A method for preparing high-purity sol, silica sol prepared by the method and its use

Abstract

This invention discloses a method for preparing high-purity, highly monodisperse silica sol. Using amino acids as catalysts to adjust the solution pH, catalyze the hydrolysis of silicon powder, and control the SiO2 particle morphology, this method allows for the controlled production of highly monodisperse nano-SiO2 with varying particle sizes. The silica sol produced by this method can be widely used in fields such as catalyst supports and battery anode materials. The monodisperse silica particles prepared by this method are mixed with a sugar solution, spray-dried, and calcined to produce carbon-coated silica particles. These particles can then be used as battery anodes, exhibiting excellent electrochemical performance.

Description

Technical Field

[0001] The present invention relates to the technical field of silica sol preparation, and in particular to a method for preparing high-purity silica sol, the silica sol prepared by the method and applications thereof. Background Art

[0002] Silica sol is a dispersion of nanometer-sized silica particles in water or a solvent. The particle size can range from 5 to 120 nm. Because the SiO2 in silica sol contains a large amount of water and hydroxyl groups, silica sol can also be expressed as mSiO2·nH2O. Due to the high number of hydroxyl groups on the surface of the silica particles in silica sol, silica sol has high reactivity and is therefore widely used in the chemical industry, electronics, coatings, food, mineral processing and other fields.

[0003] Silicon dioxide (SiO2) material has a high theoretical capacity (1965mAh g -1 ), smaller volume expansion (100%) than silicon, and abundant reserves make it considered a promising lithium battery negative electrode material. However, due to its low conductivity, it is usually coated with a carbon layer to enhance its conductivity. Research has found that small, monodisperse SiO2 particles have a larger specific surface area and active range. The uniform carbon coating helps provide more reactive sites, thereby improving material utilization and providing higher capacity.

[0004] However, some special industries, such as nano-silica carriers used for synthesizing acrylonitrile catalysts, also require high purity of silica sol, that is, low metal ion content and good stability; at the same time, the nano-SiO2 particles in the silica sol are required to have good size monodispersity. If the particle size distribution is too wide, the small-sized SiO2 particles will fill the pores formed by the accumulation of large-sized SiO2 particles, resulting in a low specific surface area of ​​the catalyst, which greatly affects its catalytic activity.

[0005] There are generally three methods for preparing silica sol:

[0006] The first is the ion exchange method, which uses diluted Na2SiO3 as raw material and removes Na + 、Cl －Impurity ions such as sodium hydroxide (NaOH) and potassium hydroxide (KOH) are removed to obtain a poly-Na2SiO3 mother liquor. To improve its stability, a small amount of sodium hydroxide (NaOH) or potassium hydroxide (KOH) is generally added to adjust the pH value to a stable region. Subsequently, concentration and purification are performed to obtain the final product. The ion exchange method is currently a common method for producing low-end SiO2 sols in industry. This method has low raw material costs and a simple preparation process, making it suitable for large-scale industrial production. However, the nano-SiO2 produced has a wide particle size distribution, poor stability, and contains a large amount of impurity ions that cannot be removed. Moreover, when the anion and cation exchange resins lose their exchange capacity, they need to be regenerated with NaOH and dilute hydrochloric acid, which will produce a large amount of wastewater.

[0007] The second method is the hydrolysis of silicon alkoxide, also known as Method, which uses alkaline catalyst NH3·H2O to catalyze the hydrolysis of tetraethyl orthosilicate (TEOS). Due to the low miscibility between unhydrolyzed TEOS and water, a cosolvent (alcohol) is generally used to make them mutually soluble. Its reaction mechanism is that organic or inorganic catalysts hydrolyze silicon alkoxides, and the silanol groups undergo condensation reactions to produce siloxane bonds and by-products, namely alcohol or water. The nano-SiO2 produced by this method has a narrow particle size distribution, good monodispersity, good stability, and large particle size, which can make up for the shortcomings of the ion exchange method and can be used to produce high-quality nano-SiO2. However, this route requires the use of expensive silicon alkoxides as raw materials, and a large amount of organic solvents (such as methanol, ethanol or isopropanol, etc.). The prepared silica sol has a low solid content and high cost, making it difficult to achieve industrial application.

