Method for constructing Si (at) COF-Co material by taking porphyrin COF as nanometer silicon conductive nanometer protective layer and application of Si (at) COF-Co material

Abstract

The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for constructing a Si (at) COF-Co material by taking porphyrin COF as a nanometer silicon conductive nanometer protective layer and application of the Si (at) COF-Co material. The preparation method comprises the following steps: firstly, adding a methanol solution of PEI into a methanol solution of nano silicon, and then drying at high temperature to prepare PEI modified nano silicon Si-PEI; then dispersing Si-PEI and PVP in o-dichlorobenzene / n-butyl alcohol, then adding a COF monomer and glacial acetic acid, keeping at 110-130 DEG C for 70-80 hours, and then washing, drying and grinding to obtain Si (COF); and finally, dispersing the Si-coated COF and cobalt acetate tetrahydrate in methanol, reacting at room temperature, washing, drying and grinding to obtain the Si-coated COF-Co. The method is simple and convenient, the yield is high, the effect is good, the compound can effectively relieve volume expansion of nano silicon, the stability and reversibility of an electrode material are improved, and the compound can be used as a lithium ion battery negative electrode material.

Description

Technical Field

[0001] The invention belongs to the technical field of lithium ion batteries, and specifically relates to a method for constructing a Si@COF-Co material using porphyrin COF as a nano-silicon conductive nano-protective layer and an application thereof. Background Art

[0002] In the field of energy storage, silicon nanoparticles have an ultra-high theoretical capacity, but their severe volume expansion greatly limits their application. Currently, silicon-based negative electrode materials and silicon-carbon composite materials made of a mixture of silicon and graphite are mainly used commercially, but the mixing of silicon can only slightly increase the specific capacity of the electrode material, and cannot fundamentally solve the problem of volume expansion. In addition, the problem of repeated generation of the solid electrolyte interface film (SEI film) caused by the expansion process caused by direct contact between silicon and the electrolyte has not been solved. Therefore, it is necessary to start from the silicon interface layer and fundamentally solve the problem of the rupture and generation of the SEI film caused by the volume expansion of silicon, thereby effectively improving the stability and cycle life of the electrode material.

[0003] Based on the above problems, it is of great significance to develop a coating material that can alleviate the volume expansion of silicon. Among them, covalent organic framework materials have a large specific surface area and more pores, and are excellent coatings for nano-silicon. Therefore, it is an ideal solution to combine nano-silicon with covalent organic framework materials and design them into a conductive nano protective layer. Summary of the invention

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

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

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

[0007] S1, mixing the nano-silicon methanol solution with the polyethyleneimine PEI methanol solution, stirring at room temperature and then washing with ethanol to obtain a brown solid, and then drying and grinding into powder to obtain powdery PEI-modified nano-silicon Si-PEI;

[0008] S2, dispersing Si-PEI and polyvinylpyrrolidone (PVP) in a mixture of o-dichlorobenzene / n-butanol, adding monomers 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH) and 2,5-dihydroxyterephthalaldehyde (DHA), adding glacial acetic acid after dissolution and stirring at room temperature;

[0009] S3, adding glacial acetic acid to the mixed solution obtained in step S2, reacting at 110-130° C. for 70-80 hours after degassing and deoxygenation, washing, drying, and grinding into powder after the reaction to obtain Si@COF;

[0010] S4. Disperse Si@COF and cobalt acetate tetrahydrate in methanol, stir at room temperature, collect the product, wash, dry, and grind into powder to obtain Si@COF-Co.

[0011] The present invention uses nano-silicon, polyethyleneimine, polyvinylpyrrolidone, 5,10,15,20-tetrakis (4-aminophenyl)-21H,23H-porphyrin, cobalt acetate tetrahydrate and 2,5-dihydroxyterephthalaldehyde (DHA) as raw materials, and after hydrothermal reaction, successfully prepares Si@COF-Co with a large amount of porphyrin COF as a silicon conductive nano protective layer. Since the Si@COF-Co prepared by the present invention has a porous porphyrin COF as a coating, the volume expansion of silicon can be greatly slowed down. In addition, there is a large amount of Co in the COF-Co coating. 2+ And it can cross-link with the binder sodium alginate to form a stable cross-linked network, and then it can enhance the interaction between the active material and the current collector, thereby alleviating the expansion and shedding of the electrode material during the charge and discharge process. At the same time, the silicon conductive nano protective layer Si@COF-Co prepared by the present invention can effectively avoid direct contact between silicon and the electrolyte, and then can produce a stable solid electrolyte interface film (SEI film), effectively promote the transmission of lithium ions, and greatly reduce the loss of capacity. Therefore, the Si@COF-Co constructed with porphyrin COF as the silicon conductive nano protective layer of the present invention can effectively alleviate the volume expansion of nano silicon, improve the stability and reversibility of the electrode material, enhance the interaction between the active material and the current collector, and has a great development prospect in the field of energy storage.

