A porous silicon-carbon negative electrode material based on a silicon aerogel structure and a preparation method thereof

Abstract

The application discloses a preparation method of a porous silicon-carbon negative electrode material based on a silicon aerogel structure, and the preparation method comprises the following steps: uniformly stirring and configuring tetraethyl orthosilicate, ethanol, deionized water, glucose and hexadecyl trimethyl ammonium bromide into an A solution, uniformly mixing and configuring resorcinol and formaldehyde into a B solution, the mass ratio of the resorcinol to the tetraethyl orthosilicate being 1:5-20, adding dilute hydrochloric acid into the A solution to adjust the pH value to 2, mixing the A solution with the B solution, then adding ammonia water to adjust the pH value to 7-8, and then adding anhydrous ethanol for immersion after standing, and finally performing vacuum freeze drying and high-temperature reduction carbonization treatment to obtain the porous silicon-carbon negative electrode material. The application further discloses the porous silicon-carbon negative electrode material based on the silicon aerogel structure. The silicon-carbon composite three-dimensional nano porous structure is prepared by regulating and controlling the tetraethyl orthosilicate and the phenolic resin to jointly gel, the organic carbon material is introduced while the porous structure is constructed, the process of carbon compounding is simplified, and the conductivity of the material is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of materials, in particular to a porous silicon-carbon negative electrode material based on a silicon aerogel structure and a preparation method thereof. BACKGROUND

[0002] The rapid development of the world economy and technology since the twenty-first century has led to an increasing demand for energy in human society, and lithium-ion batteries are one of the most widely used energy storage elements. The low specific capacity (372 mA h g -1 ) of the current commercial graphite anode has been unable to meet the growing demand. Among all potential lithium-ion battery anodes, silicon (Si) is one of the most promising candidate materials to replace graphite, with a theoretical specific capacity of 4200 mA h g -1 , but the huge volume expansion (~300%) during lithium extraction and insertion hinders its practical application. Compared with elemental silicon, silicon monoxide SiO x (x = 0-2) as an anode material has a theoretical capacity of 1600-2000 mA h g -1 , both of which are higher than most anode materials, and the raw material price is relatively lower than that of pure Si, and the generation of multiple electrochemically inert phases during lithium extraction and insertion in SiO x results in a much smaller volume change than pure Si material, making it an ideal choice for anode materials. However, SiO x as an anode material also has some key problems, such as low first coulombic efficiency and poor electrical conductivity, which limit the application of SiO x anode materials. In view of these problems, researchers currently mainly improve the electrochemical performance through material compounding and structure design.

[0003] The existing technology uses an organic pyrolytic carbon buffer layer, which can provide part of the space required for expansion and to some extent reduce the structural damage caused by the volume effect of the silicon core, but the research process is relatively complex, the raw materials are relatively expensive, and the use of magnesium heat method, hydrothermal method, and multiple calcination method requires high production equipment, which is not conducive to promoting the commercialization process of silicon-based materials. SUMMARY

[0004] In order to overcome the deficiencies of the above prior art, the purpose of the present application is to provide a preparation method of a porous silicon-carbon anode material based on a silicon aerogel structure, which avoids complex process routes and high preparation costs, and solves the problems of low first coulombic efficiency and poor electrical conductivity of silicon monoxide as an anode material.

[0005] Another purpose of the present application is to provide a porous silicon-carbon anode material based on a silicon aerogel structure.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A preparation method of a porous silicon-carbon negative electrode material based on a silicon aerogel structure, the specific steps are as follows:

[0008] (1) Take tetraethyl orthosilicate, ethanol, deionized water, glucose and cetyltrimethylammonium bromide, and uniformly stir to prepare an A solution, and take resorcinol and formaldehyde, and mix to prepare a B solution, wherein the mass ratio of resorcinol to tetraethyl orthosilicate is 1:6-20;

[0009] (2) Add dilute hydrochloric acid to the A solution to adjust the pH value to 1.5-2.5, mix it with the B solution, then add ammonia water to adjust the pH value to 7-8, and then soak in anhydrous ethanol after standing to obtain a SiO2 / gl / RF composite gel;

[0010] (3) The SiO2 / gl / RF composite gel is prepared by vacuum freeze-drying to prepare a SiO2 / gl / RF composite powder; the SiO2 / gl / RF composite powder is subjected to high-temperature reduction and carbonization treatment in an argon-hydrogen atmosphere to obtain a porous silicon-carbon negative electrode material SiO2 / gl-C / RF-C. x / gl-C / RF-C.

