A method for preparing a composite silicon-based anode material

Abstract

This invention discloses a method for preparing a composite silicon-based anode material, belonging to the field of lithium-ion battery anode materials. The specific preparation method is as follows: purified silicon powder and graphene are milled and set aside. The milled silicon and graphene are mixed and then subjected to segmented milling to embed nano-silicon onto the graphene surface, resulting in a graphene / silicon slurry. A pyrolytic carbon source is added to the slurry, followed by spray drying and granulation. The resulting material is then subjected to high-temperature carbonization to obtain a "flower cluster" silicon-based anode. This invention uniformly embeds nano-silicon onto the graphene surface, combined with surface carbon coating, which alleviates the volume expansion of silicon and improves electronic conductivity. The prepared silicon-based anode material has a "flower cluster" structure, solving the problem of low lithium-ion diffusion rate caused by severe nano-silicon agglomeration. The synthesized composite material has a long cycle life, excellent rate performance, a short process flow, and kilogram-level production capacity, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to a method for preparing a composite silicon-based anode material, in the field of lithium-ion battery anode materials. Background Technology

[0002] With the rapid development and continuous expansion of the new energy vehicle industry, the development of high-power, high-capacity, and high-safety battery systems is urgently needed. Traditional graphite anodes, due to their relatively low theoretical specific capacity (372 mAh / g), can no longer meet the ever-increasing demand for high-energy-density batteries. In the search for alternative materials, many attempts have been made, and numerous new high-energy-density anode materials have been developed and tested, such as lithium metal anodes, alloy anodes, metal oxide anodes, and metal sulfide anodes. However, most of these new materials, while possessing high performance, also have certain defects, thus limiting their large-scale application. In anode material research, silicon, as the second most abundant element in the Earth's crust, has advantages in terms of reserves, cost, and ecology, making it considered the most attractive material and a hot topic in anode material research in recent years. It is expected to replace carbon anode materials as the next generation of high-performance lithium battery anode materials. However, the huge volume expansion during the lithium insertion / extraction process of silicon-based anode materials leads to the breakage and pulverization of active particles, unstable and continuously growing surface SEI film structures, and severe electrode structure collapse, resulting in rapid degradation of the electrochemical performance of silicon anodes and low cycle life.

[0003] Nanomaterials are an effective means of modifying and optimizing silicon-based anodes. Nanoscale silicon particles are effective in addressing the volume expansion of silicon-based anodes. Nanoscale silicon particles have a higher specific surface area and their surface atoms have a higher average binding energy, allowing them to better release stress during volume expansion and preventing structural collapse. However, silicon nanoparticles still have drawbacks in lithium-ion battery applications: firstly, their large specific surface area requires more electrolyte to form an SEI film; secondly, the small size of silicon nanospheres makes them prone to agglomeration, leading to low lithium-ion diffusion rates; and thirdly, the preparation cost of silicon nanoparticles is very high. Summary of the Invention

[0004] To address the problems existing in current silicon anode materials, this invention provides a method for preparing a composite silicon-based anode material, the specific preparation method comprising the following steps:

[0005] (1) Silicon powder is obtained by drying and crushing silicon raw materials. The silicon powder is placed in HF-alcohol solution for stirring and dispersion, solid-liquid separation, and washing of the solid to obtain purified silicon powder.

[0006] (2) The purified silicon powder obtained in step (1) is stirred evenly in an alcohol solution and then sand-milled to obtain a slurry containing nano-silicon.

[0007] (3) After stirring the graphene in the alcohol solution until it is uniform, it is then sand-milled.

[0008] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling to obtain graphene / silicon slurry.

[0009] (5) Add pyrolytic carbon source to the graphene / silicon slurry in step (4), perform spray drying and granulation, and then perform high-temperature carbonization on the obtained material to obtain a novel composite structure high-performance silicon-based anode material.

