A preparation method and application of carbon-assisted etching porous silicon carbon

Abstract

The present invention discloses a method for preparing porous silicon by carbon-assisted etching and its application, and relates to the field of battery materials. The method comprises the following steps: (1) cleaning waste photovoltaic silicon wafers by ultrasonic treatment to obtain pretreated silicon wafers; (2) reacting the pretreated silicon wafers in step (1) with carbon source materials to obtain silicon-carbon composite materials; (3) etching the silicon-carbon composite materials in step (2) to obtain a porous silicon-carbon mixture; (4) vacuum filtering and drying the porous silicon-carbon mixture in step (3) to obtain a final product. The porous silicon material prepared by the present invention is applied to negative electrode materials of lithium-ion batteries, exhibiting excellent electrochemical properties, having high specific capacity, good cycle stability and excellent rate performance, and having simple process and low cost.

Description

Technical Field

[0001] The invention relates to the field of battery materials, and in particular to a preparation method of carbon-assisted etching porous silicon and application thereof. Background Art

[0002] As energy storage devices, lithium-ion batteries have the characteristics of low cost, high energy density and power density, and long cycle life. In order to meet the growing demand for high-energy lithium-ion batteries (LIBs), it is crucial to develop anode materials to achieve high capacity. Silicon has a very high theoretical capacity (~3580 mAh g −1 ) and has become one of the most promising anode materials, much higher than commercial graphite (372 mAh g -1 However, the dramatic volume change of about 400% during lithiation / delithiation and its low electronic conductivity (about 10 -3 S m -1 ) can easily lead to severe pulverization, electrical insulation, and electrolyte-related side reactions, resulting in rapid structural degradation.

[0003] In order to solve the volume expansion problem of silicon negative electrode, researchers have developed a variety of strategies, among which preparing silicon materials into porous structures is an effective method. The pores inside porous silicon can buffer the volume change of silicon during lithium insertion / delithiation and improve the structural stability of the electrode. There are many methods for preparing porous silicon, including direct thermal reduction, molten salt thermal reduction, dealloying, template removal, chemical method, electrochemical corrosion, metal-assisted etching, etc. Among these methods, only electrochemical corrosion and metal-assisted etching can directly etch silicon into porous silicon in one step, and the obtained silicon is a stable single-crystalline porous structure. The remaining methods are relatively complicated, and the obtained porous silicon is a porous structure formed by stacking multiple silicon particles, which is in a polycrystalline form and unstable. The particles are prone to relative slippage, causing the porous structure to collapse.

[0004] Compared with electrochemical etching and metal-assisted etching, it is necessary to prepare silicon-based electrodes, apply bias, and etch through electrolyte, which is complicated. Metal-assisted etching often requires the use of nano-level precious metals with high work functions, such as Pt, Au, Ag, etc. Due to its high cost, this method has been studied in electronic printing, chip preparation, micro-nano device preparation, etc., but is less used in batteries.

[0005] At present, metal-assisted etching can directly etch elemental silicon into porous silicon. The preparation process is simpler and easier to control than other methods. Metal-assisted chemical etching (MACE) usually uses precious metals (such as silver, gold, platinum, etc.) as catalysts in the presence of HF and oxidants (such as H 2 O 2) in a mixed solution of 2,4-dihydrogen 2-acid and 2,4-dihydrogen 2-acid. However, the MACE method has some disadvantages: (1) The cost of precious metal catalysts is high, which is not conducive to large-scale production. (2) During the etching process, metal catalysts will introduce dense metal impurities, which will affect the electrochemical properties of silicon and reduce its energy density. (3) The post-processing process of removing metal catalysts is complicated and may damage the porous silicon structure.

[0006] Chinese patent application with publication number CN109755520A discloses a porous silicon-carbon composite material and a preparation method thereof, which requires the use of silicon carbide (pure substance) for preparation, and the performance of the prepared product is poor.

[0007] The Chinese patent application with publication number CN115036216A discloses a silicon carbide nanoporous etching method and etching device. The method requires the use of SiO X Or other substances as templates, the preparation steps are complicated, and the structure of the prepared product is surface-coated carbon, and multiple silicon particles are stacked and mixed, and the structural stability is poor.

[0008] Therefore, it is of great significance to develop a non-metal-assisted etching method that does not require metal catalysts to prepare porous silicon. Summary of the invention

[0009] In view of the above problems existing in the prior art, the purpose of the present invention is to provide a method for preparing porous silicon by carbon-assisted etching, which method does not require the use of precious metal catalysts or even metal catalysts, has a simple process and low cost, and the prepared porous silicon material has excellent electrochemical properties and can be used as a high-performance lithium-ion battery negative electrode material. Another purpose of the present invention is to provide an application of the porous silicon material prepared by the above method as a lithium-ion battery negative electrode material.

