Preparation method and application of organic-inorganic double-layer coated silicon-based composite negative electrode material

Abstract

The invention provides a preparation method and application of an organic-inorganic double-layer coated silicon-based composite negative electrode material, and belongs to the field of lithium ion battery negative electrode materials, and the preparation method comprises the following steps: carrying out ball milling on an industrial wire cutting silicon wafer excess material, and sieving to obtain nano silicon powder; preparing a precursor solution containing nano silicon powder, hexadecyl trimethyl ammonium bromide, beta-lactose, boric acid and graphene oxide; carrying out hydrothermal reaction on the precursor solution to obtain a nano silicon-coated beta-lactose composite material; performing high-temperature carbonization on the nano silicon-coated beta-lactose composite material, and cooling to obtain a silicon-coated carbon composite material; mixing and reacting the silicon-carbon composite material, Tween 80, titanium tetraisopropoxide and a hydrochloric acid solution to obtain the nano silicon-carbon-titanium dioxide composite material. The material shows relatively high capacity retention ratio and excellent cycling stability, the reversible specific capacity reaches up to 898 mAh / g after 200 cycles, and the capacity retention ratio is 80%.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery anode materials, specifically relating to a method for preparing and applying an organic-inorganic double-layer coated silicon-based composite anode material. Background Technology

[0002] As an advanced energy storage technology, lithium-ion batteries (LIBs) are now widely used in all aspects of daily life. However, in order to popularize the rapid growth of electric vehicles and intelligent robots, developing electrode materials with high energy density, excellent stability, and high safety is currently a top priority.

[0003] Alloy anodes (Sn, Ge, Si, etc.) offer higher energy densities compared to graphite electrodes currently used in lithium-ion batteries. In particular, silicon (Si) is considered the most attractive anode for lithium-ion batteries due to its abundant natural resources in the Earth's crust, low redox voltage, and high specific capacity (~3700 mAh g⁻¹). -1 And environmental friendliness. Unfortunately, due to the fact that in Li x The migration at the interface between Si and the Si phase causes a sharp increase in stress on the outer surface of Si particles. Si undergoes significant volume changes (>300%) during the lithiation / delithiation process, leading to structural breakage and electrode material separation, resulting in an unstable SEI film and short battery life. Furthermore, the low electronic conductivity significantly hinders the reaction kinetics of the lithium-ion electrode, limiting the rapid transport of lithium ions.

[0004] The key to solving the above problems is to develop high-performance silicon-carbon anode materials, which requires improvements to existing silicon-carbon anode materials. Summary of the Invention

[0005] The purpose of this invention is to propose a method for preparing and applying an organic-inorganic double-layer coated silicon-based composite anode material. This invention uses low-cost industrial wire-cut silicon wafer scrap as the silicon source, and prepares nano-silicon by high-energy ball milling of the scrap. Then, the nano-silicon is first coated using β-lactose as a carbon source via a hydrothermal method, followed by high-temperature carbonization to obtain a silicon@carbon composite material. Finally, the silicon@carbon material is secondly coated using a sol-gel method with titanium tetraisopropoxide as the titanium source, ultimately obtaining a silicon@carbon@titanium dioxide lithium-ion battery anode material.

[0006] In the silicon@carbon@titanium dioxide composite material prepared by this method, nano-silicon is encapsulated within amorphous carbon spheres, achieving a coated silicon-carbon anode. This structure avoids contact between the nano-silicon and the electrolyte and buffers the volume expansion during the lithiation / delithiation process of the nano-silicon. The amorphous TiO2 layer exhibits strain-relaxed elastic behavior, thereby maintaining the integrity of the anode and stabilizing the volume expansion during lithium insertion and deintercalation. Furthermore, due to the absence of long-range order and the presence of defects, the amorphous TiO2 layer can provide a high lithium-ion diffusion rate, thus increasing the potential for lithium deposition. + The prepared silicon-based anode material exhibits high capacity retention and excellent cycle stability, and is considered an ideal anode material for lithium-ion batteries.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing an organic-inorganic bilayer coated silicon-based composite anode material includes the following steps:

[0009] Step 1: Preparation of nano-silicon: Ball milling and sieving of industrial wire-cut silicon wafer residue to obtain nano-silicon powder;

[0010] Step 2: Prepare the precursor solution: Disperse the nano-silicon powder and hexadecyltrimethylammonium bromide obtained in Step 1 into deionized water to obtain solution A; disperse β-lactose, boric acid and graphene oxide into deionized water to obtain solution B; then mix solution A and solution B and disperse them to obtain the precursor solution.