[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 h, and the rotation speed is 500-1000 r / min.

[0014] Preferably, in S2, the mass ratio of Si-PEI, polyvinylpyrrolidone, 5,10,15,20-tetrakis(4-aminophenyl)-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 mixed solution 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 h, and the rotation 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 is 350-450uL per 120mg Si-PEI; the amount of S3 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 S4, the stirring time at room temperature is 10-15 h, and the rotation 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 and using porphyrin COF as a nano-silicon conductive nano-protective layer.

[0021] The third aspect of the present invention provides the application of the Si@COF-Co material described in the second aspect using porphyrin COF as the 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 obtained by the method of the present invention, which is constructed with porphyrin COF as a silicon conductive nano protective layer, is used in the field of energy storage and can be used as a negative electrode material for lithium-ion batteries.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The invention uses nano silicon, polyethyleneimine, polyvinyl pyrrolidone, 5,10,15,20-tetrakis (4-aminophenyl)-21H,23H-porphyrin, tetrahydrated cobalt acetate and 2,5-dihydroxyterephthalaldehyde (DHA) as raw materials, firstly adds a methanol solution of PEI into a nano silicon methanol solution to obtain a brown solid, and then performs high temperature drying to obtain PEI modified nano silicon (Si-PEI); then the obtained Si-PEI and PVP are dispersed in o-dichlorobenzene / n-butanol, COF monomers (TPH and DHA) are added, and glacial acetic acid is added after the monomers are completely dispersed and dissolved, and the mixture is kept at 110-130 DEG C for 70-80 hours, and then washed, dried and ground to obtain Si@COF; finally, Si@COF and tetrahydrated cobalt acetate are dispersed in methanol, reacted at room temperature, and then washed, dried and ground to obtain brown powder to obtain Si@COF-Co. The Si@COF-Co material prepared by the present invention with porphyrin COF as the silicon conductive nano protective layer can not only improve the conductivity of the silicon-based negative electrode, but also effectively slow down the huge 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 the present invention is simple and effective, and the synthetic product can effectively slow down the volume expansion of nano silicon, improve the stability and reversibility of the electrode material, and can be used as a negative electrode material for lithium-ion batteries. Specifically, the present invention has the following advantages:

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

[0026] (2) Good preparation effect: SEM and TEM show that the synthesized composite material has a uniform morphology, and the conductive protective layer formed is only a few nanometers. High-resolution transmission electron microscopy shows that the lattice stripes of silicon are relatively clear. The lattice spacing is measured to be about 0.31nm, corresponding to the (111) crystal plane of silicon. Figure 3 It can be found that the proportion of silicon in the prepared silicon nano protective layer material is 89.49%.

[0027] (3) Alleviate the volume expansion of silicon and improve electrode stability and reversibility; Figure 7 It can be concluded that the prepared material still has a stable specific capacity at high current density, while the comparison material pure silicon ( Figure 8 ) has very poor performance, indicating that the porphyrin COF protective layer structure can alleviate the volume expansion of silicon and improve the electrode stability and reversibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a scanning electron microscope image of 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 This is the thermogravimetric curve of Si@COF prepared in Example 5.

[0031] Figure 4 This is the Raman spectrum of the Si@COF-Co electrode prepared in Example 4.

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

[0033] Figure 6 This is the cyclic voltammetry curve of Si@COF-Co in Example 3.

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

[0035] Figure 8 The cycle performance curve of pure silicon of the comparative sample in Example 6 (1000 mA·g -1 current density). DETAILED DESCRIPTION

[0036] The specific embodiments of the present invention are further described below. It should be noted that the description of these embodiments is used to help understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in each embodiment of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The experimental methods in the following examples are conventional methods unless otherwise specified, and the experimental materials used in the following examples are commercially available unless otherwise specified.

[0038] Example 1: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0039] (1) Weigh 200 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 20 mg / mL.