[0010] In order to achieve the above object, the present invention adopts the following technical solutions:

[0011] A method for preparing porous silicon by carbon-assisted etching comprises the following steps:

[0012] (1) Cleaning the waste photovoltaic silicon wafers by ultrasonic treatment to obtain pretreated silicon wafers;

[0013] (2) reacting the silicon wafer pretreated in step (1) with a carbon source material so that the carbon particles are evenly dispersed on the surface of the silicon particles to obtain a silicon-carbon composite material;

[0014] (3) etching the silicon-carbon composite material obtained in step (2) to obtain a porous silicon-carbon mixture;

[0015] (4) The two-dimensional porous silicon-carbon mixture of step (3) is vacuum filtered and dried to obtain a final product.

[0016] Furthermore, in step (1), the ultrasonic treatment is as follows: ultrasonically cleaning the waste photovoltaic silicon wafers with 0.2%~0.4%wt HCl solution, acetone, ethanol and deionized water in sequence, with each solvent ultrasonically cleaning for 0.8~1.2h.

[0017] Furthermore, in step (2), the carbon source material is one or more of nano-carbon balls, carbon nanotubes, graphene, and activated carbon. The specific steps of step (2) are: waste silicon and carbon source materials are ball-milled in a mass ratio of 1:0.08-0.12, the ball-milling process is carried out using zirconium dioxide balls and a ball milling jar, the mass ratio of zirconium dioxide balls to materials is 30-50:1, and the ball milling is carried out at 300-500 rpm for 10-15 hours to obtain a silicon-carbon composite material.

[0018] Furthermore, in step (2), the carbon source material is acetylene gas, and the specific steps of step (2) are: immersing the pretreated silicon wafer in a 4-6 mol / L ferric chloride solution for 0.8-1.2 hours, taking it out, drying it, placing it in a tube furnace, introducing argon gas as a protective gas, and heating it to 850-950°C; then introducing acetylene gas as a carbon source, and the reaction time is 20-40 minutes; after the reaction is completed, naturally cooling to room temperature to obtain a silicon wafer modified with acetylene-derived carbon, that is, a silicon-carbon composite material.

[0019] Furthermore, in step (3), the solid-liquid ratio of the silicon-carbon composite material to the organic solvent is g / mL 1:40-50; the organic solvent is ethanol or isopropanol; the stirring and mixing time is 30-40 min, and the stirring and mixing temperature is 20-30°C.

[0020] Furthermore, in step (3), the etching method is to use an etching solution or HF vapor or HF-H 2 O 2 Mixed vapor etching

[0021] Furthermore, in step (3), the etching solution contains hydrofluoric acid.

[0022] Further, in step (3), the etching solution further contains an oxidant, the volume ratio of hydrofluoric acid to the oxidant is 3:0.5-1.5, and the oxidant is H 2 O 2 , HNO 3 , at least one of an oxidizing metal salt, wherein the oxidizing metal salt is AgNO 3 HAuCl 4 KAuCl 4 , H 2 PtCl 6 , PdCl 2 At least one of them.

[0023] Furthermore, in step (3), the etching solution further contains a surfactant, and the surfactant is ethanol.

[0024] Furthermore, in step (3), when an etching solution is used, the specific steps of etching are: dispersing the silicon-carbon composite material of step (2) in an organic solvent, wherein the organic solvent is ethanol or isopropanol, and the solid-liquid ratio of the silicon-carbon composite material to the organic solvent is 1:40-50 g / mL, stirring and mixing at 20-30° C. for 30-40 min to obtain a Si-C suspension, introducing an etching solution into the Si-C suspension, pre-stirring for 3-8 min, and then etching for 1.5-2.5 h to obtain a two-dimensional porous silicon-carbon mixture.

[0025] Furthermore, in step (3), when HF-H 2 O 2 When the mixed steam is used for etching, the specific steps are as follows: the silicon-carbon composite material of step (2) is dispersed in a polytetrafluoroethylene reactor, and then 35%-45%wt hydrofluoric acid, 25%-35%wt hydrogen peroxide and ethanol are mixed in a volume ratio of 1.5-2:0.5-1:2-3 to form an etching solution, wherein the mass volume ratio of the silicon-carbon composite material, 35%-45%wt hydrofluoric acid, 25%-35%wt hydrogen peroxide and ethanol is 1g:1.5-2mL:0.5-1mL:2-3mL, and the solution is placed in a small reactor; the small reactor is placed in a large reactor, and heated in an oil bath at 95-105°C for 4-5h, and HF-H 2 O 2 Steam etching.