[0011] Preferably, the specific steps of the high-temperature reduction and carbonization treatment are as follows:

[0012] The SiO2 / gl / RF composite powder is heated to 350-450℃ and kept for 0.5-1.5h, and then continuously heated to 800-1000℃ and kept for 1.5-2.5h.

[0013] Preferably, the heating is carried out at a heating rate of 4-6℃ / min.

[0014] Preferably, in step (2), the anhydrous ethanol is replaced every 10-12h, and the soaking is carried out for 48-72h.

[0015] Preferably, the volume ratio of the tetraethyl orthosilicate to the ethanol is 1:5-15, the volume ratio of the tetraethyl orthosilicate to the deionized water is 5:1-4, and the mass ratio of the tetraethyl orthosilicate to the glucose is 1-2:1.

[0016] Preferably, the molar ratio of the resorcinol to the formaldehyde is 1:1-4.

[0017] Preferably, the mass of the cetyltrimethylammonium bromide is 0.01-0.1g.

[0018] Preferably, the mass ratio of the cetyltrimethylammonium bromide to the deionized water is 1:30-50.

[0019] Preferably, the concentration of the dilute hydrochloric acid is 0.05-0.15 mol / L.

[0020] Preferably, the concentration of the ammonia water is 0.1-1 mol / L.

[0021] Preferably, the composition of the argon-hydrogen atmosphere is 92-95% argon and 5-8% hydrogen.

[0022] Preferably, the time for vacuum freeze drying is 60-84 h, and the vacuum degree is 20-50 Pa.

[0023] Preferably, the SiO2 / gl / RF composite powder is orange-red.

[0024] Preferably, in step (2), after adding the dilute hydrochloric acid, the hydrolysis time is 1.5-2.5 h.

[0025] Preferably, in step (2), the temperature for standing is 23-30℃, and the standing time is 18-30 h.

[0026] A porous silicon-carbon negative electrode material based on a silicon aerogel structure is prepared by the preparation method of the porous silicon-carbon negative electrode material based on a silicon aerogel structure.

[0027] The present application has the following advantages and beneficial effects compared with the prior art:

[0028] 1) The present application provides a porous silicon-carbon negative electrode material based on a silicon aerogel structure and a preparation method, which completes the reduction of silicon dioxide, carbon coating and nano-mesoporous structure design in one pot in one step, and the obtained silicon-carbon composite material not only has a high specific surface area, a first coulombic efficiency of 70.64%, a high first charge-discharge specific capacity, good conductivity performance and is environmentally friendly.

[0029] 2) The present application prepares a silicon-carbon composite three-dimensional nano-porous structure by regulating the co-gelation of tetraethyl orthosilicate and phenolic resin, wherein glucose is used as a carbon source and reducing agent for the external carbon layer of the porous structure, and the use of glucose is safer and greener and has no pollution compared with the traditional metal magnesium reducing agent; phenolic resin is used as a carbon source for the internal conductive carbon layer of the porous structure, and the nano-sized silicon particles and the surrounding composite carbon material help to alleviate the volume expansion of silicon; by regulating the ratio between tetraethyl orthosilicate and resorcinol, the composite degree of the carbon component in the material is regulated, and a porous silicon-carbon composite material with an optimal carbon content is prepared. The porous structure of the material increases the contact area of the electrolyte, improves the ion transmission efficiency, and also provides a strong buffer space for the volume expansion of silicon. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1XRD patterns of the silicon-carbon composite material prepared in Example 1 before and after heat treatment and the silicon-carbon composite material prepared in Comparative Example 1 after heat treatment.

[0031] Figure 2 SEM images of the silicon-carbon composite materials prepared in Examples 1-3 and Comparative Example 1, wherein a is the SEM image of the silicon-carbon composite material prepared in Example 1, b is the SEM image of the silicon-carbon composite material prepared in Example 2, c is the SEM image of the silicon-carbon composite material prepared in Example 3, and d is the SEM image of the silicon-carbon composite material prepared in Comparative Example 1.

[0032] Figure 3 Raman spectra of the silicon-carbon composite materials prepared in Comparative Example 1 and Example 1.

[0033] Figure 4 N2 adsorption / desorption isotherms and pore size distribution of the silicon-carbon composite materials prepared in Example 1 and Comparative Example 1, wherein a is the N2 adsorption / desorption isotherm and b is the pore size distribution.

