Methods and applications of constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

Abstract

This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for constructing Si@COF-Co materials using porphyrin COF as a conductive nano-protective layer for nano-silicon and its application. The invention first adds a methanol solution of PEI to a methanol solution of nano-silicon, then dries it at high temperature to obtain PEI-modified nano-silicon Si-PEI. Next, Si-PEI and PVP are dispersed in o-dichlorobenzene / n-butanol, and then COF monomer and glacial acetic acid are added. After maintaining the mixture at 110-130℃ for 70-80 hours, it is washed, dried, and ground to obtain Si@COF. Finally, Si@COF and cobalt acetate tetrahydrate are dispersed in methanol, reacted at room temperature, and then washed, dried, and ground to obtain Si@COF-Co. This invention offers a simple, high-yield, and effective method. The synthesized material effectively alleviates the volume expansion of nano-silicon, improves the stability and reversibility of the electrode material, and can be used as a negative electrode material for lithium-ion batteries.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for constructing Si@COF-Co materials using porphyrin COF as a conductive nano-protective layer for silicon nanomaterials and its application. Background Technology

[0002] In the field of energy storage, silicon nanoparticles possess extremely high theoretical capacity, but their severe volume expansion greatly limits their application. Currently, commercially available silicon-based anode materials composed of silicon and graphite, as well as silicon-carbon composite materials, are mainly used. However, silicon mixing can only slightly improve the specific capacity of the electrode material and cannot fundamentally solve the problem of volume expansion. Furthermore, the problem of repeated formation of the solid electrolyte interphase (SEI) film during the expansion process due to direct contact between silicon and the electrolyte remains unresolved. Therefore, it is necessary to start from the silicon interface layer to fundamentally solve the problem of SEI film rupture and formation caused by silicon volume expansion, thereby effectively improving the stability and cycle life of electrode materials.

[0003] Given the aforementioned problems, developing a coating material that can alleviate the volume expansion of silicon is of great significance. Covalent organic framework materials, with their large specific surface area and numerous pore sizes, are excellent coatings for nano-silicon. Therefore, combining nano-silicon with covalent organic framework materials and designing them into a conductive nano-protective layer is an ideal solution. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, this invention constructs Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for silicon nanoparticles. This material is used as a negative electrode material for lithium-ion batteries, which can effectively alleviate the volume expansion of silicon nanoparticles, improve the stability and reversibility of electrode materials, and enhance the interaction force between active materials and current collectors. It has great development prospects in the field of energy storage.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] The first aspect of this invention provides a method for constructing Si@COF-Co materials using porphyrin COF as a conductive nano-protective layer for silicon nanoparticles, comprising the following steps:

[0007] S1. A brown solid was obtained by mixing a nano-silicon methanol solution with a polyethyleneimine (PEI) methanol solution, stirring at room temperature, and then washing with ethanol. The solid was then dried and ground into powder to obtain powdered PEI-modified nano-silicon Si-PEI.

[0008] S2. Disperse Si-PEI and polyvinylpyrrolidone (PVP) in a mixture of o-dichlorobenzene / n-butanol, then add monomers 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and 2,5-dihydroxyterephthalaldehyde (DHA), dissolve them, then add glacial acetic acid and stir at room temperature;

[0009] S3. Add glacial acetic acid to the mixed solution obtained in step S2, degas and remove oxygen, and react at 110-130℃ for 70-80h. After the reaction, wash, dry and grind into powder to obtain Si@COF.

[0010] S4. Si@COF and cobalt acetate tetrahydrate were dispersed in methanol, stirred at room temperature, and the product was collected. After washing, drying, and grinding into powder, Si@COF-Co was obtained.

[0011] This invention utilizes nano-silicon, polyethyleneimine, polyvinylpyrrolidone, 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin, cobalt acetate tetrahydrate, and 2,5-dihydroxyterephthalaldehyde (DHA) as raw materials, and successfully prepares Si@COF-Co with a large amount of porphyrin COF as a conductive nano-protective layer for silicon through hydrothermal reaction. Because the Si@COF-Co prepared by this invention has a porous porphyrin COF coating, the volume expansion of silicon is significantly reduced. Furthermore, the COF-Co coating contains a large amount of Co. 2+ The cross-linking network formed by the binder sodium alginate enhances the interaction between the active material and the current collector, thereby mitigating the expansion and shedding of the electrode material during charging and discharging. Simultaneously, the silicon conductive nano-protective layer Si@COF-Co prepared in this invention effectively prevents direct contact between silicon and the electrolyte, thus generating a stable solid electrolyte interphase (SEI) film, effectively promoting lithium-ion transport and significantly reducing capacity loss. Therefore, the Si@COF-Co structure constructed using porphyrin COF as the silicon conductive nano-protective layer in this invention effectively alleviates the volume expansion of nano-silicon, improves the stability and reversibility of the electrode material, and enhances the interaction between the active material and the current collector, showing great promise in the energy storage field.