[0008] The third method is the elemental silicon hydrolysis method, which uses elemental silicon as the silicon source and an inorganic base (such as NaOH, KOH, water glass, etc.) as a catalyst to prepare silica sol. This method overcomes the problem of high cost of reaction raw materials in the silicon alkoxide hydrolysis method, but the inorganic base brings in metal ions, the purity is low, and the particle size distribution of the nanoparticles is wide.

[0009] Therefore, how to synthesize nano-silica with high purity, better monodispersity and low cost is an urgent problem to be solved. Summary of the Invention

[0010] One of the purposes of the present invention is to provide a method for preparing a high-purity, monodisperse, low-cost silica sol. An amino acid is used as a catalyst to adjust the pH of the solution, catalyze the hydrolysis of silicon powder, and control the morphology of SiO2 particles, thereby controllably preparing nano-SiO2 with different particle sizes and high monodispersity. Since traditional inorganic bases are not used as catalysts, the prepared silica sol has a low metal ion content. Inexpensive silicon powder is used as the raw material, and the preparation process is simple, making it easy to scale up production and effectively reducing production costs. More importantly, the amino acid not only acts as a base to catalyze the hydrolysis of metallic silicon powder, but also can hydrogen bond to the surface of the SiO2 core, controlling SiO2 growth, thereby imparting good size monodispersity to the nano-SiO2 ions.

[0011] In order to achieve the above objectives, the following technical solutions are adopted:

[0012] A method for preparing a high-purity sol comprises the following steps:

[0013] S1, activating silicon powder to obtain activated silicon powder;

[0014] S2, dissolving a basic amino acid in water to prepare a catalyst solution;

[0015] S3, adding the activated silicon powder to the catalyst solution under heating conditions, and hydrolyzing the solution to obtain a mixture of silicon powder and nano-silicon dioxide;

[0016] S4, filtering the mixed solution of silicon powder and nano-silicon dioxide, and the filtrate is high-purity silica sol.

[0017] In step S1, the silicon powder is activated by stirring the silicon powder in water at 50° C. to 100° C. for 1 to 2 hours, washing with water, filtering, and drying to obtain activated silicon powder.

[0018] The purity of the silicon powder is not less than 99%, and the particle size is 100-200 mesh.

[0019] Preferably, the basic amino acid is a combination of one or more of arginine, lysine or histidine.

[0020] Preferably, the arginine is L-arginine.

[0021] Preferably, the weight ratio of water, silicon powder and basic amino acid is 100:(8-13):(0.2-2).

[0022] Preferably, the weight ratio of water, silicon powder and basic amino acid is 100:13:(0.9-1.6).

[0023] The activated silicon powder can be added to the amino acid solution all at once or in batches, and there is no particular regulation on the addition rate.

[0024] The term "filtration" as used in the present invention refers to the operation of separating a fluid from a non-fluid through a medium under the action of gravity or other external forces. The medium includes but is not limited to filter paper, gauze, filter element, semipermeable membrane, filter screen, etc. In theory, any material with a porous structure can become a filtering medium; the filtering equipment includes but is not limited to a vacuum or decompression device, a pressurizing device, a centrifugal device, etc.

[0025] The silicon powder and nano-silicon dioxide mixture is filtered, and the filtrate is silica sol. The solid powder filtered out is the unreacted silicon powder, which can be recycled.

[0026] Preferably, in step S3, the reaction temperature is 65°C-90°C, and the reaction time is 15h-48h.

[0027] Preferably, in step S3, the reaction temperature is 75°C-90°C, and the reaction time is 20h-30h.

[0028] The solid content of silicon dioxide in the silica sol prepared by this method can reach 26.8wt%, and its solid content can be increased to 35wt% by concentration. The concentration method can adopt reverse osmosis filtration or evaporation concentration.

[0029] The evaporation concentration adopts conventional concentration methods in the art, such as evaporation concentration or concentration with water.

[0030] The second object of the present invention is to provide a high-purity silica sol prepared by the above method.

[0031] Preferably, the particle size of the monodisperse silica particles in the silica sol can be adjusted within the range of 8 nm to 30 nm, and the metal ion content is less than 50 ppm.

[0032] A third object of the present invention is to provide a method for preparing carbon-coated silica particles prepared from the above-mentioned high-purity silica sol, comprising the following steps:

[0033] In the first step, sugar is added to silica sol in a predetermined ratio to prepare a silica sugar solution;

[0034] The second step is spray drying the silicon dioxide sugar solution to prepare a powder;

[0035] The third step is to calcine the powder to obtain silicon dioxide coated with a carbon layer.