[0026] Furthermore, in step (3), when etching is performed using HF vapor, the specific steps are as follows: dispersing the silicon-carbon composite material of step (2) into a polytetrafluoroethylene reactor, and then mixing 35%-45%wt hydrofluoric acid and ethanol in a volume ratio of 1.5-2:2-3 to form an etching solution, wherein the mass volume ratio of the silicon-carbon composite material, 35%-45%wt hydrofluoric acid and ethanol is 1 g:1.5-2 mL:2-3 mL, and the solution is placed in a small reactor; placing the small reactor into a large reactor, heating in an oil bath at 95-105°C for 4-5 hours, and etching using HF vapor.

[0027] Furthermore, in step (4), the drying temperature is 65-75° C. and the drying time is 5-10 h.

[0028] A negative electrode material for a lithium-ion battery is composed of a porous silicon material prepared by any method described in the present invention.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) The method for preparing porous silicon by non-metal-assisted etching provided by the present invention does not require the use of precious metal catalysts, thus reducing production costs and avoiding the introduction of metal impurities. At the same time, carbon is introduced into the pores, thereby improving the conductivity of the silicon material during the cycle.

[0031] (2) The porous silicon material prepared by the present invention has a uniform pore structure, which can effectively alleviate the volume expansion of silicon during the charge and discharge process and improve the cycle stability of the electrode.

[0032] (3) The porous silicon material prepared by the present invention exhibits excellent electrochemical properties as a negative electrode material for lithium-ion batteries, including high specific capacity, good cycle stability and excellent rate performance.

[0033] (4) The method of the present invention has simple process, is easy to operate, has low cost, is suitable for large-scale production, and is conducive to market promotion. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is the SEM image of the porous silicon obtained in Example 1.

[0035] Figure 2 This is the SEM image of the porous silicon obtained in Example 2.

[0036] Figure 3 This is the SEM image of the porous silicon obtained in Example 3.

[0037] Figure 4 This is the SEM image of the porous silicon obtained in Example 4.

[0038] Figure 5 This is the SEM image of the porous silicon obtained in Example 5.

[0039] Figure 6 This is a SEM image of the silicon flake obtained in Comparative Example 1 without adding carbon.

[0040] Figure 7 1. High-angle dark field image of the pSi-C wafer in Example 1 and distribution diagram of related elements.

[0041] Figure 8 The atomic resolution high-angle dark field image of the thin slice in Example 1 and the enlarged images from the marked areas 1 and 2 and the corresponding reciprocal lattice patterns.

[0042] Fig. 9 This is the XRD pattern of the pSi-C flake in Example 1.

[0043] Fig.10 This is the thermogravimetric analysis curve of the pSi-C wafer in Example 1.

[0044] Fig.11is the BET N of the pSi-C flake in Example 1 2 Adsorption-desorption curve.

[0045] Fig.12 The pSi-C sheet in Example 1 is a lithium half-cell at 0.2 A g -1 The cycling performance under different current densities and the rate performance under different current densities.

[0046] Fig.13 Specific capacity-voltage curves of the pSi-C wafer in Example 1 at different cycles and rates.

[0047] Fig.14 The pSi-C sheet in Example 1 is a lithium iron phosphate (Si-Gr@C / / LiFePO 4 )’s full battery cycling performance at 0.2 C.

[0048] Fig.15 This is the rate performance of the full battery in Example 1. DETAILED DESCRIPTION

[0049] The following is a preferred implementation of the embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the embodiment of the present invention. These improvements and modifications are also considered to be within the scope of protection of the embodiment of the present invention.

[0050] Unless otherwise specified, the experimental methods used in the embodiments of the present invention are all conventional methods.

[0051] Unless otherwise specified, the materials, reagents, etc. used in the embodiments of the present invention can be obtained from commercial sources.

[0052] Example 1

[0053] A method for preparing porous silicon by carbon-assisted etching comprises the following steps:

[0054] (1) Silicon wafer pretreatment: Waste photovoltaic silicon wafers were ultrasonically cleaned with 0.3 wt% HCl, acetone, ethanol and deionized water in sequence, with each solvent ultrasonically cleaned for 1 h;

[0055] (2) Construction of carbon catalyst layer: 2 g of waste silicon pretreated in step (1) and 0.2 g of nanocarbon spheres with a diameter of about 20 nm were ball-milled. The ball milling process was carried out using zirconium dioxide balls and a ball mill jar. The mass ratio of balls to materials was 40:1. The ball mill was operated at a speed of 400 rpm for 12 h to uniformly disperse the carbon particles on the surface of the silicon particles to obtain a silicon-carbon composite material.