[0012] Preferably, in S1, the concentration of the nano-silicon methanol solution is 10-20 mg / mL, and the concentration of the PEI methanol solution is 50-100 mg / mL.

[0013] Preferably, in S1, the stirring time at room temperature is 1-4 hours, and the stirring speed is 500-1000 r / min.

[0014] Preferably, in S2, the mass ratio of Si-PEI, polyvinylpyrrolidone, 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin (TPH), and 2,5-dihydroxyterephthalaldehyde is 590-610:490-510:40-43:73-77; and the concentration of Si-PEI in the o-dichlorobenzene / n-butanol mixture is 6 mg / 1-2 mL.

[0015] Preferably, in the o-dichlorobenzene / n-butanol mixture of S2, the volume ratio of o-dichlorobenzene to n-butanol is 1:1.

[0016] Preferably, in S2, the stirring time at room temperature is 3-6 hours and the stirring speed is 300-600 r / min.

[0017] Preferably, the concentration of glacial acetic acid in S2 and S3 is 5-7M, wherein the amount of S2 used is 350-450uL per 120mg Si-PEI; and the amount of S3 used is 550-650uL per 120mg Si-PEI.

[0018] Preferably, in S4, the mass ratio of Si@COF to cobalt acetate tetrahydrate is 1-2:1-2, and the concentration of Si@COF in methanol is 5 mg / 1-2 mL.

[0019] Preferably, in step S4, the stirring time at room temperature is 10-15 hours, and the stirring speed is 500-800 r / min.

[0020] The second aspect of the present invention provides a Si@COF-Co material prepared by the method described in the first aspect, with porphyrin COF as a conductive nano-protective layer for silicon nanoparticles.

[0021] The third aspect of this invention provides the application of the Si@COF-Co material described in the second aspect, which uses porphyrin COF as a nano-silicon conductive nano-protective layer, in the field of energy storage.

[0022] Preferably, the Si@COF-Co material is used as a negative electrode material for lithium-ion batteries. The Si@COF-Co material obtained according to the method of the present invention, constructed with porphyrin COF as a silicon conductive nanolayer, can be used as a negative electrode material for lithium-ion batteries in the energy storage field.

[0023] Compared with the prior art, the beneficial effects of the present invention are:

[0024] This invention uses nano-silicon, polyethyleneimine, polyvinylpyrrolidone, 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin, cobalt acetate tetrahydrate, and 2,5-dihydroxyterephthalaldehyde (DHA) as raw materials. First, a methanol solution of PEI is added to a methanol solution of nano-silicon to obtain a brown solid, which is then dried at high temperature to obtain PEI-modified nano-silicon (Si-PEI). Then, the obtained Si-PEI and PVP are dispersed in o-dichlorobenzene / n-butanol, and COF monomers (TPH and DHA) are added. After complete dispersion and dissolution, glacial acetic acid is added, and the mixture is kept at 110-130℃ for 70-80 hours. After washing, drying, and grinding, Si@COF is obtained. Finally, Si@COF and cobalt acetate tetrahydrate are dispersed in methanol, reacted at room temperature, washed, dried, and ground to obtain a brown powder, thus obtaining Si@COF-Co. The Si@COF-Co material prepared in this invention, using porphyrin COF as a silicon conductive nanolayer protective layer, not only improves the conductivity of silicon-based anodes but also effectively mitigates the significant volume expansion of silicon during the charging and discharging process of lithium-ion batteries, thereby improving the cycle life and stability of the electrode material. Therefore, the synthesis method of this invention is simple and effective, and the synthesized product can effectively alleviate the volume expansion of nano-silicon, improve the stability and reversibility of the electrode material, and can be used as a lithium-ion battery anode material. Specifically, this invention has the following advantages:

[0025] (1) The preparation method is simple, efficient and has a high yield; the composite material Si@COF-Co is uniformly synthesized by hydrothermal reaction of nano-silicon, polyethyleneimine, polyvinylpyrrolidone, 5,10,15,20-tetra(4-aminobenzene)-21H,23H-porphyrin, cobalt acetate tetrahydrate and 2,5-dihydroxyterephthalaldehyde (DHA). The yield of porphyrin COF is as high as 90% or more, and more than 500 mg of target material can be obtained by one feeding.