[0034] Figure 5 Cycle performance comparison of the silicon-carbon composite materials prepared in Examples 1, 2, 3 and Comparative Example 1 at a current density of 100 mA / g.

[0035] Figure 6 Si element fine XPS spectra of the silicon-carbon composite materials prepared in Comparative Example 2 and Example 1, wherein a is the fine spectrum of the Si element after peak separation of Comparative Example 2, and b is the fine spectrum of the Si element after peak separation of Example 1.

[0036] Figure 7 Structure of the porous silicon-carbon negative electrode material based on the structure of a silica aerogel. DETAILED DESCRIPTION

[0037] The inventive purpose of the present application will be further described in detail below in combination with the drawings and specific examples. The examples cannot be described one by one here, but the embodiments of the present application are not limited to the following examples.

[0038] Example 1

[0039] Resorcinol and formaldehyde were mixed to form solution B, with a molar ratio of resorcinol to formaldehyde of 1:2 and a mass ratio of resorcinol to TEOS of 1:20. Solution A was prepared by uniformly stirring TEOS, ethanol, deionized water and glucose for 30 min, with a volume ratio of TEOS, ethanol and water of 5:50:2, a mass ratio of TEOS to glucose of 1.4:1 and a mass ratio of CTAB to water of 1:40. Solution A was added dropwise to 0.1 mol / L dilute hydrochloric acid until the pH was 2, and hydrolysis was performed under magnetic stirring for 2 h. After hydrolysis, solutions A and B were mixed, and 0.5 mol / L ammonia water was added dropwise to adjust the pH to 7-8, and condensation was performed under magnetic stirring. After the solution became a gel, stirring was stopped, and the gel was left to stand at room temperature for 24 h to complete the gelation process. The gel was transferred to a beaker for solvent replacement, and was soaked in anhydrous ethanol, which was replaced every 12 h. After 48 h, SiO2 / gl / RF composite gel was obtained. The prepared gel was rapidly frozen with liquid nitrogen and then placed in a freeze dryer for vacuum freeze-drying treatment. After 72 h, SiO2 / gl / RF composite powder was obtained. The SiO2 / gl / RF composite powder was placed in a corundum boat in a tube furnace, heated to 900°C at a rate of 5°C / min under an argon-hydrogen mixed atmosphere (hydrogen content 8%) and held for 2 h, and then cooled to room temperature to obtain the negative electrode material (SiO2 / gl-C / RF-C-0.5). The structural diagram is shown in FIG. 1. x / gl-C / RF-C-0.5);its structural diagram is shown in FIG. 1. Figure 7

[0040] Half-cell assembly and performance characterization: The silicon-carbon composite material prepared in Example 1 was ground with conductive agent acetylene black and binder PVDF at a mass ratio of 8:1:1, and NMP organic solvent was slowly added during the grinding process to form a uniform electrode slurry, which was then coated on the surface of a copper foil current collector. After vacuum drying, punching and pressing, a negative electrode sheet was obtained. The prepared negative electrode sheet was placed in a glove box, and a button cell (CR2016) was assembled in the glove box using the active electrode, a separator and a lithium sheet as the counter electrode, and positive and negative electrode shells. The cycle performance test conditions of the assembled battery were as follows: 100 cycles at a current density of 100 mA / g and a voltage range of 0.01-3 V. The test results are shown in Table 1.

[0041] Example 2

[0042] ​Resorcinol and formaldehyde were mixed to form solution B, with a resorcinol to formaldehyde molar ratio of 1:2 and a resorcinol to TEOS mass ratio of 1:10. Solution A was added dropwise with 0.1 mol / L dilute hydrochloric acid until the pH reached 2, and hydrolysis was performed under magnetic stirring for 2 h. After hydrolysis, solutions A and B were mixed, and 0.5 mol / L ammonia was added dropwise to adjust the pH to 7-8, and condensation was performed under magnetic stirring. After the solution became a gel, stirring was stopped, and the gel was left to stand at room temperature for 24 h to complete the gelation process. The gel was transferred to a beaker for solvent replacement, and was soaked in anhydrous ethanol, which was replaced every 12 h. After 48 h, a SiO2 / gl / RF-1 composite gel was obtained. The prepared gel was rapidly frozen with liquid nitrogen and then placed in a freeze dryer for vacuum freeze-drying treatment. After 72 h, a SiO2 / gl / RF-1 composite powder was obtained. The SiO2 / gl / RF-1 composite powder was placed in a corundum boat in a tube furnace, and heated to 900°C at a rate of 5°C / min under an argon-hydrogen mixed atmosphere (hydrogen content 8%) and held for 2 h. The furnace was then cooled to room temperature to obtain the negative electrode material, which is denoted as SiO2 / gl-C / RF-C-1 in the accompanying drawings. x / gl-C / RF-C-1.