[0011] Step 3: Preparation of nano-silicon@β-lactose composite material: The precursor solution obtained in Step 2 is subjected to hydrothermal reaction. After the reaction is completed, the mixture is centrifuged, washed and dried in sequence to obtain nano-silicon@β-lactose composite material.

[0012] Step 4: Preparation of nano-silicon@carbon composite material: The nano-silicon@β-lactose composite material obtained in Step 3 is subjected to high-temperature carbonization, and after cooling, silicon@carbon composite material is obtained, denoted as Si@C;

[0013] Step 5: Preparation of nano-silicon@carbon@titanium dioxide composite material: The Si@C composite material from Step 4 and Tween 80 are dispersed in deionized water to obtain solution C; tetraisopropoxide titanium and hydrochloric acid solution are dispersed in anhydrous ethanol to obtain solution D; solutions C and D are mixed and reacted, and after the reaction is completed, they are centrifuged, washed and dried in sequence to obtain nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

[0014] Further, in step one, zirconia grinding balls with diameters of 5, 8, 10, and 15 mm are selected, and their corresponding mass ratio is 2:2:2:1. The industrial wire-cut silicon wafer scrap is placed in equal portions into two or four 1000ml zirconia grinding jars. The mass ratio of grinding balls to industrial wire-cut silicon wafer scrap is 50:1. The grinding mill speed is 400-700 r / min, and the grinding time is 10-18 hours, preferably 12 hours. At least one-third of the space in the zirconia jars must be reserved.

[0015] Furthermore, in step two, the conditions for dispersing nano-silicon powder and hexadecyltrimethylammonium bromide in deionized water are as follows: first, ultrasonic dispersion for 0.5-1 h, followed by magnetic stirring for 2-3 h, to obtain solution A; the conditions for dispersing β-lactose, boric acid, and graphene oxide in deionized water are as follows: magnetic stirring at 40-60℃ for 3-5 h, to obtain solution B; the conditions for dispersing solution A and solution B after mixing are as follows: solution A is slowly introduced into solution B while it is being stirred, and magnetic stirring is continued for 2 h, to obtain the precursor solution.

[0016] Furthermore, in step two, the content of nano-silicon in solution A is 0.5-1g, the content of hexadecyltrimethylammonium bromide in solution A is 2-5mmol; the content of β-lactose in solution B is 5-10g, the mass percentage of boric acid in solution B is 5%-10%; and the mass percentage of graphene oxide in solution B is 5-10%.

[0017] Further, the hydrothermal reaction temperature in step three is 180-220℃, and the reaction time is 8-12h. To ensure a more uniform coating of β-lactose on the nano-silicon, the hydrothermal reaction is carried out in a homogeneous reactor at a rotation speed of 20-35 r / min. After the hydrothermal reaction is complete, the dispersion is removed, centrifuged at 8000-1100 r / min for 10-15 min, then washed 2-3 times with ethanol and deionized water, and vacuum dried at 60℃ for 24 h to obtain the nano-silicon@β-lactose composite material.

[0018] Furthermore, the high-temperature carbonization method described in step four is a segmented heating process, which includes first heating to 300-400℃ at a heating rate of 2-3℃ / min for pre-carbonization, holding for 0.5-1h, and then heating to 900-1100℃ at a heating rate of 3-5℃ / min for carbonization, holding for 2-3h, with a nitrogen flow rate of 50-100sccm, so that the carbonization reaction is completely completed.

[0019] Further, in step five, the conditions for dispersing the Si@C composite material and Tween 80 in deionized water are: sonication for 0.5-1 h to obtain solution C; the conditions for dispersing tetraisopropoxide titanium and hydrochloric acid solution in anhydrous ethanol are: magnetic stirring at 50-60℃ for 1-3 h to obtain solution D; the conditions for mixing and reacting solutions C and D are: slowly adding solution C to the stirring solution D, and continuing magnetic stirring for 4-6 h. After the reaction is complete, the mixed liquid is removed, centrifuged at 8000-1100 r / min for 10-15 min, then washed 3-5 times with anhydrous ethanol, and vacuum dried at 60℃ for 24 h to obtain nano-silicon@carbon@titanium dioxide composite material.

[0020] Furthermore, in step five, the content of Si@C composite material in solution C is 0.5-1g; the mass percentage of Tween 80 in solution C is 5-10%; the content of tetraisopropoxide titanium in solution D is 750-1500µl; and the concentration of hydrochloric acid in solution D is 4M.

