A method for preparing silicon-carbon composite material using photovoltaic squared wet silicon powder

Abstract

The present invention discloses a method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder. The method comprises purifying the photovoltaic squared wet silicon powder by sulfuric acid calcination to obtain purified silicon powder; purifying waste power battery graphite negative electrodes by sulfuric acid and hydrogen peroxide to obtain purified graphite; and high-energy ball milling the purified silicon powder and purified graphite powder to obtain the silicon-carbon composite material. The method utilizes photovoltaic squared wet silicon powder and waste lithium battery graphite negative electrode powder as the silicon and carbon sources for the silicon-carbon negative electrode material, effectively reducing the production cost of the silicon-carbon negative electrode while also addressing solid waste disposal issues in the photovoltaic and power battery recycling industries, thereby achieving significant economic and environmental benefits.

Description

Technical Field

[0001] The present invention relates to the field of comprehensive utilization technology, and in particular to a method for preparing a silicon-carbon composite material by utilizing photovoltaic squared wet silicon powder. Background Art

[0002] Carbon materials have good conductivity and stability, and can provide a good electron conduction path, making lithium ions more stable during the charge and discharge process. However, their theoretical capacity (372mAh / g) is limited and has gradually failed to meet market demand. Silicon materials, which have a similar discharge platform to graphite, have a higher capacity (4200mAh / g, Li22Si5), but have poor conductivity, which is not conducive to lithium ion diffusion and electron transmission. The composite of silicon and carbon materials effectively solves the defects of single negative electrode materials and combines the excellent properties of both. It is considered to be the most promising next-generation lithium-ion battery negative electrode material.

[0003] Mechanical ball milling, one of the main methods for preparing silicon-carbon composites, often uses silicon powder (metallurgical-grade silicon) as the silicon source and graphite as the carbon source. According to data from the Shanghai Nonferrous Metals Network, in August 2023, the price of silicon powder (≥99.2%) exceeded 14,000 yuan / ton, and the average price of low-end artificial graphite was 24,000 yuan / ton. If the cost of silicon powder and graphite raw materials can be reduced, it will help promote the industrialization of silicon-carbon anode materials.

[0004] Diamond wire multi-wire cutting is the mainstream technology for photovoltaic silicon wafer cutting. According to the environmental impact assessment report of the silicon wafer production enterprise, the squaring process will result in 5-10% silicon loss. This loss is dispersed in the cutting coolant in the form of silicon powder. The wet silicon powder obtained by cooling liquid filtration is a general solid waste, mainly containing silicon powder, diamond powder and carbon steel debris dropped by diamond wire grinding, and organic matter from the diamond wire cutting fluid (polyethylene glycol, chelating agent, organic alcohol, etc.). According to literature reports, the silicon powder in the wet silicon powder has the characteristics of high purity (dry basis, more than 90%) and small particle size (micro-nano level). If it is purified and recycled to prepare silicon-carbon anodes, it can not only effectively reduce the production cost of silicon-carbon anodes, but also solve the disposal problem of waste silicon powder in the photovoltaic industry, thereby bringing good economic and environmental benefits. Chinese patent application CN 201811063650.5 discloses a method for preparing lithium battery negative electrode materials using waste silicon powder cut by diamond wire cutting. Through purification, surface modification, consistency treatment and other processes, silicon material that meets the requirements of the lithium battery silicon-carbon negative electrode preparation process is prepared, realizing the reuse of diamond wire cutting waste. However, the purification process uses SDBS (sodium dodecylbenzenesulfonate) as a surfactant. This substance has strong foaming ability, requires many washing times (5 to 20 times), and is difficult to decompose at low temperatures (180 to 260°C), thereby affecting the electrical properties of the silicon-carbon negative electrode material.