[0043] The battery assembly method and performance characterization conditions were the same as in Example 1, and the test results are shown in Table 1.

[0044] Example 3

[0045] Resorcinol and formaldehyde were mixed to form solution B, wherein the molar ratio of resorcinol to formaldehyde was 1:2, and the mass ratio of resorcinol to TEOS was 1:5; 0.1 mol / L dilute hydrochloric acid was added dropwise to solution A until the pH was 2, and hydrolysis was performed under magnetic stirring for 2 h; after the hydrolysis was completed, solutions A and B were mixed, 0.5 mol / L ammonia water was added dropwise to adjust the pH to 7-8, and condensation reaction was performed under magnetic stirring; after the solution became a gel, stirring was stopped, and the gel was left to stand at room temperature for 24 h to complete the gelation process. The gel was transferred to a beaker for solvent replacement, and was immersed in anhydrous ethanol, which was replaced every 12 h. After 48 h, SiO2 / gl / RF-2 composite gel was obtained; the prepared gel was rapidly frozen with liquid nitrogen and then placed in a freeze dryer for vacuum freeze-drying treatment, and after 72 h, SiO2 / gl / RF-2 composite powder was obtained; the prepared SiO2 / gl / RF-2 composite powder was placed in a corundum boat in a tube furnace, heated to 900°C at a rate of 5°C / min under an argon-hydrogen mixed atmosphere (hydrogen content 8%) and held for 2 h, and then cooled to room temperature to obtain a negative electrode material, which is denoted as SiO2 / gl-C / RF-C-2 in the accompanying drawings. x / gl-C / RF-C-2.

[0046] The battery assembly method and performance characterization conditions were consistent with those of Example 1, and the test results are shown in Table 1.

[0047] Comparative Example 1:

[0048] The TEOS, ethanol, deionized water and glucose were measured according to certain proportion, stirred uniformly for 30 min to mix and configure into solution, and CTAB was added as dispersant, wherein the volume ratio of TEOS: ethanol: water = 5: 50: 2, the mass ratio of TEOS: glucose = 1.4: 1, and the mass ratio of CTAB to water is 1: 40; 0.1 mol / L dilute hydrochloric acid was added dropwise into the mixed solution until PH = 2, and hydrolysis was carried out under magnetic stirring for 2 h; 0.5 mol / L ammonia water was added dropwise into the solution after hydrolysis to adjust the PH to 7-8, and condensation reaction was carried out under magnetic stirring; after the solution became gel completely, the stirring was stopped, and the gel was placed at room temperature for 24 h to complete the gel process. The gel was transferred to a beaker for solvent replacement, soaked with anhydrous ethanol, and the ethanol was replaced every 12 hours. After 48 h, SiO2 / gl / RF-3 composite gel was obtained; the prepared gel was rapidly frozen with liquid nitrogen and then placed in a freeze dryer for vacuum freeze-drying treatment, and SiO2 / gl / RF-3 composite powder was obtained after 72 h.

[0049] The SiO2 / gl / RF composite powder corundum ceramic boat was placed in a tube furnace, heated to 900℃ at a heating rate of 5℃ / min under argon-hydrogen mixed gas atmosphere (hydrogen content 8%) and kept for 2 h, and then cooled to room temperature to obtain the negative electrode material, which is recorded as SiO2 / gl / RF-C in the drawing. x / gl-C.

[0050] The battery assembly method and performance characterization conditions were consistent with those of Example 1, and the test results are shown in Table 1.

