final aerogel. Commonly used silane coupling agents have a high solubility in ethanol and can be uniformly grafted onto the silica framework, improving the modification efficiency.

[0018] 3. The preparation method of the present invention has high preparation efficiency. Tetraethyl orthosilicate (TEOS) is used as the precursor to synthesize silica aerogel (SA) by sol-gel method. The hydrothermal method is adopted to carry out the aging process in a high-temperature and high-pressure closed environment instead of the conventional aging method, which can effectively shorten the aging time to within 5 hours.

[0019] 4. The three-dimensional porous silicon-carbon composite aerogel air electrode provided by the present invention has excellent high specific surface area, high porosity and excellent conductivity. When the electrocatalyst is uniformly distributed on the three-dimensional porous carbon, the contact area with the electrolyte is enlarged, thereby significantly improving the catalytic performance. Growing carbon materials in situ in the SA system can successfully combine SiO2 with abundant carbonaceous materials. The air electrode prepared by using the composite aerogel of the present invention not only provides a fast transmission path for electrons by reducing the active particle size, but also provides higher stability and higher oxygen reduction activity, so that the air electrode can achieve considerable capacity and longer cycle life.

[0020] 5. The composite aerogel prepared by the preparation method of the present invention has the characteristics of controllable structure and adjustable pore size, and the nano-micropores with high porosity can effectively accommodate more electrolyte. The carbon materials are uniformly grown in the silica aerogel framework structure by sol-gel method, and the KH570 coupling agent is used to reduce the generation of cluster phenomena, realizing the preparation of three-dimensional carbon materials with high content, high void and low density. The prepared composite aerogel replaces the traditional one-dimensional electrode material as the air electrode positive material. Graphite and conductive carbon materials are uniformly dispersed in the three-dimensional interconnected porous network structure of silica aerogel, reducing the cost required for preparation and being suitable for large-scale industrial production. Brief Description of the Drawings

[0021] Figure 1 This is the scanning electron microscope image of the three-dimensional porous silicon-carbon composite aerogel air electrode with a magnification of 35.0k in Example 1 of the present invention.

[0022] Figure 2 This is the scanning electron microscope image of the three-dimensional porous silicon-carbon composite aerogel air electrode with a magnification of 60.0k in Example 1 of the present invention. Detailed implementation manners

[0023] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention.

[0024] In the following examples, various raw materials are used, unless otherwise specified, all using conventional commercially available products.

[0025] Example 1, A preparation method of a three-dimensional porous silicon-carbon composite aerogel, comprising the following steps:

[0026] Step 1: Dissolve KH570 with an addition amount of 5% in 11.5 g of ethanol solution and stir for 30 min;

[0027] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue to stir to make it evenly dispersed.

[0028] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution, adjust the pH to 2 for the first time, and then continue to stir to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are evenly mixed and mix them evenly. While stirring, slowly add NH3·H2O to adjust the pH to 7, then pour the sol into the inner liner of the hydrothermal reactor, place it in an oven at 60 °C and react for 150 min, and then adjust the oven to 140 °C to age it to form a wet gel.

[0029] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h, and then prepare a hydrophobic modifier solution by adding 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane. Immerse the obtained gel in it for hydrophobic modification, and perform atmospheric vacuum drying for 12 h to obtain a carbon-doped silica aerogel.

[0030] Example 2, A preparation method of a three-dimensional porous silicon-carbon composite aerogel, comprising the following steps:

[0031] Step 1: Dissolve KH570 with an addition amount of 1% in 11.5 g of ethanol solution and stir for 30 min.

[0032] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue to stir to make it evenly dispersed.

[0033] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 2 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are evenly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 7. Then pour the sol into the inner lining of the hydrothermal reactor, place it in an oven at 80 °C and react for 150 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0034] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution. Immerse the obtained gel in it for hydrophobic modification. After drying under normal pressure and vacuum for 12 h, carbon-doped silica aerogel is obtained.

[0035] Example 3. A preparation method of a three-dimensional porous silicon-carbon composite aerogel, comprising the following steps:

[0036] Step 1: Dissolve KH570 with an addition amount of 5% in 11.5 g of ethanol solution and stir for 30 min,

[0037] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue stirring to make it evenly dispersed,

[0038] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 3 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are evenly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 7. Then pour the sol into the inner lining of the hydrothermal reactor, place it in an oven at 40 °C and react for 160 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0039] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution. Immerse the obtained gel in it for hydrophobic modification. After drying under normal pressure and vacuum for 12 h, carbon-doped silica aerogel is obtained.

[0040] Example 4. A preparation method of a three-dimensional porous silicon-carbon composite aerogel, comprising the following steps:

[0041] Step 1: Dissolve KH570 with an addition amount of 5% in 11.5 g of ethanol solution and stir for 30 min,

[0042] Step 2: Add 52 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue stirring to make it evenly dispersed,

[0043] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 2 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are evenly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 7, then pour the sol into the inner lining of the hydrothermal reactor, place it in an oven at 60 °C and react for 150 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0044] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution, immerse the obtained gel in it for hydrophobic modification, and obtain a carbon-doped silica aerogel after drying under normal pressure and vacuum for 12 h.

[0045] Example 5. A preparation method of a three-dimensional porous silicon-carbon composite aerogel includes the following steps:

[0046] Step 1: Dissolve KH570 with an addition amount of 5% in 23 g of ethanol solution and stir for 30 min,

[0047] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue stirring to make them evenly dispersed,

[0048] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 2 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are evenly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 6, then pour the sol into the inner lining of the hydrothermal reactor, place it in an oven at 60 °C and react for 120 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0049] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution, immerse the obtained gel in it for hydrophobic modification, and obtain a carbon-doped silica aerogel after drying under normal pressure and vacuum for 12 h.