[0026] (2) Good preparation effect; SEM and TEM showed that the synthesized composite material had a uniform morphology, and the formed conductive protective layer was only a few nanometers in size. High-resolution transmission electron microscopy showed that the silicon lattice fringes were relatively clear, and the measured lattice spacing was about 0.31 nm, corresponding to the (111) crystal plane of silicon. Thermogravimetric analysis showed that the composite material had a uniform morphology, and the formed conductive protective layer was only a few nanometers in size. Figure 3 It can be observed that silicon accounts for 89.49% of the prepared silicon nanolayer protective material.

[0027] (3) Alleviating the volume expansion of silicon and improving electrode stability and reversibility; from Figure 7 It can be concluded that the prepared material still has a stable specific capacity at high current density, while the comparative material is pure silicon ( Figure 8 The performance is very poor, indicating that the porphyrin COF protective layer structure can alleviate the volume expansion of silicon and improve the stability and reversibility of the electrode. Attached Figure Description

[0028] Figure 1 The image shows a scanning electron microscope image of the Si@COF-Co prepared in Example 1.

[0029] Figure 2 This is a high-resolution transmission electron microscope image of Si@COF-Co prepared in Example 2.

[0030] Figure 3 The thermogravimetric curves of Si@COF prepared in Example 5 are shown.

[0031] Figure 4 The image shows the Raman spectrum of the Si@COF-Co electrode prepared in Example 4.

[0032] Figure 5 The impedance spectrum of Si@COF-Co in Example 3 is shown.

[0033] Figure 6 The cyclic voltammetry curves for Si@COF-Co in Example 3 are shown.

[0034] Figure 7 The cycling performance curve (1000 mA·g) of Si@COF-Co in Example 6 is shown. -1 (Under current density).

[0035] Figure 8 The cycling performance curve (1000 mA·g) of the comparative sample pure silicon in Example 6 is shown. -1 (Under current density). Detailed Implementation

[0036] The specific embodiments of the present invention will be further described below. It should be noted that these descriptions are for the purpose of aiding understanding the present invention, but do not constitute a limitation thereof. Furthermore, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods, and the experimental materials used in the following embodiments are all available through conventional commercial channels.

[0038] Example 1: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0039] (1) Weigh 200mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 20mg / mL.

[0040] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 1 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 100 mg / mL.

[0041] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol. Place the brown solid obtained at 60 °C for 12 h to dry. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0042] (4) Weigh 120 mg of Si-PEI and 100 mg of polyvinylpyrrolidone (PVP) and add them to 20 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate for 15 min to ensure complete dissolution of the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and sonicate for 15 min to ensure complete dispersion of the solid. Then add 200 μL of glacial acetic acid (6M) and stir at room temperature for 4 h. The resulting reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three deoxygenation treatments of liquid nitrogen freezing / thawing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0043] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate into 10 mL of methanol, and sonicate for 15 min to completely dissolve the solid. Then stir at 600 r / min for 12 h at room temperature, centrifuge to collect the product, wash it several times with methanol, vacuum dry it at 60 °C for 12 h, and grind it into powder to obtain Si@COF-Co.

[0044] (6) Figure 1 As shown, the morphology analysis of the material using scanning electron microscopy revealed that the prepared Si@COF-Co has a uniform spherical morphology with a size of approximately 100 nm and good dispersibility, with virtually no agglomeration.

[0045] Example 2: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0046] (1) Weigh 100mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 10mg / mL.

[0047] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 2 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 50 mg / mL.