[0051] Comparative Example 2

[0052] The tetraethyl orthosilicate (TEOS), ethanol, deionized water were measured by a certain proportion, stirred uniformly for 30 min to mix and configure into a solution, and CTAB was added as a dispersant, wherein the volume ratio of tetraethyl orthosilicate: ethanol: water = 5: 50: 2, and the mass ratio of CTAB to water is 1:40; 0.1 mol / L dilute hydrochloric acid was added dropwise to the mixed solution until PH = 2, and hydrolysis was carried out under magnetic stirring for 2 h; 0.5 mol / L ammonia water was added dropwise to the solution after hydrolysis to adjust the PH to 7-8, and the condensation reaction was carried out under magnetic stirring; after the solution became a gel state, the stirring was turned off, and the gel was placed at room temperature for 24 h to complete the gel process. The gel was transferred to a beaker for solvent replacement, soaked with anhydrous ethanol, and the ethanol was replaced every 12 hours. After 48 h, SiO2 / RF composite gel was obtained; the prepared gel was rapidly frozen with liquid nitrogen and then placed in a freeze dryer for vacuum freeze-drying treatment, and SiO2 / RF composite powder was obtained after 72 h; the SiO2 / RF composite powder was placed in a corundum ceramic boat in a tube furnace, heated to 900℃ at a heating rate of 5℃ / min under an argon-hydrogen mixed atmosphere (hydrogen content 8%) and held for 2 h, and then cooled to room temperature to obtain the negative electrode material (SiO2 / RF-C).

[0053] The battery assembly method and performance characterization conditions were consistent with those of Example 1, and the test results are shown in Table 1.

[0054] The silicon-carbon composite materials prepared in Examples 1-3 and Comparative Examples 1-2 were assembled into batteries and tested for performance, and the test results are shown in Table 1:

[0055] Table 1

[0056]

[0057] The BET specific surface area of the SiO2 / RF-C materials was calculated by the BET method, and the results are shown in Table 2. x The BET specific surface area of the SiO2 / RF-C materials was calculated by the BET method, and the results are shown in Table 2.

[0058] Table 2

[0059]

[0060] According to Table 1, as the amount of resorcinol (R) added increases, the first discharge specific capacity of the material decreases, which is due to the increase in the proportion of carbon components in the material, resulting in a decrease in the proportion of high-capacity silicon components, thereby reducing the first discharge capacity. When the mass ratio of resorcinol to tetraethyl orthosilicate is 1:20, the first discharge capacity of the material is very close to that without adding resorcinol (R), but the first coulombic efficiency of the material is improved, because a small amount of resorcinol (R) pyrolytic carbon components are evenly distributed in the interior of the three-dimensional gel structure, avoiding the aggregation of SiO2 / RF-C materials during the first charge-discharge process, and the first coulombic efficiency is improved. xDirect contact with electrolyte reduces the irreversible Li + consumption, while increasing the conductivity of the material. With the increase of resorcinol (R), the first coulombic efficiency of the electrode material does not improve. Therefore, when the ratio between tetraethyl orthosilicate and resorcinol is moderate, the degree of carbon component compounding in the material can be regulated to prepare a porous silicon-carbon composite material with the best carbon content.

[0061] The BET specific surface area of SiO x The BET specific surface area of SiO

[0062] Figure 1 The XRD patterns of the silicon-carbon composite materials prepared in Example 1 before and after heat treatment and the silicon-carbon composite material prepared in Comparative Example 1 after heat treatment are shown in Figure 2, wherein Figure 2a is the XRD pattern of the silicon-carbon composite material prepared in Example 1 before heat treatment, Figure 2b is the XRD pattern of the silicon-carbon composite material prepared in Example 1 after heat treatment, and Figure 2c is the XRD pattern of the silicon-carbon composite material prepared in Comparative Example 1 after heat treatment. Figure 1 It can be seen that the sharp peak of the SiO2 / gl / RF sample before heat treatment at about 21° is the characteristic peak of glucose crystal, which proves that glucose is successfully added to the material. In addition to the characteristic peak of glucose, the three samples in the region of 18-25° all show only one steamed bun peak structure, which corresponds to amorphous SiO2. This indicates that the silicon in the composite material prepared by the sol-gel method and the freeze-drying method is amorphous. After heat treatment, the sample does not have a relatively obvious carbon peak at 43°, because the pyrolysis carbon of glucose is also an amorphous structure, and the steamed bun peak position overlaps with the peak position of amorphous silicon dioxide.