[0021] The key technical points in the preparation process of the nano-silicon@carbon@titanium dioxide composite anode material of this invention are: the mass ratio of nano-silicon to β-lactose, the time and temperature of the hydrothermal reaction, the appropriate annealing temperature and holding time, the amount of tetraisopropoxide titanium, and the appropriate concentration of hydrochloric acid solution.

[0022] The mass ratio of nano-silicon to β-lactose is 1:5-1:10, the hydrothermal reaction temperature is 180-220℃, and the hydrothermal reaction time is 8-12h. The segmented heating temperatures are: first, holding at 300-400℃ for 0.5-1h, then holding at 900-1100℃ for 2-3h. The amount of tetraisopropoxide titanium used is 750-1500µl, and the concentration of hydrochloric acid is 4M. Within this parameter range, nano-silicon can be coated inside the carbon spheres, and an amorphous titanium dioxide layer of suitable thickness can be formed on the outer layer of the carbon spheres.

[0023] In one embodiment of the present invention, the preparation method of the organic-inorganic bilayer coated silicon-based composite anode material includes the following steps:

[0024] Step 1: Preparation of Nano-Silicon: Equal portions of industrial wire-cut silicon wafer scrap are placed into two or four 1000ml zirconia ball mill jars, with a ball milling ball to polycrystalline silicon cutting sludge mass ratio of 50:1. The zirconia ball mill jars are then placed on a planetary ball mill. The diameters of the zirconia ball milling balls are 5, 8, 10, and 15 mm, with a corresponding mass ratio of 2:2:2:1. The ball mill is operated at 400-700 r / min at room temperature for dry milling for 10-18 hours. At least one-third of the space in the zirconia jars must be reserved. The milled silicon powder is then sieved to obtain nano-silicon powder.

[0025] Step 2: Prepare the precursor solution: Disperse 0.5-1g of nano-silicon powder and 2-5mmol of hexadecyltrimethylammonium bromide in deionized water, sonicate for 0.5-1h, and magnetically stir for 2-3h to obtain solution A; disperse 5-10g of β-lactose, 5-10% boric acid, and 5-10% graphene oxide in an appropriate amount of deionized water, and magnetically stir at 40-60℃ for 3-5h to obtain solution B; then slowly introduce solution A into solution B while it is being stirred, and continue magnetically stirring for 2h to obtain the precursor solution.

[0026] Step 3: Preparation of nano-silicon@β-lactose composite material: The precursor solution prepared in Step 2 above was placed in a 100ml high-temperature resistant reactor. The reactor was then placed in a homogeneous reactor for a high-temperature hydrothermal reaction. The hydrothermal reaction temperature was 180-220℃, the reactor rotation speed was 20-35 r / min, and the reaction time was 8-12 h. After the reaction was complete, the dispersion was centrifuged at 8000-1100 r / min for 10-15 min, then washed 2-3 times with ethanol and deionized water, and vacuum dried at 60℃ for 24 h to obtain the nano-silicon@β-lactose composite material.

[0027] Step 4: Preparation of nano-silicon@carbon composite material: After grinding the dried nano-silicon@β-lactose composite material, place it in a quartz boat and heat it to 300-400℃ at a heating rate of 2-3℃ / min under a nitrogen atmosphere with a gas flow rate of 50-100 sccm, holding for 0.5-1h. Then heat it to 900-1100℃ at a heating rate of 3-5℃ / min, holding for 2-3h to obtain the Si@C composite material.

[0028] Step 5: Preparation of nano-silicon@carbon@titanium dioxide composite material: Disperse 0.5-1g of the Si@C composite material from Step 4 in deionized water, add 5-10% Tween 80, and sonicate for 0.5-1h to obtain solution C; disperse 750-1500µl of tetraisopropoxide titanium and 4M hydrochloric acid solution in anhydrous ethanol, and magnetically stir at 50-60℃ for 1-3h to obtain solution D; slowly add solution C to the stirring solution D, and continue magnetic stirring for 4-6h. After the reaction is complete, remove the mixed liquid and centrifuge at 8000-1100r / min for 10-15min, then wash 3-5 times with anhydrous ethanol, and vacuum dry at 60℃ for 24h to obtain nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

[0029] This invention also provides the aforementioned organic-inorganic bilayer coated silicon-based composite anode material, which consists of an innermost layer of nano-silicon, a middle layer of silicon-coated amorphous carbon, and an outermost layer of amorphous titanium dioxide. The nano-silicon is coated inside the amorphous carbon spheres, achieving a coated silicon-carbon anode structure. This structure avoids contact between the nano-silicon and the electrolyte and buffers the volume expansion during the lithiation / delithiation process of the nano-silicon. The amorphous titanium dioxide layer exhibits strain-relaxed elastic behavior, compensating for the insufficient mechanical strength of the carbon layer, thereby maintaining anode integrity and stabilizing the volume expansion during lithium insertion and deintercalation. Furthermore, due to the lack of long-range order and the presence of defects, the amorphous titanium dioxide layer can provide a high lithium-ion diffusion rate, thereby increasing the lithium ion diffusion capacity. + Electrochemical reactivity.