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

[0041] (3) 1 mL of PEI methanol solution was slowly added dropwise to the methanol solution of silicon, and the mixed solution was stirred at room temperature for 2 h at a stirring speed of 600 r / min. The mixed solution was then centrifuged and washed four times with anhydrous ethanol. The obtained brown solid was dried at 60°C for 12 h. The obtained product was ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and disperse them by ultrasonication for 15 min to completely dissolve the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and disperse them by ultrasonication for 15 min to completely disperse 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. The solution was degassed by freezing / thawing with liquid nitrogen three times for deoxygenation and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature, and the product was collected by centrifugation and washed several times with tetrahydrofuran, dried in a 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 in 10 mL of methanol, and ultrasonically disperse 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 it several times with methanol, dry it in a vacuum at 60 ° C for 12 h, and grind it into powder to obtain Si@COF-Co.

[0044] (6) Figure 1 As shown, the morphology of the material was analyzed by scanning electron microscopy, and it was found that the prepared Si@COF-Co had a uniform spherical morphology with a size of about 100 nm and had good dispersibility, and the material was basically not agglomerated.

[0045] Example 2: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0046] (1) Weigh 100 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 10 mg / mL.

[0047] (2) Weigh 100 mg of polyethyleneimine (PEI) and add it to 2 mL of methanol. Ultrasonic dispersion is performed 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 mixed solution at room temperature for 2 h at a stirring speed of 600 r / min. Then, use anhydrous ethanol for centrifugal washing 4 times. The obtained brown solid is placed at 60°C for high temperature drying for 12 h. The obtained product is ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and disperse them by ultrasonication for 15 min to completely dissolve the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and disperse them by ultrasonication for 15 min to completely disperse 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. The solution was degassed by freezing / thawing with liquid nitrogen three times and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature and the product was collected by centrifugation. The product was washed several times with tetrahydrofuran and dried at 60 ° C for 12 h. The product was ground into powder (brown powder) to obtain Si@COF.

[0050] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate in 10 mL of methanol and disperse them ultrasonically 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 it with methanol several times, dry it in vacuum at 60 ° C for 12 h, and grind it into powder (brown powder) to obtain Si@COF-Co.

[0051] (6) Figure 2As shown, the material was structurally analyzed using a transmission electron microscope, and it was found that the prepared Si@COF-Co had obvious lattice fringes. The lattice spacing was measured to be 0.31nm, corresponding to the (111) crystal plane of silicon, and a COF-Co protective layer with a thickness of 2.98nm was found in the figure, proving the successful synthesis of the Si@COF-Co material.

[0052] Example 3: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0053] (1) Weigh 200 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 20 mg / mL.

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

[0055] (3) 1 mL of PEI methanol solution was slowly added dropwise to the methanol solution of silicon, and the mixed solution was stirred at room temperature for 2 h at a stirring speed of 600 r / min. The mixed solution was then centrifuged and washed four times with anhydrous ethanol. The obtained brown solid was dried at 60°C for 12 h. The obtained product was ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and disperse them by ultrasonication for 15 min to completely dissolve the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and disperse them by ultrasonication for 15 min to completely disperse 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. The solution was degassed by freezing / thawing with liquid nitrogen three times for deoxygenation and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature, and the product was collected by centrifugation and washed several times with tetrahydrofuran, dried in a 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 in 10 mL of methanol and disperse them ultrasonically 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 it with methanol several times, dry it in vacuum at 60 ° C for 12 h, and grind it into powder (brown powder) to obtain Si@COF-Co.

[0058] (6) Si@COF-Co material was mixed with conductive agent (CNTs) and adhesive (sodium alginate) in a mass ratio of 7:2:1, and solvent water was added and stirred at room temperature for 12 hours to obtain a slurry, which was then coated on a 12um thick copper foil, dried at 60°C for 12 hours, and cut into 14nm circular electrodes for standby use. Take a circular electrode, weigh a certain mass (0.5mg-1mg), assemble it with a PP diaphragm and a 15.6mm lithium sheet in an argon atmosphere glove box, and seal it with a sealing machine at a pressure of 100Mpa. After standing for 24 hours, a button battery with Si@COF-Co as the negative electrode and a lithium sheet as the positive electrode was obtained. The battery was subjected to cyclic voltammetry test (CVI) using an electrochemical workstation (CHI 750D). Figure 6 )、AC impedance test( Figure 5 ), and found that the material has high reversibility and low impedance value, indicating that conductive porphyrin COF (COF-Co) can effectively improve the conductivity of silicon and accelerate the transmission rate of lithium ions.