[0036] Preferably, in the first step, the sugar is α-lactose, and the mass ratio of silicon dioxide to α-lactose is 1:1.2-1:4.75.

[0037] Preferably, in the third step, the calcination conditions are: in a nitrogen atmosphere, the heating rate is (5-15) ° C min -1 , calcined at (600-1100)℃ for 6h.

[0038] The fourth object of the present invention is to provide silicon dioxide particles coated with the above carbon.

[0039] A fifth object of the present invention is to provide a battery negative electrode material comprising the carbon-coated silica particles.

[0040] Beneficial effects:

[0041] Compared with the prior art, the method for preparing high-purity silica sol of the present invention has the following beneficial effects:

[0042] 1. The preparation process is simple. Silicon powder can be added to the alkaline amino acid aqueous solution at one time without controlling the feeding rate. The alkaline amino acid acts as both a catalyst and a morphology control agent. The number of raw materials is small, and the process is easy to control.

[0043] Second, the raw material cost is low, easy to scale production, and the preparation cost is low;

[0044] 3. The preparation method is green and environmentally friendly, without producing three wastes;

[0045] 4. The prepared silica sol has good monodispersity and high purity;

[0046] 5. The particle size of silica sol particles can be controlled within the range of 8nm-30nm. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 XRD pattern of SiO2-6#;

[0048] Figure 2 (a) Transmission electron microscopy (TEM) of SiO2-6# silica sol; (b) Transmission electron microscopy (TEM) of AS-40 silica sol; (c) Transmission electron microscopy (TEM) of JN-40 silica sol.

[0049] Figure 3 (a) Malvern laser particle size distribution of SiO2-6# silica sol; (b) Malvern laser particle size distribution of AS-40 silica sol; (c) Malvern laser particle size distribution of JN-40 silica sol;

[0050] Figure 4 (a) Transmission electron microscopy characterization of SiO2-a#, (b) Malvern laser particle size distribution of SiO2-a#;

[0051] Figure 5(a) XRD patterns and (b) Raman spectra of M-SiO2@C-0, M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30;

[0052] Figure 6 TG curves of M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30;

[0053] Figure 7 (a) XPS full spectra of M-SiO2@C-0 and M-SiO2@C-10; (b) XPS silicon spectrum, (c) carbon spectrum, and (d) oxygen spectrum of M-SiO2@C-10;

[0054] Figure 8 (a)(b)(c) are SEM images of M-SiO2@C-0 at different magnifications;

[0055] Figure 9 (a) SEM image of M-SiO2@C-10; (b) SEM image of M-SiO2@C-20; (c) SEM image of M-SiO2@C-30;

[0056] Figure 10 (a) Unbroken TEM image and (b) Broken TEM image of M-SiO2@C-10; (c) HADDF-STEM image, and element distribution relative to: (d) C, (e) O, (f) Si; (g) Optical image;

[0057] Figure 11 Cyclic voltammetry curves of (a) M-SiO2@C-10, (b) M-SiO2@C-20, and (c) M-SiO2@C-30;

[0058] Figure 12 (a) M-SiO2@C-0, (b) M-SiO2@C-10, (c) M-SiO2@C-20, (d) M-SiO2@C-30 in the first cycle 20mAg -1 , followed by 50mAg -1 Charge and discharge curves at current density of ;

[0059] Figure 13 Rate performance of M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30 at different current densities;

[0060] Figure 14 Comparison of the cycling performance of M-SiO2@C-0, M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30 at 1C. DETAILED DESCRIPTION

[0061] For the convenience of understanding the present invention, the present invention is given below with examples. It should be understood by those skilled in the art that the examples are only for the purpose of helping to understand the present invention and should not be regarded as specific limitations of the present invention.

[0062] The technical concept of the present invention is to use alkaline amino acids as catalysts and morphology control agents to hydrolyze silicon powder to prepare high-purity, highly monodisperse silica sol. The monodisperse silica particles are adjustable in the range of 8nm-30nm. The solid content of the silica sol prepared in this way can reach 26.8%, and after concentration, the solid content can reach 35%.