[0030] This invention also provides the application of the aforementioned organic-inorganic bilayer coated silicon-based composite anode material in lithium-ion batteries. The silicon-based composite anode material exhibits high capacity retention and excellent cycle stability; after 200 cycles, the reversible specific capacity of this silicon-based anode reaches 898 mAh / g, with a capacity retention of 80%.

[0031] The present invention has the following beneficial effects:

[0032] (1) The present invention uses industrial silicon wafer scrap as silicon source and reduces silicon particle size by high-energy ball milling. It has the advantages of low cost, simple operation, environmental friendliness and large-scale industrial production.

[0033] (2) A silicon-carbon anode with a coated structure was achieved by using a hydrothermal synthesis process to encapsulate nano-silicon inside amorphous carbon spheres formed by β-lactose. This structure can avoid contact between nano-silicon and electrolyte and buffer the volume expansion during the lithiation / delithiation process of nano-silicon; the graphene oxide in the carbonization process is reduced, and a three-dimensional conductive network is pre-constructed in the carbon layer to provide a channel for electron transport.

[0034] (3) The titanium dioxide layer is fabricated via the sol-gel method, which is simple and environmentally friendly. The amorphous TiO2 layer exhibits strain-relaxed elastic behavior, thus maintaining the integrity of the anode and stabilizing the volume expansion during lithium insertion and extraction, thereby improving the cycle stability of the lithium-ion battery. On the other hand, due to the absence of long-range order and the presence of defects, the amorphous TiO2 layer can provide a high lithium-ion diffusion rate, thereby increasing the lithium-ion diffusion rate. + Electrochemical reactivity. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 This is a flowchart illustrating the preparation process of the silicon@carbon@titanium dioxide composite anode material of the present invention.

[0037] Figure 2 (a) The silicon@carbon@titanium dioxide anode of Example 1 at 0.1 mV s -1 The following cyclic voltammetry chart, Figure 2 (b) is a constant current charge-discharge curve of the silicon@carbon@titanium dioxide anode of Example 1 at 0.05C.

[0038] Figure 3 The XRD curves are for the SiNPs, Si@C, and Si@C@TiO2 composite materials of Example 1.

[0039] Figure 4 The graph shows the cycling stability of the silicon@carbon@titanium dioxide anode of Example 1 for the first 200 cycles at 0.2 C. Detailed Implementation

[0040] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0041] Comparative Example

[0042] Step 1: Preparation of nano-silicon: Equal portions of industrial wire-cut silicon wafer scrap are placed into two or four 1000ml zirconia ball mill jars. The ratio of grinding beads to polycrystalline silicon cutting sludge is 50:1. The zirconia ball mill jars are then placed on a planetary ball mill. The diameters of the zirconia grinding beads are 5, 8, 10, and 15 mm, with a corresponding mass ratio of 2:2:2:1. The ratio of grinding beads to industrial wire-cut silicon scrap is 50:1. Dry ball milling is performed at room temperature and a rotation speed of 400-700 r / min for 10-18 hours. At least one-third of the space in the zirconia jars must be reserved. The milled silicon powder is then sieved to obtain nano-silicon powder.

[0043] Step 2: Prepare the precursor solution: Disperse 0.5g of nano-silicon powder and 2mmol of cetyltrimethylammonium bromide in deionized water, sonicate for 0.5h, and magnetically stir for 2h to obtain solution A; disperse 5% boric acid and 5% graphene oxide in an appropriate amount of deionized water, and magnetically stir at 40-60℃ for 3h to obtain solution B; then slowly introduce solution A into solution B while it is being stirred, and continue magnetic stirring for 2h to prepare the precursor solution.

[0044] Step 3: Place the precursor solution prepared in Step 2 into a 100ml high-temperature resistant reactor. Then, place the reactor into a homogeneous reactor for a high-temperature hydrothermal reaction. The hydrothermal reaction temperature is 180℃, the reactor rotation speed is 20r / min, and the reaction time is 8h. After the reaction is complete, remove the dispersion and centrifuge it at 8000-1100r / min for 10-15min. Then, wash it 2-3 times with ethanol and deionized water, and vacuum dry it at 60℃ for 24h.