[0005] The graphite negative electrode of power lithium batteries is artificial graphite, and its preparation usually requires high temperatures of 2000-3000°C to achieve graphitization, a process that accounts for about 50% of the total cost. However, the graphite structure in the graphite negative electrode powder of waste power lithium batteries is orderly and does not require further graphitization. In addition, the graphite content is high (more than 80%), far exceeding the grade of graphite ore (about 10%). If it can be reused, it will help save energy and reduce production costs. Chinese patent application CN202110217443.6 discloses a method and application of preparing silicon-carbon composite materials using waste lithium-ion battery negative electrodes. This method uses graphite purified from waste lithium-ion battery negative electrodes and carbonized nanosilicon to prepare silicon-carbon composite materials. The resulting material has good electrochemical properties; however, the cost of nanosilicon raw materials has not been solved, and production costs need to be further reduced. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing silicon-carbon composite materials using photovoltaic squared wet silicon powder in order to solve the above problems. The present invention uses photovoltaic squared wet silicon powder and waste lithium battery graphite negative electrode powder as the silicon source and carbon source of silicon-carbon negative electrode materials. While effectively reducing the production cost of silicon-carbon negative electrodes, it can also solve the solid waste disposal problem in the photovoltaic industry and power battery recycling industry, thereby bringing good economic and environmental benefits.

[0007] The present invention achieves the above-mentioned purpose through the following technical solutions:

[0008] A method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder comprises the following steps:

[0009] A. Purification of photovoltaic-cut wet silicon powder: The photovoltaic-cut wet silicon powder is mixed with sulfuric acid and subjected to sulfate roasting. The roasted product is water-leached, and polyethylene glycol and a chelating agent are added. After the water-leaching reaction is completed, solid-liquid separation is performed to obtain filter residue S1 and filtrate L1. The filter residue S1 is washed with water until neutral and dried to obtain purified silicon powder;

[0010] B. Graphite negative electrode purification: The waste lithium battery graphite negative electrode powder is placed in a mixed acid solution of sulfuric acid and hydrogen peroxide for acid leaching, polyethylene glycol and a chelating agent are added, and after the acid leaching reaction is completed, solid-liquid separation is performed to obtain filter residue S2 and filtrate L2. The filter residue S2 is washed with water until neutral and calcined to obtain purified graphite;

[0011] C. Preparation of silicon-carbon composite material: Purified silicon powder and purified graphite are mixed in proportion, and high-energy ball milling is performed to obtain the silicon-carbon composite material; the mass percentage of purified silicon powder and purified graphite is 1-10%:99-90%;

[0012] The ball mill speed is 1000-2500r / min, and the ball milling time is 1-10h.

[0013] A further solution is that in step A, the amount of sulfuric acid added is 5-20% of the dry mass of the photovoltaic square wet silicon powder.

[0014] A further solution is that in step A, the sulfuric acid roasting temperature is 200-400° C. and the roasting time is 1-6 hours.

[0015] A further solution is that in step A, the water immersion temperature is 40-80° C., and the water immersion time is 1-6 hours; and the washing water of the filter residue S1 is recycled for the water immersion reaction in step A.

[0016] A further solution is that in step A, the amount of polyethylene glycol added is 5-10% of the dry basis mass of the photovoltaic cut wet silicon powder; the chelating agent is EDTA-2Na and / or DTPA, and the amount of the chelating agent added is 0.5-1% of the dry basis mass of the photovoltaic cut wet silicon powder.

[0017] A further solution is that in step B, the mixed acid solution is a mixture of 5 mol / L sulfuric acid and 5 mol / L hydrogen peroxide in a ratio of 1:1.

[0018] A further solution is that in step B, the amount of polyethylene glycol added is 5-10% of the mass of the waste lithium battery negative electrode powder; the chelating agent is EDTA-2Na and / or DTPA, and the amount of the chelating agent added is 0.5-1% of the mass of the waste lithium battery negative electrode powder.

[0019] A further solution is that in step B, the acid leaching reaction temperature is 60-80° C., and the acid leaching reaction time is 1-10 hours; and the filter residue S2 washing water is recycled for preparing the acid solution in step B.

[0020] A further solution is that in step B, the calcination temperature is 300-500° C. and the calcination time is 0.5-2 h.

[0021] Another aspect of the present invention also provides a silicon-carbon composite material obtained by the above preparation method;

[0022] In another aspect, the present invention provides uses of the silicon-carbon composite material obtained by the above preparation method.