[0063] Figure 2 The SEM images of the silicon-carbon composite materials prepared in Examples 1-3 and Comparative Example 1 are shown in Figure 3, wherein Figure 3a is the SEM image of the silicon-carbon composite material prepared in Example 1, Figure 3b is the SEM image of the silicon-carbon composite material prepared in Example 2, Figure 3c is the SEM image of the silicon-carbon composite material prepared in Example 3, and Figure 3d is the SEM image of the silicon-carbon composite material prepared in Comparative Example 1. Figure 2It can be seen that: when the amount of resorcinol (R) added is small, the morphology of the material after compounding with phenolic resin is not much different from that before compounding, and it still presents a structure similar to aerogel, which is composed of particles with a particle size of less than 50nm. The formed accumulation pores are obvious, and there is agglomeration between the particles. Since the phenolic resin also undergoes a solvent gel reaction during the preparation process, its gel network and the SiO2 gel network are interspersed and cross-linked, and a thin carbon layer is formed inside the gel network after heat treatment. Figure 2 From the comparison of Figures (a) and (b), it can be seen that after adding resorcinol (R), the particles appear more dispersed and the fusion phenomenon between nanoparticles is reduced. This may be because the carbon compounded in the network structure plays a certain supporting role in the mesopores and can separate the silicon particles on both sides of the pores, thereby alleviating the collapse of the silica gel network structure and the fusion phenomenon of the particles at high temperatures. When the mass ratio of resorcinol to ethyl orthosilicate is 1:20, the material forms a SiO x The particles are stacked and coated with amorphous carbon on both the inside and outside of the three-dimensional mesoporous structure. The larger number of pores in this structure is conducive to the infiltration of the electrolyte and the transmission of lithium ions. The carbon coated on the inner and outer layers also helps to improve the conductivity of the material. As the amount of phenolic resin added increases, the carbon content of the material increases, the pores between the particles in the SiO2 gel are gradually filled with amorphous carbon, the pores of the material gradually decrease, and the agglomeration phenomenon becomes increasingly serious. When the mass ratio of resorcinol to ethyl orthosilicate is 1:5, the pores inside the material are almost completely filled with carbon. At this time, the contact between silicon and lithium ions and the infiltration of the electrolyte during the lithium insertion process will become extremely difficult, and the electrochemical performance of the material will also decline with the disappearance of the porous structure.

[0064] Figure 3 The Raman spectra of the silicon-carbon composite materials prepared in Example 1 and Comparative Example 1 are shown in FIG. Figure 3 From the curve, we can see that at a wavelength of 1330cm -1 and 1600cm -1 There are two strong characteristic peaks, which correspond to the D-peak (amorphous state) and G-peak (graphitized state) of carbon materials. The relative intensity value between the D peak and the G peak (I D / I G ) is used to characterize the degree of defects in carbon materials. The larger the ratio, the greater the degree of defects. x / gl-C and SiO x / gl-C / RF-C-0.5 material corresponding to I D / I G The values ​​are 2.29 and 2.68 respectively, indicating that the carbon formed by the pyrolysis of glucose and phenolic resin at 900℃ is an amorphous carbon material. x / gl-C and SiO x / gl-C / RF-C-0.5 composite material corresponding to I D / I G It can be seen that the addition of phenolic resin can effectively improve the defect degree of carbon materials in the material, and the related electrical performance test also proves that this defect-rich structure is more conducive to the rapid conduction of electrons, so that the electrode material has more excellent cycle performance.

[0065] Figure 4 The N2 adsorption / desorption isotherm and pore size distribution of the silicon-carbon composite material prepared in Example 1 and Comparative Example 1 are shown in FIGS. 1 and 2, respectively. Figure 4 It can be seen that the SiO x / gl-C and SiO x The nitrogen adsorption / desorption curves of the / gl-C / RF-C-0.5 composite material all have obvious inflection points at 0.5, and are all type IV adsorption isotherms; and there are obvious H2(a) type hysteresis loops in the high pressure region of 0.4-0.9, which conforms to the hysteresis loop characteristics of silica gel type ordered three-dimensional mesoporous materials. The pore size distribution obtained by BJH method can be seen from the pore size distribution, which is about 3.5 nm. These small mesopores are derived from the mesoporous structure of the part of silica gel remaining after vacuum freeze drying.