[0045] Step 4: After grinding the dried powder material, place it in a quartz boat and heat it to 300℃ at a heating rate of 2-3℃ / min under a nitrogen atmosphere with a gas flow rate of 50-100 sccm. Hold the temperature for 0.5h, then heat it to 900℃ at a heating rate of 3-5℃ / min and hold the temperature for 2h.

[0046] Step 5: Disperse 0.5g of the powdered material from Step 4 in deionized water, add 5% Tween 80, and sonicate for 0.5h to obtain solution C; disperse a 4M hydrochloric acid solution in anhydrous ethanol, and magnetically stir at 50-60℃ for 1h to obtain solution D; slowly add solution C to the stirring solution D, and continue magnetic stirring for 4h. After the reaction is complete, remove the mixed liquid and centrifuge at 8000-1100r / min for 10-15min, then wash 3-5 times with anhydrous ethanol, and vacuum dry at 60℃ for 24h.

[0047] Example 1

[0048] Step 1: Preparation of nano-silicon: Equal portions of industrial wire-cut silicon wafer scrap are placed into two or four 1000ml zirconia ball mill jars. The ratio of milling beads to polycrystalline silicon cutting sludge is 50:1. The zirconia ball mill jars are then placed on a planetary ball mill. The diameters of the zirconia milling beads are 5, 8, 10, and 15 mm, with a corresponding mass ratio of 2:2:2:1. The ratio of milling beads to industrial wire-cut silicon scrap is 50:1. Dry milling is performed at room temperature and a rotation speed of 400-700 r / min for 10-18 hours. At least one-third of the space in the zirconia jars must be reserved. The milled silicon powder is then sieved to obtain nano-silicon powder.

[0049] Step 2: Prepare the precursor solution: Disperse 0.5g of nano-silica powder and 2mmol of cetyltrimethylammonium bromide in deionized water, sonicate for 0.5h, and magnetically stir for 2h to obtain solution A; disperse 5g of β-lactose, 5% boric acid, and 5% graphene oxide in an appropriate amount of deionized water, and magnetically stir at 40-60℃ for 3h to obtain solution B; then slowly introduce solution A into solution B while it is being stirred, and continue magnetically stirring for 2h to prepare the precursor solution.

[0050] Step 3: Preparation of nano-silicon@β-lactose composite material: The precursor solution prepared in Step 2 was placed in a 100ml high-temperature resistant reactor. The reactor was then placed in a homogeneous reactor for a high-temperature hydrothermal reaction at 180℃, with a reactor rotation speed of 20r / min and a reaction time of 8h. After the reaction was complete, the dispersion was centrifuged at 8000-1100r / min for 10-15min, and then washed 2-3 times with ethanol and deionized water to obtain the nano-silicon@β-lactose composite material. The material was then vacuum dried at 60℃ for 24h.

[0051] Step 4: Preparation of nano-silicon@carbon composite material: After grinding the dried nano-silicon@β-lactose composite material, place it in a quartz boat and heat it to 300℃ at a heating rate of 2-3℃ / min under a nitrogen atmosphere with a gas flow rate of 50-100 sccm, and hold it for 0.5 h. Then heat it to 900℃ at a heating rate of 3-5℃ / min and hold it for 2 h.

[0052] Step 5: Preparation of nano-silicon@carbon@titanium dioxide composite material: Disperse 0.5g of the Si@C composite material from Step 4 in deionized water, add 5% Tween 80, and sonicate for 0.5h to obtain solution C; disperse 750ul of tetraisopropoxide titanium and 4M hydrochloric acid solution in anhydrous ethanol, and magnetically stir at 50-60℃ for 1h to obtain solution D; slowly add solution C to the stirring solution D, and continue magnetic stirring for 4h. After the reaction is complete, remove the mixed liquid and centrifuge at 8000-1100r / min for 10-15min, then wash 3-5 times with anhydrous ethanol, and vacuum dry at 60℃ for 24h to obtain nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

[0053] Example 2

[0054] Step 1: Preparation of nano-silicon: Equal portions of industrial wire-cut silicon wafer scrap are placed into two or four 1000ml zirconia ball mill jars. The ratio of milling beads to polycrystalline silicon cutting sludge is 50:1. The zirconia ball mill jars are then placed on a planetary ball mill. The diameters of the zirconia milling beads are 5, 8, 10, and 15 mm, with a corresponding mass ratio of 2:2:2:1. The ratio of milling beads to industrial wire-cut silicon scrap is 50:1. Dry milling is performed at room temperature and a rotation speed of 400-700 r / min for 10-18 hours. At least one-third of the space in the zirconia jars must be reserved. The milled silicon powder is then sieved to obtain nano-silicon powder.