[0063] The silicon powder in the embodiment is industrial silicon powder with a silicon content greater than 99% and a particle size of 200 mesh. Impurities in silicon powder have a direct impact on the metal ion content in the silica sol. If the metal ion content needs to be controlled within a lower range, higher quality silicon powder is required.

[0064] L-arginine is food grade, with an effective content greater than 99%.

[0065] The silicon powder activation process in the specific embodiment is as follows: 200g silicon powder is weighed and added into 240g pure water, stirred at 65°C for 2h, filtered, and the silicon powder obtained by filtration is dried in a vacuum drying oven at 65°C for 24h to obtain activated silicon powder.

[0066] Reagents or experimental methods not otherwise specified are conventional reagents or methods.

[0067] Example 1

[0068] The preparation method of silica sol in this embodiment includes the following steps:

[0069] S1, preparing activated silicon powder;

[0070] S2, dissolving 2.0 g of L-arginine in 100 g of purified water to prepare a catalyst solution;

[0071] S3, heating the catalyst solution to 65°C and adding 8g of silicon powder, and reacting for 48h to obtain a mixture of SiO2 sol and silicon powder.

[0072] S4. Filter the mixed solution through a Buchner funnel. The filtrate is the desired silica sol, named SiO2-1#.

[0073] Example 2

[0074] The preparation method of silica sol in this embodiment includes the following steps:

[0075] S1, preparing activated silicon powder;

[0076] S2, dissolving 1.5 g of L-arginine in 100 g of purified water to prepare a catalyst solution;

[0077] S3, after heating the catalyst solution to 65°C, 10 g of silicon powder was added, and after heating to 70°C, the mixture was reacted for 35 hours to obtain a mixed solution of SiO2 sol and silicon powder.

[0078] S4. Filter the mixed solution through a Buchner funnel. The filtrate is the desired silica sol, named SiO2-2#.

[0079] The preparation methods of Examples 3 to 8 and Comparative Examples 1 to 3 are the same as those of Example 1. The specific experimental parameters are shown in Table 1.

[0080] Table 1 Experimental parameters of each embodiment and comparative example

[0081]

[0082] Test method:

[0083] TEM test: The silica sol was diluted to 1 wt.%, and the silica sol sample was placed in an ultrasonic oscillator for dispersion. The morphology and particle size of the SiO2 particles were observed using a JEM-1400Plus transmission electron microscope produced by JEOL Ltd.

[0084] Silica sol stability test: Add 0.74 mL of 45% potassium hydroxide solution to 100 mL of deionized water. Slowly add 125 g of ammonium molybdate while stirring rapidly. Heat the solution to 60°C, then quickly add 400 g of 35% silica sol. After stopping heating and stirring for 5 minutes, continuously measure the silica sol viscosity with a viscometer, recording the time it takes for the viscosity to reach 2 Pa·s. The acceptable stability time is 9 minutes; a longer time indicates better silica sol stability.

[0085] Determination of the solid content of silica sol: Place a clean beaker on a balance with a precision of five decimal places. Record the mass as m1. Return the balance to zero, add a sample of mass m2, and place in a 60°C oven for 24 hours. After the sample is thoroughly dry, remove it and weigh it, recording it as m3. (Data is accurate to 0.0001g). To reduce experimental error, perform two replicates for each experiment. The calculation formula is as follows.

[0086]

[0087] Average Particle Size Test of Silica Sol Particles: There are two methods for measuring the particle size of SiO2 particles in silica sol: TEM measurement and Malvern laser particle size analyzer. TEM measurement uses NanoMeasure software to measure particle diameter based on TEM results. The Malvern laser particle size analyzer is used to determine the overall particle size distribution. For particle size analysis, the solution is typically diluted to a 1% concentration at 25°C and then sonicated for 5 minutes to fully disperse the particles. Three tests are performed per run. Zeta potential testing involves diluting a series of samples to different concentrations. Three tests are then performed at each concentration using a laser particle size analyzer, and the average value is calculated.

[0088] XRD test: X-ray diffraction (XRD) pattern was run at 40 kV and 50 mA, Cu Kα radiation Used to characterize the crystal structure of the material, the scanning temperature is set to 25 ° C and the scanning speed is 5 ° min -1 The test angle is 5 to 80°, and information such as the composition and atomic structure of the material can be obtained.

[0089] Metal ion content test method: determined by atomic absorption spectrometry.