[0048] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol by centrifugation. Place the brown solid obtained at 60℃ and dry it at high temperature for 12 h. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0049] (4) Weigh 120 mg of Si-PEI and 100 mg of polyvinylpyrrolidone (PVP) and add them to 20 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate for 15 min to ensure complete dissolution of the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and sonicate for 15 min to ensure complete dispersion of the solid. Then add 200 μL of glacial acetic acid (6M) and stir at room temperature for 4 h. The resulting reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three treatments of liquid nitrogen freezing / thawing degassing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0050] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate into 10 mL of methanol, and disperse by ultrasonication for 15 min to ensure complete dissolution of the solid. Then stir at 600 r / min for 12 h at room temperature, collect the product by centrifugation, wash several times with methanol, dry under vacuum at 60 °C for 12 h, and grind into powder (brown powder) to obtain Si@COF-Co.

[0051] (6) Figure 2As shown, the structure of the material was analyzed by transmission electron microscopy. It was found that the prepared Si@COF-Co had obvious lattice stripes. The lattice spacing was measured to be 0.31 nm, corresponding to the (111) crystal plane of silicon. A COF-Co protective layer with a thickness of 2.98 nm was also found in the figure, which proved the successful synthesis of Si@COF-Co material.

[0052] Example 3: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0053] (1) Weigh 200mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 20mg / mL.

[0054] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 1 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 100 mg / mL.

[0055] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol. Place the brown solid obtained at 60 °C for 12 h to dry. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0056] (4) Weigh 120 mg of Si-PEI and 100 mg of polyvinylpyrrolidone (PVP) and add them to 10 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate for 15 min to ensure complete dissolution of the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and sonicate for 15 min to ensure complete dispersion of the solid. Subsequently, add 200 μL of glacial acetic acid (6 M) and stir at room temperature for 4 h. The resulting reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three deoxygenation treatments of liquid nitrogen freezing / thawing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0057] (5) Weigh 100 mg of Si@COF and 100 mg of cobalt acetate tetrahydrate into 10 mL of methanol, and disperse by ultrasonication for 15 min to completely dissolve the solid. Then stir at 600 r / min for 12 h at room temperature, collect the product by centrifugation, wash several times with methanol, dry under vacuum at 60 °C for 12 h, and grind into powder (brown powder) to obtain Si@COF-Co.

[0058] (6) Si@COF-Co material was mixed with conductive agent (CNTs) and binder (sodium alginate) at a mass ratio of 7:2:1. Solvent water was added and stirred at room temperature for 12 hours to obtain a slurry. This slurry was then coated onto a 12µm thick copper foil, dried at 60℃ for 12 hours, and cut into 14nm circular electrode sheets for later use. One circular electrode sheet was weighed to a certain mass (0.5mg-1mg), and assembled with a PP separator and a 15.6mm lithium sheet in an argon atmosphere glove box. The assembly was then sealed using a sealing machine at a pressure of 100MPa and allowed to stand for 24 hours to obtain a button cell with Si@COF-Co as the negative electrode and lithium sheet as the positive electrode. Cyclic voltammetry testing of the battery was performed using an electrochemical workstation (CHI 750D). Figure 6 AC impedance testing Figure 5 The study found that the material has high reversibility and low impedance, indicating that conductive porphyrin COF (COF-Co) can effectively improve the conductivity of silicon and accelerate the lithium-ion transport rate.

[0059] Example 4: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0060] (1) Weigh 200mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 20mg / mL.

[0061] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 1 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 100 mg / mL.

[0062] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol. Place the brown solid obtained at 60 °C for 12 h to dry. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0063] (4) Weigh 240 mg of Si-PEI and 200 mg of polyvinylpyrrolidone (PVP) and add them to 20 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate for 15 min to ensure complete dissolution of the solid. Then add 30 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 16.4 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH), and sonicate for 15 min to ensure complete dispersion of the solid. Then add 200 μL of glacial acetic acid (6 M) and stir at room temperature for 4 h. The resulting reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three deoxygenation treatments of liquid nitrogen freezing / thawing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0064] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate into 10 mL of methanol, and disperse by ultrasonication for 15 min to ensure complete dissolution of the solid. Then stir at 600 r / min for 12 h at room temperature, collect the product by centrifugation, wash several times with methanol, dry under vacuum at 60 °C for 12 h, and grind into powder (brown powder) to obtain Si@COF-Co.

[0065] (6) Following the method in Example 3, Si@COF-Co was prepared into an electrode, and Raman spectroscopy was performed on the electrode to obtain its composition structure, such as... Figure 4 As shown, a strong characteristic peak of nano-silicon appears at 520nm, while the D-band and G-band characteristic peaks of carbon appear at around 1350nm and 1590nm, which belong to conductive agents CNTs, which is consistent with the electrode fabrication process.