[0056] (3) Etching: 1 g of the silicon-carbon composite material prepared in step (2) was dispersed in 42 mL of ethanol and stirred at room temperature for 30 min to ensure uniformity, thereby obtaining a Si-C suspension; subsequently, 6 mL of hydrofluoric acid and 2 mL of hydrogen peroxide were mixed to form an etching solution; the etching solution was introduced into the Si-C suspension, initially stirred for 5 min, and then etched for 2 h, thereby forming a two-dimensional porous silicon-carbon mixture.

[0057] (4) Post-treatment: The two-dimensional porous silicon-carbon mixture prepared in step (3) was vacuum filtered and dried at 70 °C for 8 h to obtain the final product.

[0058] Figure 1 The pSi-C thin sheet obtained by the carbon-assisted etching method in Example 1 presents a nano-thin sheet structure with clear nanopores. The prepared porous silicon material has a uniform pore structure with a pore size of about 100-200 nm.

[0059] Figure 7 The distribution of various elements in the pSi-C flakes is shown, indicating that the carbon etchant is concentrated in the pores, proving the process of carbon-assisted etching.

[0060] Figure 8 This shows that the silicon structure is amorphous silicon wrapped in single crystal silicon. X-ray diffraction spectrum ( Fig. 9 ) indicates the crystalline structure of the silicon wafer. Thermogravimetric analysis in air showed a weight loss of 12.6% for pSi-C, corresponding to the content of nanocarbon ( Fig.10 ). Nitrogen adsorption-desorption measurements showed that the surface area of ​​pSi-C is 21.2 m 2 g -1 ( Fig.11 ). Pore size distribution analysis showed a wide range of pore sizes and a high concentration of mesopore diameters, consistent with the microscopic features.

[0061] The second cycle capacity of pSi-C is as high as 1654 mAh g -1 , the capacity retention rate after 100 cycles is 83% ( Fig.12 ). Representative constant current charge and discharge (GCD) curve ( Fig.13 ) shows a rapid increase in the Coulombic efficiency (CE) of pSi-C, reaching 83% in the first cycle and 95% in the second cycle, which is attributed to the rapid formation of a stable SEI. The full cell is composed of commercial LiFePO 4 The pSi-C / / LFP full cell exhibited 135, 132, 127, 122, 118, 114 and 90 mAh g at 0.2, 0.4, 0.6, 0.8, 1.0, 2.0 and 4.0 C, respectively.-1 The specific capacity ( Fig.14 The full cell also exhibited 137 mAh g at 0.2 C. -1 The high reversible capacity of the battery was 96.6% after 100 cycles. Fig.15 ).

[0062] Example 2

[0063] The difference from Example 1 is that in step 2, a layer of carbon particles is grown on the surface of silicon particles by chemical vapor deposition as a non-metallic catalyst layer. The specific steps are as follows: the pretreated silicon wafer is immersed in a 5 mol / L ferric chloride solution for 1 hour, taken out, dried, placed in a tube furnace, argon gas is introduced as a protective gas, and the temperature is raised to 900°C; then acetylene gas is introduced as a carbon source, and the reaction time is 30 minutes; after the reaction is completed, it is naturally cooled to room temperature to obtain an acetylene-derived carbon-modified silicon wafer. The remaining steps are the same as in Example 1.

[0064] Figure 2 This is a SEM image of the porous silicon obtained in Example 2, showing a nanosheet structure with clear nanopores.

[0065] Example 3

[0066] The difference from Example 1 is that ethanol is replaced by isopropanol in step 3. The remaining steps are the same as in Example 1.

[0067] Figure 3 This is a SEM image of the porous silicon obtained in Example 3, showing a nanosheet structure with clear nanopores.

[0068] Example 4

[0069] The difference from Example 1 is that in the etching process in step 3, 1 g of the silicon-carbon composite material of step (2) is dispersed into a 100 mL polytetrafluoroethylene reactor, and then 1.5 mL of 40% wt hydrofluoric acid solution, 0.5 mL of 30% wt hydrogen peroxide solution and 2 mL of ethanol are mixed to form an etching solution, which is then placed in a 5 mL small reactor; the small reactor is placed in a 100 mL reactor, heated in an oil bath at 100°C for 4 h, and HF-H 2 O 2 Steam etching. The remaining steps are the same as in Example 1.

[0070] Figure 4 The SEM image of the porous silicon obtained in Example 4 shows a nanosheet structure with clear nanopores.