[0059] Example 4: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0060] (1) Weigh 200 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 20 mg / mL.

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

[0062] (3) 1 mL of PEI methanol solution was slowly added dropwise to the methanol solution of silicon, and the mixed solution was stirred at room temperature for 2 h at a stirring speed of 600 r / min. The mixed solution was then centrifuged and washed four times with anhydrous ethanol. The obtained brown solid was dried at 60°C for 12 h. The obtained product was ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and disperse them by ultrasonication for 15 min to completely dissolve the solid. Then add 30 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 16.4 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and disperse them by ultrasonication for 15 min to completely disperse 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, 600 μL of glacial acetic acid (6 M) was added, and the solution was degassed by freezing / thawing with liquid nitrogen three times for deoxygenation and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature and then centrifuged to collect the product, washed several times with tetrahydrofuran, and vacuum dried at 60 ° C for 12 h. Si@COF was obtained after grinding into powder (brown powder).

[0064] (5) Weigh 50 mg of Si@COF and 50 mg of cobalt acetate tetrahydrate in 10 mL of methanol and disperse them ultrasonically 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 it with methanol several times, dry it in vacuum at 60 ° C for 12 h, and grind it into powder (brown powder) to obtain Si@COF-Co.

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

[0066] Example 5: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0067] (1) Weigh 200 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 20 mg / mL.

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

[0069] (3) 1 mL of PEI methanol solution was slowly added dropwise to the methanol solution of silicon, and the mixed solution was stirred at room temperature for 2 h at a stirring speed of 600 r / min. The mixed solution was then centrifuged and washed four times with anhydrous ethanol. The obtained brown solid was dried at 60°C for 12 h. The obtained product was ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and then ultrasonically disperse for 15 min to completely dissolve the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and ultrasonically disperse for 15 min to completely disperse 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. The solution was degassed by freezing / thawing with liquid nitrogen three times for deoxygenation and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature, and the product was collected by centrifugation and washed several times with tetrahydrofuran, dried in a 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 in 10 mL of methanol and disperse them ultrasonically 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 it with methanol several times, dry it in vacuum at 60 ° C for 12 h, and grind it into powder (brown powder) to obtain Si@COF-Co.

[0072] (6) Perform thermogravimetric analysis on the Si@COF material to obtain the silicon content in the material, such as Figure 3 As shown in the figure, the temperature range is 30-900℃ at a heating rate of 10℃ / min in air atmosphere. It can be seen from the figure that in the range of 350-650℃, the material undergoes thermal decomposition, mainly the protective layer porphyrin COF decomposition, and the mass increases after 650℃. This is because the oxidation temperature of silicon is reached, resulting in partial oxidation of silicon to form silicon dioxide. Analysis shows that the silicon content in the material is 89.49%.

[0073] Example 6: Using porphyrin COF as a nano-silicon conductive nano-protective layer to construct Si@COF-Co material

[0074] (1) Weigh 200 mg of nano-silicon (50-100 nm) and add it to 10 mL of methanol. Ultrasonicate for more than 30 min 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 20 mg / mL.

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

[0076] (3) 1 mL of PEI methanol solution was slowly added dropwise to the methanol solution of silicon, and the mixed solution was stirred at room temperature for 2 h at a stirring speed of 600 r / min. The mixed solution was then centrifuged and washed four times with anhydrous ethanol. The obtained brown solid was dried at 60°C for 12 h. The obtained product was ground into powder and stored in a desiccator to obtain powdered PEI-modified nanosilicon (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, and disperse them by ultrasonication for 15 min to completely dissolve the solid. Then add 15 mg of 2,5-dihydroxyterephthalaldehyde (DHA) and 8.2 mg of 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin (TPH), and disperse them by ultrasonication for 15 min to completely disperse the solid. Then 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. The solution was degassed by freezing / thawing with liquid nitrogen three times for deoxygenation and then heated at 120 ° C for 72 h. After the reaction, the solution was cooled to room temperature and then centrifuged to collect the product. The product was washed several times with tetrahydrofuran, dried in a 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 in 5 mL of methanol, and ultrasonically disperse 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 it with methanol several times, dry it in vacuum 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 test system. Figure 7 As shown in Figure 2, Si@COF-Co material has a high current density of 1000 mA g -1 After 500 cycles, it can maintain 2099.4mAh·g-1 The discharge capacity of pure silicon (such as Figure 8 ) found that the performance of pure nano-silicon decayed rapidly, indicating that the Si@COF-Co material has excellent cycle performance, and the porphyrin COF protective layer can effectively inhibit the volume expansion of nano-silicon, thereby maintaining the stability of the battery material performance.