[0090] Figure 1 This is the XRD spectrum of SiO2-6#. It can be seen from the figure that the diffraction peak of the prepared silica sol sample is highly consistent with the SiO2 standard card PDF#50-0511, and there are no other impurities, which proves that the sample is of high purity.

[0091] Table 2 Properties of silica sols in various embodiments and comparative examples

[0092] name <![CDATA[SiO2 content]]> Silicon powder conversion rate% Metal ion concentration Particle size Example 1 <![CDATA[SiO2-1#]]> 15.69％ 91.5％ ≤50ppm 30.24±3.21 Example 2 <![CDATA[SiO2-2#]]> 20.31％ 94.8％ ≤50ppm 27.68±2.87 Example 3 <![CDATA[SiO2-3#]]> 24.04％ 93.5％ ≤50ppm 25.35±2.21 Example 4 <![CDATA[SiO2-4#]]> 25.29％ 90.8％ ≤50ppm 8.21±2.14 Example 5 <![CDATA[SiO2-5#]]> 26.35％ 94.6％ ≤50ppm 18.34±2.62 Example 6 <![CDATA[SiO2-6#]]> 26.66％ 95.7％ ≤50ppm 27.45±2.21 Example 7 <![CDATA[SiO2-7#]]> 26.83％ 96.3％ ≤50ppm 22.68±3.18 Example 8 <![CDATA[SiO2-8#]]> 26.41％ 94.8％ ≤50ppm 15.79±2.53 Comparative Example 1 <![CDATA[SiO2-a#]]> 23.46％ 84.2％ ≤50ppm 18.68±10.21 Comparative Example 2 <![CDATA[SiO2-b#]]> 17.75％ 63.7％ ≤50ppm 24.16±3.43 Comparative Example 3 <![CDATA[SiO2-c#]]> 21.31％ 76.5％ ≤50ppm 27.36±3.92

[0093] Table 2 lists the properties of the silica sols prepared in each example and comparative example. Particle size was measured using a Malvern laser particle size analyzer. As can be seen from the table, the SiO2 particles in the silica sols of each example exhibit good monodispersity, high silicon powder conversion rates, and metal ion contents ≤50 ppm. This demonstrates that the silica sol preparation method of the present invention can produce high-purity, highly monodisperse silica sols.

[0094] Figure 4 (a) Transmission electron microscopy characterization of SiO2-a#, (b) Malvern laser particle size distribution diagram of SiO2-a#; it can be seen from the figure that when ammonia water is used as a catalyst, the particle size distribution of SiO2 particles in the prepared silica sol is large and the monodispersity is poor.

[0095] The silica sol of Example 6 was concentrated using a rotary evaporator to increase the solid content to 35.5%. The concentrated silica sol still had good stability and did not settle when stored at room temperature for 6 months.

[0096] The silica sol SiO2-6# prepared in Example 6 was compared with two commercially available products, and their particle size distribution and Zeta potential were tested.

[0097] Their morphology and particle size test results are shown in Figure 2 and Figure 3 .

[0098] The JN-40 SiO2 sol produced by Fuzhou Sanbang Silicon Material Co., Ltd. has a solid content of 40% and a metal ion content of up to 0.3%. Figure 2 (c) and Figure 3 (c) It can be seen that its particle size distribution is between 3nm-17nm, Figure 3 The four peaks in (c) indicate a wide particle size distribution, with an average particle size of 11.21 nm and a Zeta potential of -11.21 mV, indicating that the SiO2 sol has poor stability. When encountering a high-salt mixture, it will cause rapid flocculation and failure. Its selling price is 7,000 yuan / ton.

[0099] The AS-40 SiO2 sol produced by Grace Company of the United States has a solid content of 40%. Figure 3 (b) The three experimental curves are similar, with a particle size distribution between 12 nm and 38 nm, an average particle size of 22.79 nm, and a zeta potential of -51.7 mV. The selling price is 40,000 yuan / ton.

[0100] The SiO2-6# sol has a solid content of 26.66%, a metal ion content of ≤50ppm, and an average particle size of 27.69nm, which is similar to the particle size distribution results obtained under transmission electron microscopy. Its zeta potential is -43.9mV, indicating that the silica sol has good stability.