[0055] Step 2: Preparation of precursor solution: Disperse 0.75g of nano-silica powder and 3.5mmol of cetyltrimethylammonium bromide in deionized water, sonicate for 0.8h, and magnetically stir for 2.5h to obtain solution A; disperse 7.5g of β-lactose, 7.5% boric acid, and 7.5% graphene oxide in an appropriate amount of deionized water, and magnetically stir at 40-60℃ for 4h to obtain solution B; then slowly introduce solution A into solution B while it is being stirred, and continue magnetically stirring for 2h to prepare the precursor solution.

[0056] Step 3: Preparation of nano-silicon@β-lactose composite material: The precursor solution prepared in Step 2 was placed in a 100ml high-temperature resistant reactor. The reactor was then placed in a homogeneous reactor for a high-temperature hydrothermal reaction at 200℃, with a reactor rotation speed of 25r / min and a reaction time of 10h. After the reaction was complete, the dispersion was centrifuged at 8000-1100r / min for 10-15min, and then washed 2-3 times with ethanol and deionized water to obtain the nano-silicon@β-lactose composite material. The material was then vacuum dried at 60℃ for 24h.

[0057] Step 4: Preparation of nano-silicon@carbon composite material: After grinding the dried nano-silicon@β-lactose composite material, place it in a quartz boat and heat it to 350℃ at a heating rate of 2-3℃ / min under a nitrogen atmosphere with a gas flow rate of 50-100 sccm, and hold it for 0.8h. Then heat it to 1000℃ at a heating rate of 3-5℃ / min and hold it for 2.5h.

[0058] Step 5: Preparation of nano-silicon@carbon@titanium dioxide composite material: Disperse 0.75g of the Si@C composite material from Step 4 in deionized water, add 7.5% Tween 80, and sonicate for 0.8h to obtain solution C; disperse 1100ul of tetraisopropoxide titanium and 4M hydrochloric acid solution in anhydrous ethanol, and magnetically stir at 50-60℃ for 2h to obtain solution D; slowly add solution C to the stirring solution D, and continue magnetic stirring for 5h. After the reaction is complete, remove the mixed liquid and centrifuge at 8000-1100r / min for 10-15min, then wash 3-5 times with anhydrous ethanol, and vacuum dry at 60℃ for 24h to obtain nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

[0059] Example 3

[0060] Step 1: Preparation of nano-silicon: Equal portions of industrial wire-cut silicon wafer scrap are placed into two or four 1000ml zirconia ball mill jars. The ratio of milling beads to polycrystalline silicon cutting sludge is 50:1. The zirconia ball mill jars are then placed on a planetary ball mill. The diameters of the zirconia milling beads are 5, 8, 10, and 15 mm, with a corresponding mass ratio of 2:2:2:1. The ratio of milling beads to industrial wire-cut silicon scrap is 50:1. Dry milling is performed at room temperature and a rotation speed of 400-700 r / min for 10-18 hours. At least one-third of the space in the zirconia jars must be reserved. The milled silicon powder is then sieved to obtain nano-silicon powder.

[0061] Step 2: Prepare the precursor solution: Disperse 1g of nano-silica powder and 5mmol of cetyltrimethylammonium bromide in deionized water, sonicate for 1h, and magnetically stir for 3h to obtain solution A; disperse 10g of β-lactose, 10% boric acid, and 10% graphene oxide in an appropriate amount of deionized water, and magnetically stir at 40-60℃ for 5h to obtain solution B; then slowly introduce solution A into solution B while it is being stirred, and continue magnetically stirring for 2h to prepare the precursor solution.

[0062] Step 3: Preparation of nano-silicon@β-lactose composite material: The precursor solution prepared in Step 2 was placed in a 100ml high-temperature resistant reactor. The reactor was then placed in a homogeneous reactor for a high-temperature hydrothermal reaction at 220℃, with a reactor rotation speed of 35r / min and a reaction time of 12h. After the reaction was complete, the dispersion was centrifuged at 8000-1100r / min for 10-15min, and then washed 2-3 times with ethanol and deionized water to obtain the nano-silicon@β-lactose composite material. The material was then vacuum dried at 60℃ for 24h.