[0066] Example 5: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0067] (1) Weigh 200mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 20mg / mL.

[0068] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 1 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 100 mg / mL.

[0069] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol. Place the brown solid obtained at 60 °C for 12 h to dry. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0070] (4) Weigh 120 mg of Si-PEI and 100 mg of polyvinylpyrrolidone (PVP) and add them to 20 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate the mixture for 15 min to ensure complete dissolution of the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and sonicate for 15 min to ensure complete dispersion of the solid. Finally, add 200 μL of glacial acetic acid (6 M) and stir at room temperature for 4 h. The resulting reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three deoxygenation treatments of liquid nitrogen freezing / thawing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0071] (5) Weigh 100 mg of Si@COF and 100 mg of cobalt acetate tetrahydrate into 10 mL of methanol, and disperse by ultrasonication for 15 min to completely dissolve the solid. Then stir at 600 r / min for 12 h at room temperature, collect the product by centrifugation, wash several times with methanol, dry under vacuum at 60 °C for 12 h, and grind into powder (brown powder) to obtain Si@COF-Co.

[0072] (6) Thermogravimetric analysis was performed on the Si@COF material to determine the silicon content in the material, such as... Figure 3 As shown, the material was heated in air at a rate of 10℃ / min, with a temperature range of 30-900℃. The figure reveals that thermal decomposition occurs in the 350-650℃ range, primarily due to the decomposition of the protective porphyrin COF layer. Above 650℃, the mass increases because the oxidation temperature of silicon is reached, leading to partial silicon oxidation to form silicon dioxide. Analysis shows that the silicon content in the material is 89.49%.

[0073] Example 6: Constructing Si@COF-Co materials using porphyrin COF as a conductive nanolayer for silicon nanomaterials

[0074] (1) Weigh 200mg of nano-silicon (50-100 nanometers) and add it to 10mL of methanol. Sonicate for more than 30min until the silicon is completely dispersed in the methanol to prepare a nano-silicon methanol solution. The concentration of nano-silicon in the methanol solution is 20mg / mL.

[0075] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 1 mL of methanol. Disperse it by sonication for 30 min to prepare a PEI methanol solution. The concentration of polyethyleneimine in the methanol solution is 100 mg / mL.

[0076] (3) Take 1 mL of PEI methanol solution and slowly add it dropwise to the methanol solution of silicon. Then stir the mixture at room temperature for 2 h at a stirring speed of 600 r / min. Then wash it 4 times with anhydrous ethanol. Place the brown solid obtained at 60 °C for 12 h to dry. Grind the product into powder and store it in a desiccator to obtain powdered PEI modified nano silicon (Si-PEI).

[0077] (4) Weigh 120 mg of Si-PEI and 100 mg of polyvinylpyrrolidone (PVP) and add them to 10 mL of o-dichlorobenzene / n-butanol (v / v = 1:1) mixture. Sonicate for 15 min to ensure complete dissolution of the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetratetra(4-aminophenyl)-21H,23H-porphyrin (TPH) and sonicate for 15 min to ensure complete dispersion of the solid. Subsequently, add 200 μL of glacial acetic acid (6 M) and stir at room temperature for 4 h. The reaction solution was then transferred to a 50 mL vacuum reaction tube, and 600 μL of glacial acetic acid (6 M) was added. After three deoxygenation treatments of liquid nitrogen freezing / thawing, the mixture was heated at 120 °C for 72 h. After the reaction, the mixture was cooled to room temperature, centrifuged to collect the product, washed several times with tetrahydrofuran, dried under vacuum at 60 °C for 12 h, and ground into powder (brown powder) to obtain Si@COF.

[0078] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate into 5 mL of methanol, and sonicate for 15 min to completely dissolve the solid. Then stir at 600 r / min for 12 h at room temperature, centrifuge to collect the product, wash it several times with methanol, vacuum dry it at 60 °C for 12 h, and grind it into powder (brown powder) to obtain Si@COF-Co.