[0050] Example 6. A preparation method of a three-dimensional porous silicon-carbon composite aerogel includes the following steps:

[0051] Step 1: Dissolve KH570 with an addition amount of 5% in 11.5 g of ethanol solution and stir for 30 min,

[0052] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue stirring to make them evenly dispersed,

[0053] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 3 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 5 g of graphite and 2 g of conductive carbon that are uniformly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 7. Then pour the sol into the inner lining of the hydrothermal autoclave, place it in an oven at 40 °C and react for 150 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0054] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution, and immerse the obtained gel in it for hydrophobic modification. After drying under normal pressure and vacuum for 12 h, a carbon-doped silica aerogel is obtained.

[0055] Example 7. A method for preparing a three-dimensional porous silicon-carbon composite aerogel includes the following steps:

[0056] Step 1: Dissolve KH570 with an addition amount of 5% in 11.5 g of ethanol solution and stir for 30 min,

[0057] Step 2: Add 104 g of TEOS and 2.25 g of deionized water to the mixed solution, and continue stirring to make it evenly dispersed,

[0058] Step 3: Add 0.1 moL / L hydrochloric acid aqueous solution. After adjusting the pH to 2 for the first time, continue stirring to completely hydrolyze TEOS to form a sol. Add 4 g of graphite and 2 g of conductive carbon that are uniformly mixed and mix them evenly. While stirring, slowly add NH₃·H₂O to adjust the pH to 7. Then pour the sol into the inner lining of the hydrothermal autoclave, place it in an oven at 80 °C and react for 120 min. Adjust the oven to 140 °C to age it and form a wet gel;

[0059] Step 4: Immerse the wet gel in a mixed solution of 10 g of ethanol for 24 h. Then, add 2.1 g of trimethylchlorosilane to 16.5 g of n-hexane to prepare a hydrophobic modifier solution, and immerse the obtained gel in it for hydrophobic modification. After drying under normal pressure and vacuum for 12 h, a carbon-doped silica aerogel is obtained.

[0060] To characterize the performance of the prepared three-dimensional porous silicon-carbon composite aerogel as the positive electrode material for preparing an air electrode, the microstructure of the air electrode sample prepared from the three-dimensional porous silicon-carbon composite aerogel of Example 1 was observed using a scanning electron microscope, and the results are as Figure 1 shown. From Figure 1 and Figure 2 it can be seen that at a magnification of 60.0k, it can be seen that the sample has a loose and porous three-dimensional structure. At a magnification of 35.0k, an obvious loose pore structure can be observed, indicating that the three-dimensional porous silicon-carbon composite aerogel air electrode has been successfully prepared.

[0061] Characterize the performance of the prepared three-dimensional porous silicon-carbon composite aerogel air electrode. The rate performance test of the three-dimensional porous silicon-carbon composite aerogel air electrode sample prepared in Example 1 shows that the voltage change at different current densities is only 0.24 V, indicating excellent stability. When the current density decreases from 5 mA·cm -2 back to 0 mA·cm -2 , its voltage plateau can quickly recover to 1.37 V, which is basically the same as the initial voltage, proving that the material has good rate recovery performance and indicating that the carbon three-dimensional porous silicon-carbon composite aerogel air electrode is successfully prepared.

[0062] The above content is only to illustrate the technical idea of the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution according to the technical idea proposed by the present invention fall within the protection scope of the claims of the present invention.

Claims

1. A preparation method of a three-dimensional porous silicon-carbon composite aerogel, characterized in that: It includes the following steps: Step 1: Dissolve the coupling agent in an organic solvent, mix and stir evenly to obtain mixed solution I; Step 2: Add an organosilane coupling agent and water to mixed solution I, and stir to make it evenly dispersed in the solution to obtain mixed solution II; Step 3: Add an acidic aqueous solution to mixed solution II to adjust the pH value for the first time to make it fully hydrolyzed to form a sol; then add a conductive substance, and then add a basic aqueous solution to adjust the pH value for the second time. Pour the sol into the inner lining of a hydrothermal autoclave and place it in an oven to react for a certain time to obtain a wet gel; Step 4: Immerse the wet gel in an ethanol solution, then take out the wet gel and immerse it in a hydrophobic modifier for modification. After the modification is completed, dry it to obtain a three-dimensional porous silicon-carbon composite aerogel.

2. The preparation method of a three-dimensional porous silicon-carbon composite aerogel according to claim 1, characterized in that: In step 1, the coupling agent is γ-methacryloxypropyltrimethoxysilane, and the addition amount is 1%-5% of the total mass of mixed solution I; the organic solvent is ethanol.

3. The preparation method of a three-dimensional porous silicon carbide composite aerogel according to claim 2, characterized in that: In step 2, the molar ratio of the organosilane coupling agent to water is (3-5):1; the organosilane coupling agent is tetraethyl orthosilicate or tetrabutyl orthosilicate.

4. The preparation method of a three-dimensional porous silicon-carbon composite aerogel according to claim 3, characterized in that: In step 3, the first pH adjustment is 2-3, and the concentration of the acidic aqueous solution is 0.1-0.2 mol / L; the second pH adjustment is 6-7; the concentration of the basic aqueous solution is 0.1-0.2 mol / L.

5. The preparation method of a three-dimensional porous silicon-carbon composite aerogel according to claim 4, characterized in that: In step 3, the reaction temperature in the oven is 40-80 °C, the aging temperature is 120-160 °C, and the reaction time is 100-200 min.

6. Application of a three-dimensional porous silicon-carbon composite aerogel prepared by the preparation method according to claim 1 in the preparation of an air electrode.

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