[0063] Step 4: Preparation of nano-silicon@carbon composite material: After grinding the dried nano-silicon@β-lactose composite material, place it in a quartz boat and heat it to 400℃ at a heating rate of 2-3℃ / min under a nitrogen atmosphere with a gas flow rate of 50-100 sccm, and hold it for 1 hour. Then heat it to 1100℃ at a heating rate of 3-5℃ / min and hold it for 3 hours.

[0064] Step 5: Preparation of silicon nano-silicon@carbon@titanium dioxide composite material: 1g of the Si@C composite material from Step 4 was dispersed in deionized water, 10% Tween 80 was added, and the mixture was sonicated for 1 hour to obtain solution C; 1500ul of tetraisopropoxide titanium and a 4M hydrochloric acid solution were dispersed in anhydrous ethanol and magnetically stirred at 50-60℃ for 3 hours to obtain solution D; solution C was slowly added to the stirring solution D, and magnetic stirring was continued for 6 hours. After the reaction was completed, the mixed liquid was removed and centrifuged at 8000-1100 r / min for 10-15 min, then washed 3-5 times with anhydrous ethanol, and vacuum dried at 60℃ for 24 hours to obtain the silicon nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

[0065] Test conditions: The materials prepared in the comparative examples and embodiments above were used as negative electrode materials, mixed with binder PAA-Li and conductive agent (Super-P) at a mass ratio of 80:10:10, and an appropriate amount of deionized water was added as a solvent to form a slurry. This slurry was coated onto copper foil and then vacuum dried and rolled to prepare a negative electrode sheet. A lithium metal sheet was used as the counter electrode. An electrolyte solution of 1 mol / L LiPF6 three-component mixed solvent was used, prepared at an EC:DMC:EMC ratio of 1:1:1 (v / v). A polypropylene microporous membrane was used as the separator. The CR2032 coin cell was assembled in an inert gas-filled glove box. Charge-discharge tests of the coin cells were conducted on a battery testing system from Shenzhen Xinwei. Constant current charge-discharge was performed at room temperature, with the charge-discharge voltage limited to 0.01-2V.

[0066] The electrochemical performance of the final product Si@C@TiO2 in Example 1 was tested. The discharge specific capacity in the first cycle was 1606.6 mAh / g, the charge specific capacity in the first cycle was 1217.8 mAh / g, and the coulombic efficiency in the first cycle was 75.8%. After 200 cycles, the capacity remained at 898.7 mAh / g.

[0067] Table 1 summarizes the performance parameters of silicon-carbon composite anode materials:

[0068] Table 1

[0069]

[0070] Compared to Example 1, no titanium or carbon source was added during the preparation process of the comparative example. As shown in Table 1, the reversible capacity of Example 1 after 200 cycles is significantly higher than that of the comparative example, indicating that the silicon-based composite anode material of this invention has better cycle stability. Furthermore, Si@C@TiO2 also exhibits a high first-cycle coulombic efficiency of 75.8%, enhancing the advantages of silicon-based anode materials in lithium-ion battery fabrication. Considering its simple preparation process and low-cost raw materials, Si@C@TiO2 demonstrates great application potential as a lithium-ion battery anode material.

[0071] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A method for preparing an organic-inorganic double-coated silicon-based composite negative electrode material, characterized in that, The method comprises the following steps: Step one, preparation of nano-silicon: ball milling of industrial wire cutting silicon wafer scrap, sieving to obtain nano-silicon powder; Step two, preparation of precursor solution: dispersing the nano-silicon powder obtained in step one and cetyltrimethylammonium bromide into deionized water to obtain solution A; dispersing beta-lactose, boric acid and graphene oxide into deionized water to obtain solution B; then mixing and dispersing solution A and solution B to obtain a precursor solution; Step three, preparation of nano-silicon@beta-lactose composite material: carrying out hydrothermal reaction on the precursor solution obtained in step two, and then sequentially carrying out centrifugation, washing and drying to obtain a nano-silicon@beta-lactose composite material; Step four, preparation of nano-silicon@carbon composite material: carrying out high-temperature carbonization on the nano-silicon@beta-lactose composite material obtained in step three, and then cooling to obtain a silicon@carbon composite material, denoted as Si@C; Step five, preparation of nano-silicon@carbon@titanium dioxide composite material: dispersing the Si@C composite material in step four and Tween 80 into deionized water to obtain solution C; dispersing titanium tetraisopropoxide and hydrochloric acid solution into anhydrous ethanol to obtain solution D; mixing and reacting solution C and solution D, and then sequentially carrying out centrifugation, washing and drying to obtain a nano-silicon@carbon@titanium dioxide composite material, denoted as Si@C@TiO2.