[0101] In the examples, silicon powder was purchased from the 1688 website. 200-mesh 99% silicon powder costs 15,000 yuan / ton, and L-arginine costs 50,000 yuan / ton. Based on the conversion rate of Example 6, a silica sol with a solid content of 26.66% was prepared at a raw material cost of only 2,550 yuan / ton. Converted to a 40% solid content, the raw material cost is 3,826 yuan / ton. Furthermore, the method of the present invention has low energy consumption, does not use organic solvents, generates no wastewater, and has low production costs. Therefore, the silica sol prepared by the present invention can generate significant economic benefits.

[0102] According to the stability test method used in the patent "A Silica Sol for Synthesizing Acrylonitrile Catalyst and Its Preparation Method", application number 201910918104.3, the stability of three silica sols was tested. After experimental testing, it was found that the time for the viscosity of SiO2-6#, AS-40 type, and JN-40 type SiO2 sols to reach 2Pa·S was 12 minutes and 40 seconds, 14 minutes and 01 seconds, and 2 minutes and 27 seconds, respectively. This shows that the stability of SiO2-6# sol is similar to that of AS-40 type SiO2 sol, and much better than that of JN-40 type SiO2 sol.

[0103] In Examples 9 to 12, the silica sol prepared in Example 6 was used to prepare carbon-coated silica particles.

[0104] The spray dryer used in the examples is the HF-800BY model produced by Shanghai Hefan Instrument Co., Ltd.

[0105] Example 9

[0106] The method for preparing carbon-coated silica particles comprises the following steps:

[0107] S1, add purified water to adjust the solid content of silica sol to 20%;

[0108] S2, weigh 20 g of the silica sol prepared in S1, add 4.75 g of α-lactose, add 220 g of deionized water, and stir for 3 h to prepare solution A;

[0109] S3, spray drying the solution A prepared in step S2 to collect the powder. The spray drying parameters are: inlet temperature: 180°C; air flow rate: 70%; peristaltic pump injection rate: 20%; outlet temperature: 200°C.

[0110] S4, calcining the powder in step S3 in a nitrogen atmosphere, calcining conditions: 1100 ° C, 6 h, heating rate 5 ° C min -1 .

[0111] The prepared carbon-coated silica particles were named M-SiO2@C-30.

[0112] Example 10

[0113] Only the amount of α-lactose in Example 9 was changed to 2.7 g, and the prepared carbon-coated silica particles were named M-SiO2@C-20.

[0114] Example 11

[0115] Only the amount of α-lactose in Example 9 was changed to 1.2 g, and the prepared carbon-coated silica particles were named M-SiO2@C-10.

[0116] Comparative Example 4

[0117] The method for preparing silicon dioxide particles not coated with carbon comprises the following steps:

[0118] S1, add purified water to adjust the solid content of silica sol to 20%;

[0119] S2, weigh 20 g of the silica sol prepared in S1, add 220 g of deionized water, and stir for 3 h to prepare solution A;

[0120] S3, spray drying the solution A prepared in step S2 to collect the powder. The spray drying parameters are: inlet temperature: 180°C; air flow rate: 70%; peristaltic pump injection rate: 20%; outlet temperature: 200°C.

[0121] S4, calcining the powder in step S3 in a nitrogen atmosphere, calcining conditions: 1100 ° C, 6 h, heating rate 5 ° C min -1 .

[0122] The prepared carbon-coated silica particles were named M-SiO2@C-0.

[0123] Test method:

[0124] Scanning electron microscopy (SEM) was used to characterize the surface morphology and structure of the materials. The operating voltage of transmission electron microscopy (TEM) was 200 kV.

[0125] XRD test: X-ray diffraction (XRD) pattern was run at 40 kV and 50 mA, Cu Kα radiation Used to characterize the crystal structure of the material, the scanning temperature is set to 25 ° C and the scanning speed is 5 ° min -1 , the test angle is 5~80°.

[0126] Raman spectroscopy at wavenumbers 400-2000 cm -1 X-ray photoelectron spectroscopy (XPS) was performed with a monochromatic Al Kα X-ray source.

[0127] Thermogravimetric analyzer (TG) dynamic weighing range: ±100 mg, weighing accuracy: ±0.1%, weighing precision: ±0.01%.