[0023] The beneficial effects of the present invention are:

[0024] 1. The present invention uses photovoltaic square wet silicon powder and waste lithium battery graphite negative electrode powder as the silicon source and carbon source of the silicon-carbon negative electrode material. While effectively reducing the production cost of the silicon-carbon negative electrode, it can also solve the solid waste disposal problem in the photovoltaic industry and power battery recycling industry, thereby bringing good economic and environmental benefits.

[0025] 2. Polyethylene glycol is one of the organic components of diamond wire cutting fluid. Using it as a dispersant in the purification process can avoid the introduction of new impurities.

[0026] 3. Waste silicon powder and waste graphite powder contain a variety of metal impurities. The addition of a strong chelating agent during the purification process reduces the presence of adsorbable metals on the surface and between layers of the powder, and improves the removal efficiency of metal impurities. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the following briefly introduces the practical drawings required in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0028] Figure 1 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0029] To make the objectives, technical solutions, and advantages of the present invention more apparent, the technical solutions of the present invention will be described in detail below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other implementations obtained by those of ordinary skill in the art without inventive effort are within the scope of protection of the present invention.

[0030] Example 1

[0031] Photovoltaic squared wet silicon powder was obtained from Sichuan JinkoSolar Co., Ltd., and its composition is shown in Table 1. Graphite anode powder from waste power lithium batteries was obtained from Jiangxi Gerun New Materials Co., Ltd.;

[0032] A. Purification of wet silicon powder:

[0033] 100g of wet silicon powder was thoroughly mixed with 9g of concentrated sulfuric acid and calcined at 300°C for 2h. The calcined product was cooled, crushed, and placed in a 1000mL beaker. 500mL of water, 5g of polyethylene glycol, and 0.5g of EDTA-2Na were added to the beaker. After immersion in water at 80°C for 4h, solid-liquid separation was performed to obtain filter residue 1 and filtrate 1. The obtained filter residue 1 was washed with water twice (the washing water was neutral at this time) and dried to obtain purified silicon powder 1. The washing water of the obtained filter residue 1 was recycled for the water immersion reaction.

[0034] B. Graphite anode purification:

[0035] Prepare a mixed acid solution of 5 mol / L sulfuric acid and 5 mol / L hydrogen peroxide in a 1:1 ratio. Place 100 g of spent lithium-ion battery graphite negative electrode powder in a 1000 mL beaker and mix with 500 mL of the mixed acid solution. Add 5 g of polyethylene glycol and 0.5 g of EDTA-2Na. React at 80°C for 4 h, then separate the solid and liquid to obtain residue S2 and filtrate L2. Wash residue S2 with water four times (the wash water is neutral at this point) and calcine at 400°C for 0.5 h to obtain purified graphite 1. The wash water from residue 2 is used to prepare the acid solution.

[0036] C. Preparation of silicon-carbon composite materials:

[0037] The purified silicon powder 1 obtained in step A and the purified graphite 1 obtained in step B were subjected to high-energy ball milling at a specific mass ratio (5%:95%). Dry milling was employed in a 100 mL ball mill lined with zirconium oxide. Zirconia beads with diameters of 5, 8, 10, and 15 mm were used in a mass ratio of 2:2:2:1. The bead-to-material ratio (bead-to-material ratio) was 50:1. The mill speed was 1400 rpm, and the milling time was 2 hours. The resulting silicon-carbon composite exhibited a reversible specific capacity of 587 mA·h / g after 100 cycles at a current density of 0.5 A / g.

[0038] Table 1 Comparison of purification effects of wet silicon powder in Example 1 (%)

[0039] name silicon iron aluminum calcium sodium Moisture C Wet silica fume 90.71 0.05 0.02 0.05 0.01 9.13 0.1 Purified silicon powder 1 99.99 0.001 / 0.007 / / /

[0040] Note: “ / ” means not detected, the same below.