2. The method for preparing the organic-inorganic double-layer coated silicon-based composite anode material according to claim 1, characterized in that, In step one, zirconium oxide ball milling beads with diameters of 5, 8, 10 and 15 mm are selected, and the corresponding mass ratio is 2:2:2:1; the industrial wire cutting silicon wafer scrap is equally divided into two or four 1000ml zirconium oxide ball milling tanks, the mass ratio of ball milling beads to industrial wire cutting silicon wafer scrap is 50:1, the rotation speed of the ball mill is 400-700 r / min, and the ball milling time is 10-18h. 3.The method of claim 1, wherein the method further comprises: mixing the silicon-based composite negative electrode material with a solvent to form a slurry; and coating the slurry on a current collector to form the organic-inorganic double-layer coated silicon-based composite negative electrode material. In step two, the conditions for dispersing the nano-silicon powder and cetyltrimethylammonium bromide into deionized water are as follows: first ultrasonic dispersion for 0.5-1h, and then magnetic stirring for 2-3h to obtain solution A; the conditions for dispersing beta-lactose, boric acid and graphene oxide into deionized water are as follows: magnetic stirring at 40-60℃ for 3-5h to obtain solution B; The conditions for dispersing solution A and solution B after mixing are as follows: slowly introducing solution A into stirring solution B, and continuing magnetic stirring for 2h to obtain a precursor solution.

4. The method for preparing the organic-inorganic bilayer coated silicon-based composite anode material according to claim 1, characterized in that, In step two, the content of nano-silicon in solution A is 0.5-1g, the content of cetyltrimethylammonium bromide in solution A is 2-5mmol; the content of beta-lactose in solution B is 5-10g, the mass percentage of boric acid in solution B is 5%-10%, and the mass percentage of graphene oxide in solution B is 5-10%. 5.The method of claim 1, wherein the method further comprises, after the step of mixing the silicon-based composite negative electrode material, a step of coating the silicon-based composite negative electrode material with a polymer layer. In step three, the hydrothermal reaction temperature is 180-220℃, the reaction time is 8-12h; the hydrothermal reaction is carried out in a homogeneous reactor, the rotation speed of the homogeneous reactor is 20-35r / min; after the hydrothermal reaction is completed, the dispersion liquid is taken out, centrifuged at 8000-1100r / min for 10-15min, then washed with ethanol and deionized water for 2-3 times, and vacuum dried at 60℃ for 24h to obtain a nano-silicon@beta-lactose composite material.

6. The method for preparing the organic-inorganic bilayer coated silicon-based composite anode material according to claim 1, characterized in that, The high-temperature carbonization method in step four is a segmented heating method, including first heating to 300-400℃ at a heating rate of 2-3℃ / min, holding for 0.5-1h, then heating to 900-1100℃ at a heating rate of 3-5℃ / min, holding for 2-3h, and the nitrogen flow rate is 50-100sccm.

7. The method for preparing the organic-inorganic bilayer coated silicon-based composite anode material according to claim 1, characterized in that, The conditions for dispersing the Si@C composite material and Tween 80 in deionized water in step five are: ultrasonic for 0.5-1h to obtain solution C; the conditions for dispersing titanium tetraisopropoxide and hydrochloric acid solution in anhydrous ethanol are: magnetic stirring at 50-60℃ for 1-3h to obtain solution D; the conditions for mixing and reacting solution C and solution D are: slowly adding solution C into the stirring solution D, and continuing magnetic stirring for 4-6h. After the reaction is completed, the mixed liquid is taken out, centrifuged at 8000-1100r / min for 10-15min, then washed with anhydrous ethanol for 3-5 times, and vacuum dried at 60℃ for 24h to obtain the nano silicon@carbon@titanium dioxide composite material.

8. The method for preparing the organic-inorganic bilayer coated silicon-based composite anode material according to claim 1, characterized in that, The content of Si@C composite material in solution C in step five is 0.5-1g; the mass percentage of Tween 80 in solution C is 5-10%; the content of titanium tetraisopropoxide in solution D is 750-1500µl; and the concentration of hydrochloric acid in solution D is 4M.

9. The organic-inorganic double-layer coated silicon-based composite anode material prepared by the method of any one of claims 1 to 8.

10. The application of the organic-inorganic double-layer coated silicon-based composite anode material of claim 9 in lithium ion batteries.

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