[0128] The battery working electrode is prepared by mixing a SiO2-based active material, carbon black (SuperP), carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) in a mass ratio of 8:1:0.5:0.5. A certain amount of CMC and SBR are first weighed into a cryovial, then the fully ground active material and SuperP are added, and finally ball mill beads are added and thoroughly mixed in a homogenizer. The resulting slurry is spread on copper foil and then flattened with an applicator to a coating thickness of 75 μm. It is then vacuum-dried at 80°C overnight. The areal loading of the active material is approximately 0.8 mg cm -2 . The CR2032 half-cell was assembled in an argon-filled glove box, using metallic lithium as the electrode and reference electrode, polypropylene film (Celgard 2000) as the separator, 1M LiPF6 in ethylene carbonate (EC) / diethyl carbonate (DEC) / dimethyl carbonate (DMC) (volume ratio of 1:1:1) solution and 10 wt.% fluoroethylene carbonate (FEC) solution as the electrolyte. Constant current charge-discharge test, rate performance test and long cycle performance test were carried out on the Blue Electric test system. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) measurements were carried out on the Autolab PGSTAT 302N electrochemical workstation. The charge-discharge and CV curves were obtained at 0~3V (vs.Li + / Li), and the EIS was measured between 0.1 Hz and 100 Hz with an amplitude of 10 mV.

[0129] Figure 5 (a) XRD spectra and (b) Raman spectra of M-SiO2@C-0, M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30. As can be seen from the figure, the diffraction peaks of the samples are highly consistent with those of the pure SiO2 standard card PDF#76-1390, and no characteristic peaks corresponding to Si are found, which proves that the purity of the samples is high and SiO2 is not reduced to silicon element during the high-temperature calcination process.

[0130] Figure 6 These are the TG curves of M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30. The reason for the weight loss is the combustion and decomposition of carbon. As can be seen from the figure, the carbon content of M-SiO2@C-10 is about 11%, the carbon content of M-SiO2@C-20 is about 18%, and the carbon content of M-SiO2@C-30 is about 28%.

[0131] Figure 7 (a) XPS full spectrum of M-SiO2@C-0 and M-SiO2@C-10; (b) XPS silicon spectrum, (c) carbon spectrum and (d) oxygen spectrum of M-SiO2@C-10; Figure 7As can be seen in (a), the peak at 284.8 eV corresponds to C1s in the material, while the peak at 153 eV corresponds to Si2p in the material. Compared to M-SiO2@C-0, which only has characteristic peaks of O1s and Si2p, M-SiO2@C-10 contains characteristic peaks of O1s, C1s, and Si2p, indicating that carbon has been successfully coated on the surface of the M-SiO2@C-10 sample. Figure 7 (c) is the carbon spectrum of M-SiO2@C-10 material, the peak at 289.1eV corresponds to C=O bond, the peak at 286.5eV corresponds to CO bond, and the peak at 284.8eV corresponds to C=C bond; Figure 7 (d) is the oxygen spectrum of the M-SiO2@C-10 material. 532.8 eV corresponds to the C=O bond and 533.3 eV corresponds to the Si-O bond, indicating that silicon element exists in the material in the form of SiO2.

[0132] Figure 8 (a)(b)(c) are SEM photos of M-SiO2@C-0 at different magnifications. It can be seen from the figure that the particle morphology is uniform, and the diameter is concentrated in the range of 1 to 10 μm. After high magnification, it can be clearly seen that the particles are secondary spherical particles formed by the agglomeration of many monodisperse SiO2 primary particles.

[0133] from Figure 9 It can be seen from the TEM images that the TEM images of the unbroken M-SiO2@C-10 are as follows Figure 9 As shown in (a), it shows a solid structure with a particle diameter of about 2μm. At the same time, the corresponding element distribution is as follows Figure 10 As shown in (d)-(f), the elements C, O, and Si are evenly distributed on the surface of the material. Figure 10 (g) Optical photograph of ~2000g of M-SiO2@C-10 prepared using spray drying technology. This technology can achieve large-scale preparation of this material, laying the foundation for mass production.

[0134] from Figure 11 It can be seen that at a scan rate of 0.1 mV-1 from 0.01 to 3 V, reduction peaks were observed at 0.5-0.75 V and 1.5 V for M-SiO2@C-10, M-SiO2@C-20 and M-SiO2@C-30, and two oxidation peaks were observed at 0.3 V and 1.08 V.