[0041] Wet silicon fume mainly contains silicon powder, diamond powder and carbon steel scrap removed from diamond wire grinding, as well as organic matter from the diamond wire cutting fluid (polyethylene glycol, chelating agents, organic alcohols, etc.). The rationale for using sulfuric acid roasting to remove impurities is that the metallic impurities (aluminum, calcium, sodium, etc.) contained in the diamond powder and carbon steel scrap removed from diamond wire grinding react with concentrated sulfuric acid to form readily soluble / dispersible sulfates, while excess concentrated sulfuric acid reacts with non-metallic impurities (carbon) to form carbon dioxide (reaction mechanism shown below). Furthermore, high temperatures can decompose organic matter in the diamond wire cutting fluid, but silicon fume is unaffected by these conditions.

[0042] C + 2H2SO4 (concentrated) = CO2 + 2SO2 + 2H2O (1)

[0043] As shown in Table 2, at 298 K, the Gibbs free energy change (ΔG) of the reaction between carbon and concentrated sulfuric acid is less than zero. As the calcination temperature increases, the Gibbs free energy change decreases, indicating that the reaction can proceed at room temperature. As the calcination temperature increases, the reaction rate increases.

[0044] Table 2 Gibbs free energy function of carbonization reaction at different temperatures

[0045] temperature C <![CDATA[H2SO4]]> <![CDATA[CO2]]> <![CDATA[SO2]]> <![CDATA[H2O]]> ΔG 298K -1.71 -860.77 -457.21 -370.79 -298.08 -71.7 400K -2.45 -879.02 -479.58 -396.71 -317.84 -148.19 600K -4.79 -913.74 -526.58 -450.77 -359.1 -314.05

[0046] Table 3 Comparison of purification effects of waste power lithium battery graphite negative electrode in Example 1 (%)

[0047]

[0048] Table 3 shows that the main impurities in this graphite negative electrode powder are aluminum, copper, nickel, cobalt, and manganese, indicating that the graphite negative electrode powder comes from spent ternary power lithium batteries. The aluminum, nickel, cobalt, and manganese come from the positive electrode current collector and positive electrode powder, while the copper comes from the negative electrode current collector. According to the principle of displacement reaction, aluminum, nickel, cobalt, and manganese react with sulfuric acid to form readily soluble / soluble sulfates, but copper does not undergo displacement reaction with acid. Therefore, the graphite purification process uses a mixed acid of sulfuric acid and hydrogen peroxide as a leaching agent, utilizing a redox reaction to convert metallic copper into copper sulfate. The reaction mechanism is as follows.

[0049] Cu+H2SO4+H2O2=CuSO4+2H2O(2)

[0050] Example 2

[0051] Photovoltaic squared wet silicon powder was obtained from Sichuan JinkoSolar Co., Ltd., and its composition is shown in Table 4. Graphite anode powder from waste power lithium batteries was obtained from Jiangxi Gerun New Materials Co., Ltd.

[0052] A. Purification of wet silicon powder:

[0053] 100g of wet silicon powder was thoroughly mixed with 15g of concentrated sulfuric acid and calcined at 260°C for 2h. The calcined product was cooled, crushed, and placed in a 1000mL beaker. 500mL of water, 10g of polyethylene glycol, and 0.5g of DTPA were added to the beaker. The mixture was immersed in water at 80°C for 4h, followed by solid-liquid separation to obtain filter residue 1 and filtrate 1. The filter residue 1 was washed twice with water (the wash water was neutral at this point) and dried to obtain purified silicon powder 1. The wash water from the filter residue 1 was recycled for the water immersion reaction to conserve water.

[0054] B. Graphite anode purification:

[0055] Prepare a 1:1 mixed acid solution of 5 mol / L sulfuric acid and 5 mol / L hydrogen peroxide. Place 100 g of spent lithium-ion battery graphite negative electrode powder in a 1000 mL beaker and mix with 500 mL of the mixed acid solution. Add 10 g of polyethylene glycol and 0.5 g of DTPA. React at 80°C for 4 hours, then separate the solid and liquid to obtain residue S2 and filtrate L2. Wash residue S2 four times with water (the wash water is neutral at this point) and calcine at 400°C for 0.5 hour to obtain purified graphite 2. The wash water from residue 2 is used to prepare the acid solution to conserve water.