[0066] Figure 5 The cycle performance comparison chart of the silicon-carbon composite materials prepared in Examples 1-3 and Comparative Example 1 at a current density of 100 mA / g is shown in FIG. 3. Figure 5 It can be seen that the material without adding resorcinol (R) has a remaining reversible capacity of 478 mAh g -1 after 100 cycles, and the capacity retention rate is 60.81%; when the mass ratio of resorcinol and tetraethyl orthosilicate is 1:20 and 1:10, the remaining reversible capacity of the electrode material is 551 mAh g -1 and 507 mAh g -1 , respectively, and the reversible capacity retention rate is 66.23% and 80.73%. The average coulombic efficiency from the 2nd cycle to the 100th cycle is more than 99%. This shows that the addition of a certain amount of resorcinol (R) component improves the electrical conductivity of the material by coating a thin carbon layer inside the accumulated pore; at the same time, it also improves the internal strength of the gel network structure, alleviates the volume expansion of SiO x inside, thereby improving the cycle performance of the material. When the mass ratio of resorcinol and tetraethyl orthosilicate is 1:5, the cycle stability of the material is also partially improved, with a capacity retention rate of 63.25%, but the reversible capacity is only 389 mAh g -1 after 100 cycles, which further shows that the addition of carbon content in the silicon-carbon negative electrode can both reflect the capacity advantage of silicon materials and inhibit the expansion of silicon materials and improve the electrical conductivity of the system.

[0067] Figure 6 The Si element XPS spectra of the silicon-carbon composite materials prepared in Example 1 and Comparative Example 2 are shown, where a is the Si element spectra after peak separation in Comparative Example 2, and b is the Si element spectra after peak separation in Example 1. Figure 5 It can be seen that: Si 0 The corresponding binding energy is 99.74eV, Si 1+ 100.39eV, Si 2+ 101.83eV, Si 3+ 102.96eV, Si 4+ The SiO2 / RF-C sample without glucose was not reduced, and the valence state of Si was all +4. x After peak fitting, the / gl-C / RF-C-0.5 sample clearly has peaks of +2 and +3 valences, and the peak area of ​​+2 valence accounts for the largest proportion, which indicates that the Si in this sample has been partially reduced and the average valence state is close to +2.

[0068] The above specific implementation manner is a preferred embodiment of the present invention and does not limit the present invention. Any other changes or other equivalent replacement methods that do not deviate from the technical solution of the present invention are included in the protection scope of the present invention.

Claims

1. A method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure, characterized in that: The specific steps are as follows: (1) Ethyl orthosilicate, ethanol, deionized water, glucose and hexadecyltrimethylammonium bromide were uniformly stirred to prepare solution A, and resorcinol and formaldehyde were mixed to prepare solution B, wherein the mass ratio of resorcinol to ethyl orthosilicate was 1:20; (2) Add dilute hydrochloric acid to the solution A to adjust the pH value to 1.5-2.5, mix it with the solution B, then add ammonia water to adjust the pH value to 7-8, let it stand and then add anhydrous ethanol to soak, to obtain SiO2 / gl / RF composite gel; (3) The SiO2 / gl / RF composite gel is subjected to vacuum freeze drying to prepare SiO2 / gl / RF composite powder; the SiO2 / gl / RF composite powder is subjected to high temperature reduction carbonization treatment in an argon-hydrogen atmosphere to prepare SiO2 / gl / RF composite powder. x Porous silicon-carbon anode material SiO with three-dimensional mesoporous structure and amorphous carbon coating on both the inside and outside of the particles x / gl-C / RF-C.

2. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The specific steps of the high-temperature reduction carbonization treatment are as follows: The SiO2 / gl / RF composite powder is heated to 350-450°C and kept warm for 0.5-1.5 hours, and then continued to be heated to 800-1000°C and kept warm for 1.5-2.5 hours.

3. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 2, characterized in that: The heating is specifically carried out at a heating rate of 4-6°C / min.

4. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The volume ratio of the ethyl orthosilicate to the ethanol is 1:5-15, the volume ratio of the ethyl orthosilicate to the deionized water is 5:1-4, and the mass ratio of the ethyl orthosilicate to the glucose is 1-2:

1.

5. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The molar ratio of resorcinol to formaldehyde is 1:1-4.

6. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The concentration of the dilute hydrochloric acid is 0.05-0.15 mol / L.

7. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The concentration of the ammonia water is 0.1-1 mol / L.

8. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The composition of the argon-hydrogen atmosphere is 92-95% argon and 5-8% hydrogen.

9. The method for preparing a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to claim 1, characterized in that: The vacuum freeze drying time is 60h-84h, and the vacuum degree is 20-50Pa.

10. A porous silicon-carbon negative electrode material based on a silicon aerogel structure, characterized in that: It is prepared by the preparation method of a porous silicon-carbon negative electrode material based on a silicon aerogel structure according to any one of claims 1 to 9.

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