[0135] from Figure 12 It can be seen that in the first cycle 20mA g -1At a current density of 1.5 GHz, M-SiO2@C-0, M-SiO2@C-10, M-SiO2@C-20, and M-SiO2@C-30 can provide first-cycle discharge capacity / charge capacity of 100 / 44, 1198 / 744, 498 / 492, and 256 / 87 mAh g, respectively. -1 At 50mAg -1 After 100 cycles at a current density of 100, the discharge capacity / charge capacity provided by the battery are 40 / 39, 559 / 553, 498 / 492, and 341 / 339 mAh g -1 capacity.

[0136] from Figure 13 It can be seen that with the increase of current density, the reversible capacity gradually decreases and returns to the initial 1Ag -1 When the capacity is kept at the initial level, the good rate performance is related to the material coating structure and the size of the primary particles. -1 The capacities available at current densities of 662, 629, 568, 482, and 448 mAh g -1 ; M-SiO2@C-20 at 0.1, 0.2, 0.4, 0.8, 1Ag -1 The capacities available at current densities of 458, 327, 253, 165, and 111 mAh g -1 ; M-SiO2@C-30 at 0.1, 0.2, 0.4, 0.8, 1Ag -1 The capacities available at current densities of 334, 158, 125, 102, and 21 mAh g -1 .

[0137] from Figure 14 It can be seen that the capacity of the carbon-free sample M-SiO2@C-0 gradually increases from 32 mAh g to 100 mAh g with the increase of cycle number at 1C. -1 Up to 54mAh g -1 This is because as the number of cycles increases, there are more active sites inside the material to promote the insertion and extraction of lithium ions, and there are more defects to store lithium ions, but its capacity remains in a low range; the M-SiO2@C-10 sample still has 281mAh g after 1000 cycles at 1C. -1 The retention capacity of the M-SiO2@C-20 sample increased from the initial 341 mAh g to 1000 mAh g after 1000 cycles at the same current density. The coulombic efficiency increased to 95% after 20 cycles and remained above 99% after 45 cycles, indicating that the material has excellent cycle stability.-1 Reduced to 214mAh g -1 The capacity retention rate is 62%, which is slightly higher than that of M-SiO2@C-10. Under the same experimental conditions, the capacity of M-SiO2@C-30 increases from 210 mAh g to 1000 mAh g after 1000 cycles. -1 Reduced to 162mAh g -1 , the capacity retention rate is 77%.

[0138] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing high-purity silica sol, characterized in that: The following steps are involved: S1, activating silicon powder to obtain activated silicon powder; S2, dissolving a basic amino acid in water to prepare a catalyst solution, wherein the basic amino acid is a combination of one or more of arginine, lysine, or histidine; S3, adding the activated silicon powder to the catalyst solution under heating conditions, and hydrolyzing the solution to obtain a mixture of silicon powder and nano-silicon dioxide; S4, filtering the mixed solution of silicon powder and nano-silicon dioxide, and the filtrate is high-purity silica sol; The weight ratio of water, silicon powder and basic amino acid is 100:(8-13):(0.2-2); In step S3, the reaction temperature is 65° C.-90° C., and the reaction time is 15 h-48 h.

2. The method for preparing high-purity silica sol according to claim 1, wherein The basic amino acid is L-arginine.

3. The method for preparing high-purity silica sol according to claim 1, wherein The silicon powder is 100-200 mesh, and the purity is not less than 99.0%.

4. A silica sol prepared by the method for preparing high-purity silica sol according to any one of claims 1 to 3, characterized in that: The silica sol has a particle size of 8nm-30nm, a solid content of (10-30) wt%, and a metal ion content of less than 50ppm.

5. A method for preparing carbon-coated silica particles prepared from the high-purity silica sol according to claim 4, characterized in that: The following steps are involved: The first step is to add sugar to the silica sol in proportion to prepare a silica sugar solution, wherein the sugar is α-lactose, and the mass ratio of the silica to α-lactose is 1:1.2-1:4.75; The second step is spray drying the silicon dioxide sugar solution to form a powder; The third step is to calcine the powder to obtain silicon dioxide coated with a carbon layer. The calcination conditions are: in a nitrogen atmosphere, a heating rate of 5°C min -1 , calcined at 1100℃ for 6h. 6 . Carbon-coated silica particles prepared by the method for preparing carbon-coated silica particles according to claim 5 . 7 . A negative electrode material comprising the carbon-coated silica particles according to claim 6 .

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