[0071] Example 5

[0072] The difference from Example 4 is that in the etching process in step 3, no hydrogen peroxide solution is added, and HF vapor etching is used. The remaining steps are the same as in Example 4.

[0073] Figure 5 This is a SEM image of the porous silicon obtained in Example 5, showing a nanosheet structure with clear nanopores.

[0074] The porous silicon prepared in Examples 2 to 5 can be applied to negative electrode materials of lithium-ion batteries.

[0075] In summary, the present invention does not require the use of precious metal catalysts or other metal catalysts, has a simple process and low cost, and can directly etch silicon particles or silicon plates into porous silicon structures; the prepared porous silicon material has a uniform pore structure, which can effectively alleviate the volume expansion of silicon during the charging and discharging process, and the carbon in the pores can effectively enhance the conductivity of the electrode and improve the cycle stability of the electrode. The porous silicon material is applied to the negative electrode material of lithium-ion batteries, showing excellent electrochemical properties, including high specific capacity, good cycle stability and excellent rate performance.

[0076] Comparative Example 1

[0077] This comparative example is based on Example 1, but no carbon is added. Figure 6 This is a SEM image of a silicon wafer without adding carbon in Comparative Example 1. After not adding carbon, no porous structure is present, which shows the important role of carbon etchant in the formation process of porous silicon.

[0078] The above embodiments are only used to illustrate the present invention, rather than to limit the present invention. Those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention, and these modifications and variations should all fall within the scope defined in the claims of the present invention.

Claims

1. A method for preparing porous silicon carbon by carbon-assisted etching, characterized in that: The following steps are involved: (1) Cleaning the waste photovoltaic silicon wafers by ultrasonic treatment to obtain pretreated silicon wafers; (2) reacting the pretreated silicon wafer in step (1) with a carbon source material to obtain a silicon-carbon composite material; (3) etching the silicon-carbon composite material obtained in step (2) to obtain a porous silicon-carbon mixture; (4) vacuum filtering and drying the porous silicon-carbon mixture in step (3) to obtain a final product; Step (2), the carbon source material is one or more of nano-carbon balls, carbon nanotubes, graphene, and activated carbon, and the specific steps of step (2) are: ball milling the pretreated silicon wafer and the carbon source material in a mass ratio of 1:0.08-0.12, using zirconium dioxide balls and a ball milling jar for the ball milling process, the mass ratio of zirconium dioxide balls to materials is 30-50:1, and ball milling is performed at 300-500 rpm for 10-15 hours to obtain a silicon-carbon composite material; Step (3), the etching method is to use a solution method for etching; the etching solution used in the etching contains hydrofluoric acid and an oxidant, the volume ratio of the hydrofluoric acid to the oxidant is 3:0.5~1.5, and the oxidant is at least one of H2O2 and HNO3; when the solution method is used, the specific steps of the etching are: dispersing the silicon-carbon composite material of step (2) in an organic solvent, the organic solvent is ethanol or isopropanol, the solid-liquid ratio of the silicon-carbon composite material to the organic solvent is g / mL of 1:40~50, stirring and mixing at 20~30°C for 30~40min to obtain a Si-C suspension, introducing the etching solution into the Si-C suspension, pre-stirring for 3~8min, and then etching for 1.5~2.5h to obtain a two-dimensional porous silicon-carbon mixture.

2. The method for preparing porous silicon carbon by carbon-assisted etching according to claim 1, characterized in that: Step (1), the ultrasonic treatment is: ultrasonically cleaning the waste photovoltaic silicon wafers with 0.2%~0.4%wt HCl solution, acetone, ethanol and deionized water in sequence, with each solvent ultrasonically cleaning for 0.8~1.2h.

3. The method for preparing porous silicon carbon by carbon-assisted etching according to claim 1, characterized in that: In step (2), the carbon source material is acetylene gas. The specific steps of step (2) are: immersing the pretreated silicon wafer in a 4-6 mol / L ferric chloride solution for 0.8-1.2 hours, taking it out, drying it, placing it in a tube furnace, introducing argon as a protective gas, and heating it to 850-950° C.; then introducing acetylene gas as a carbon source, and the reaction time is 20-40 minutes; after the reaction is completed, naturally cooling it to room temperature to obtain a silicon wafer modified with acetylene-derived carbon, that is, a silicon-carbon composite material.

4. The method for preparing porous silicon carbon by carbon-assisted etching according to claim 1, characterized in that: In step (4), the drying temperature is 65-75°C and the drying time is 5-10 hours.

5. A negative electrode material for a lithium ion battery, characterized in that: The porous silicon carbon is obtained by the preparation method according to any one of claims 1 to 4.

Images