[0079] (6) According to Example 3, Si@COF-Co and pure nano-silicon button batteries were prepared respectively, and their cycle performance was tested using a Blue Battery Testing System. Figure 7 As shown, Si@COF-Co material can withstand high current densities of 1000 mA·g. -1 It can maintain 2099.4 mAh·g after 500 cycles.-1 The discharge specific capacity, compared with pure silicon (such as...) Figure 8 It was found that the performance of pure nano-silicon decays rapidly, indicating that Si@COF-Co material has excellent cycle performance, and the porphyrin COF protective layer can effectively suppress the volume expansion of nano-silicon, thereby maintaining the stability of battery material performance.

[0080] Overall, scanning electron microscopy (SEM) Figure 1 The high-resolution transmission electron microscope (HRTEM) shows that the material has a uniform spherical morphology. Figure 2 The results show that a stable porphyrin COF layer exists in Si@COF-Co, and the composite material has obvious lattice fringes, which correspond to the (111) crystal plane of silicon. TGA curves ( Figure 3 The data shows that silicon constitutes a large proportion of the silicon protective layer material. Raman spectra ( Figure 4 This indicates the presence of strong silicon characteristic peaks. (EIS spectrum) Figure 5 ), Cyclic voltammetry curve ( Figure 6 ), Cyclic performance curves ( Figure 7 ) and compared with the cycling performance of pure silicon ( Figure 8 The results show that Si@COF-Co significantly improves the conductivity and cycling performance of silicon at high current densities.

[0081] The embodiments of the present invention have been described in detail above, but the present invention is not limited to the described embodiments. For those skilled in the art, various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and these variations still fall within the protection scope of the present invention.

Claims

1. A method for constructing Si@COF-Co materials using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials, characterized in that, The Si@COF-Co material is mixed with a conductive agent and sodium alginate binder to prepare a negative electrode slurry; the preparation method of the Si@COF-Co material includes the following steps: S1. A brown solid was obtained by mixing a nano-silicon methanol solution with a polyethyleneimine (PEI) methanol solution, stirring at room temperature, and then washing with ethanol. The solid was then dried and ground into powder to obtain powdered PEI-modified nano-silicon Si-PEI. S2. Si-PEI and polyvinylpyrrolidone are dispersed in a mixture of o-dichlorobenzene / n-butanol, and then monomers 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde are added. After dissolution, glacial acetic acid is added and the mixture is stirred at room temperature. The mass ratio of Si-PEI, polyvinylpyrrolidone, 5,10,15,20-tetra(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde is 590-610:490-510:40-43:73-77. S3. Add glacial acetic acid to the mixed solution obtained in step S2, degas and remove oxygen, and react at 110-130℃ for 70-80 h. After the reaction, wash, dry and grind into powder to obtain Si@COF. S4. Si@COF and cobalt acetate tetrahydrate were dispersed in methanol, stirred at room temperature, and the product was collected. After washing, drying, and grinding into powder, Si@COF-Co was obtained.

2. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, In S1, the concentration of the nano-silicon methanol solution is 10-20 mg / mL, and the concentration of the PEI methanol solution is 50-100 mg / mL.

3. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, In S1, the stirring time at room temperature is 1-4 h, and the stirring speed is 500-1000 r / min; in S2, the stirring time at room temperature is 3-6 h, and the stirring speed is 300-600 r / min; in S4, the stirring time at room temperature is 10-15 h, and the stirring speed is 500-800 r / min.

4. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, In S2, the concentration of Si-PEI in the o-dichlorobenzene / n-butanol mixture is 6 mg / 1-2 mL.

5. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, In the S2 mixture of o-dichlorobenzene and n-butanol, the volume ratio of o-dichlorobenzene to n-butanol is 1:

1.

6. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, The concentration of glacial acetic acid in S2 and S3 is 5-7M, with S2 being used at 350-450 uL per 120 mg Si-PEI and S3 being used at 550-650 uL per 120 mg Si-PEI.

7. The method for constructing Si@COF-Co material using porphyrin COF as a conductive nano-protective layer for lithium-ion battery anode materials according to claim 1, characterized in that, In S4, the mass ratio of Si@COF to cobalt acetate tetrahydrate is 1-2:1-2, and the concentration of Si@COF in methanol is 5 mg / 1-2 mL.

8. The Si@COF-Co material for use as a conductive nano-silicon nanolayer, prepared by the method according to any one of claims 1-7, and applied to the negative electrode material of lithium-ion batteries.

9. The application of the Si@COF-Co material with porphyrin COF as a nano-silicon conductive nano-protective layer, as described in claim 8, in the field of energy storage.

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