[0080] In general, scanning electron microscopy ( Figure 1 ) shows that the material has a uniform spherical morphology. High-resolution transmission electron microscopy ( Figure 2 ) shows that there is a stable porphyrin COF layer in Si@COF-Co, and the composite material has obvious lattice fringes, which correspond to the (111) crystal plane of silicon. TGA curve ( Figure 3 ) shows that silicon accounts for a large proportion of the silicon protective layer material. Raman spectrum ( Figure 4 ) shows the presence of strong characteristic peaks of silicon. EIS spectrum ( Figure 5 ), cyclic voltammetry curve ( Figure 6 ), cycle performance curve ( Figure 7 ) and compared with pure silicon cycle performance ( Figure 8 ) showed that Si@COF-Co significantly improved the conductivity of silicon and the cycling performance at high current density.

[0081] The embodiments of the present invention are 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 of these embodiments are made without departing from the principles and spirit of the present invention, and still fall within the protection scope of the present invention.

Claims

1. A method for constructing Si@COF-Co material using porphyrin COF as a nano-silicon conductive nano-protective layer, characterized in that: The following steps are involved: S1, mixing the nano-silicon methanol solution with the polyethyleneimine PEI methanol solution, stirring at room temperature and then washing with ethanol to obtain a brown solid, and then drying and grinding into powder to obtain powdery PEI-modified nano-silicon Si-PEI; S2, dispersing Si-PEI and polyvinyl pyrrolidone in a mixed solution of o-dichlorobenzene / n-butanol, adding monomers 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin and 2,5-dihydroxyterephthalaldehyde, adding glacial acetic acid after dissolution and stirring at room temperature; S3, adding glacial acetic acid to the mixed solution obtained in step S2, reacting at 110-130° C. for 70-80 hours after degassing and deoxygenation, washing, drying, and grinding into powder after the reaction to obtain Si@COF; S4. Disperse Si@COF and cobalt acetate tetrahydrate in methanol, stir at room temperature, collect the product, wash, dry, and grind into powder to obtain Si@COF-Co.

2. The method of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer 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 of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer according to claim 1, characterized in that: In S1, the stirring time at room temperature is 1-4 hours, and the rotation speed is 500-1000 r / min; in S2, the stirring time at room temperature is 3-6 hours, and the rotation speed is 300-600 r / min; in S4, the stirring time at room temperature is 10-15 hours, and the rotation speed is 500-800 r / min.

4. The method of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer according to claim 1, characterized in that: In S2, the mass ratio of Si-PEI, polyvinylpyrrolidone, 5,10,15,20-tetrakis(4-aminophenyl)-21H,23H-porphyrin, and 2,5-dihydroxyterephthalaldehyde is 590-610:490-510:40-43:73-77; the concentration of Si-PEI in the o-dichlorobenzene / n-butanol mixture is 6 mg / 1-2 mL.

5. The method of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer according to claim 1, characterized in that: In the o-dichlorobenzene / n-butanol mixed solution of S2, the volume ratio of o-dichlorobenzene to n-butanol is 1:

1.

6. The method of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer according to claim 1, characterized in that: The concentration of glacial acetic acid in S2 and S3 is 5-7M, wherein the amount of S2 is 350-450uL per 120mg Si-PEI; the amount of S3 is 550-650uL per 120mg Si-PEI.

7. The method of constructing Si@COF-Co material using porphyrin COF as nano-silicon conductive nano-protective layer 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. Si@COF-Co material prepared by the method according to any one of claims 1 to 7 using porphyrin COF as a nano-silicon conductive nano-protective layer.

9. Application of Si@COF-Co material prepared by the method according to any one of claims 1 to 7 with porphyrin COF as nano-silicon conductive nano-protective layer in the field of energy storage.

10. The use according to claim 9, characterized in that: The Si@COF-Co material is applied to negative electrode materials of lithium-ion batteries.

Images