[0056] C. Preparation of silicon-carbon composite materials:

[0057] The purified silicon powder 2 obtained in step A and the purified graphite 2 obtained in step B were subjected to high-energy ball milling at a specific mass ratio (5%:95%). Dry milling was employed in a 100 mL ball mill lined with zirconium oxide. Zirconia beads with diameters of 5, 8, 10, and 15 mm were used in a mass ratio of 2:2:2:1. The bead-to-material ratio (bead-to-material ratio) was 50:1. The mill speed was 1400 rpm, and the milling time was 2 hours. The resulting silicon-carbon composite exhibited a reversible specific capacity of 602 mA·h / g after 100 cycles at a current density of 0.5 A / g.

[0058] Table 4 Comparison of purification effect of wet silicon powder in Example 2 (%)

[0059] name silicon iron aluminum calcium sodium Moisture C Wet silica fume 90.71 0.05 0.02 0.05 0.01 9.13 0.1 Purified silicon powder 2 99.99 / / 0.005 / / /

[0060] Table 5 Comparison of purification effect of waste power lithium battery graphite negative electrode in Example 2 (%)

[0061]

[0062] The above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with the technical field can easily think of changes or replacements within the technical scope disclosed by the present invention, which should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner unless there is any contradiction. In order to avoid unnecessary repetition, the present invention will no longer describe various possible combinations separately. In addition, the various different embodiments of the present invention can also be arbitrarily combined. As long as they do not violate the ideas of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. A method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder, characterized in that: The following steps are involved: A. Purification of photovoltaic-cut wet silicon powder: The photovoltaic-cut wet silicon powder is mixed with sulfuric acid and subjected to sulfate roasting. The roasted product is water-leached, and polyethylene glycol and a chelating agent are added. After the water-leaching reaction is completed, solid-liquid separation is performed to obtain filter residue S1 and filtrate L1. The filter residue S1 is washed with water until neutral and dried to obtain purified silicon powder; B. Graphite negative electrode purification: The waste lithium battery graphite negative electrode powder is placed in a mixed acid solution of sulfuric acid and hydrogen peroxide for acid leaching, polyethylene glycol and a chelating agent are added, and after the acid leaching reaction is completed, solid-liquid separation is performed to obtain filter residue S2 and filtrate L2. The filter residue S2 is washed with water until neutral and calcined to obtain purified graphite; C. Preparation of silicon-carbon composite material: Purified silicon powder and purified graphite are mixed in proportion, and high-energy ball milling is performed to obtain the silicon-carbon composite material; The mass percentage of purified silicon powder and purified graphite is 1-10%:99-90%; The ball mill speed is 1000-2500r / min, and the ball milling time is 1-10h.

2. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step A, the amount of sulfuric acid added is 5-20% of the dry weight of the photovoltaic square wet silicon powder.

3. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step A, the sulfation roasting temperature is 200-400° C., and the roasting time is 1-6 hours.

4. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step A, the water immersion temperature is 40-80° C., and the water immersion time is 1-6 hours; the filter residue S1 washing water is recycled for the water immersion reaction in step A.

5. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In step A, the amount of polyethylene glycol added is 5-10% of the dry basis mass of the photovoltaic square wet silicon powder; the chelating agent is EDTA-2Na and / or DTPA, and the amount of the chelating agent added is 0.5-1% of the dry basis mass of the photovoltaic square wet silicon powder.

6. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In step B, the mixed acid solution is a mixture of 5 mol / L sulfuric acid and 5 mol / L hydrogen peroxide in a ratio of 1:

1.

7. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step B, the amount of polyethylene glycol added is 5-10% of the mass of the waste lithium battery negative electrode powder; the chelating agent is EDTA-2Na and / or DTPA, and the amount of the chelating agent added is 0.5-1% of the mass of the waste lithium battery negative electrode powder.

8. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step B, the acid leaching reaction temperature is 60-80° C., and the acid leaching reaction time is 1-10 hours; the filter residue S2 washing water is recycled for preparing the acid solution in the step B.

9. The method for preparing a silicon-carbon composite material using photovoltaic squared wet silicon powder according to claim 1, wherein: In the step B, the calcination temperature is 300-500° C., and the calcination time is 0.5-2 hours.

10. The silicon-carbon composite material obtained by the preparation method according to any one of claims 1 to 9.

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