[0010] Preferably, the silicon raw material in step (1) is one of the following: silicon waste recycled from the photovoltaic industry, silicon recycled from solar photovoltaic modules, industrial silicon, or commercial silicon powder of different purities.

[0011] Preferably, in step (1), the liquid-solid ratio of HF-alcohol solution to silicon powder is (10-500):1, in mL:g; in the HF-alcohol solution, the HF concentration is 0.1-20 mol / L, the alcohol concentration is 0.1-20 mol / L, and the alcohol is one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol mixed in any proportion.

[0012] Preferably, the stirring and dispersion time in step (1) is 10–720 min.

[0013] Preferably, in step (2), the alcohol solution contains one or more of the following alcohols: methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol. The liquid-solid ratio of the alcohol solution to the purified silicon powder is (10-500):1 (mL:g). The speed of the sand mill is 1000-3000 r / min, and the sand milling time is 1-48 h.

[0014] Preferably, in step (3), the alcohol solution contains one or more of the following alcohols: methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and ethylene alcohol. The liquid-solid ratio of the alcohol solution to the graphene powder is (10-500):1, with units of mL:g. The rotation speed of the sand mill during the sand milling of graphene is 1000-3000 r / min, and the sand milling time is 1-48 h.

[0015] Preferably, the segmented sand milling in step (4) can be a three-stage sand milling, wherein the first stage sand milling conditions are 1000-1300 r / min and sand milling for 1-1.5 h; the second stage sand milling conditions are 2000-2200 r / min and sand milling for 1.5-3 h; and the third stage sand milling conditions are 2700-2800 r / min and sand milling for 1-3 h.

[0016] Preferably, the mass percentage of silicon in the graphene / silicon slurry formed in step (4) is 1% to 90%.

[0017] Preferably, in step (5), the mass fraction of carbon is 1% to 70% of the silicon-based anode material, and the carbon is added in the form of a carbon source, which is one or more of polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, sugar materials, and aromatic compounds; during the spray drying process, the feed rate is 1 to 200 ml / min, and the spray outlet temperature is 80 to 200°C.

[0018] Preferably, in step (5), the heating rate during carbonization is 1 to 30 °C / min, the temperature of high-temperature heat treatment is 600 to 1600 °C, and the time is 0.5 to 24 h.

[0019] Beneficial effects of the present invention

[0020] (1) The silicon-based anode material prepared by the present invention is a "flower cluster" graphene / silicon / carbon composite material through spray drying and high-temperature pyrolysis. This structure effectively avoids the agglomeration of nano-silicon and greatly shortens the lithium-ion transport path. At the same time, the material has a loose structure supported by graphene inside and a dense carbon shell provided by pyrolysis carbon outside, forming a gradient density structure, which greatly alleviates the volume expansion of the composite material. The synthesized composite material has an ultra-long cycle life and ultra-high rate performance, which is suitable for the requirements of anode materials (instantaneous high rate discharge) of UAVs (military and civilian).

[0021] (2) A segmented sand milling process is adopted, with different speed and time settings for each segment, which enables precise control of material particles. The segmented sand milling process can not only significantly improve the uniformity and dispersion of materials, but also effectively reduce heat accumulation during the grinding process, reduce damage to materials, and ultimately improve product performance and quality.

[0022] (3) By utilizing the high conductivity of graphene and the fact that its morphology is not easily altered during the sand milling process, graphene is combined with silicon, which greatly improves the electronic conductivity of the composite material. The segmented sand milling method ensures that the silicon material is uniformly embedded on the graphene surface, suppressing the volume expansion of silicon during cycling. Combined with carbon coating, direct contact between silicon and electrolyte is avoided, thus improving the coulombic efficiency of the composite material.

[0023] (4) A wide range of silicon materials can be selected. Commercially produced silicon powder of different particle sizes can be used, or recycled silicon waste from diamond wire cutting in the photovoltaic industry and silicon recycled from solar photovoltaic modules can be used as raw material sources to reduce the cost of material preparation. Attached Figure Description

[0024] Figure 1 This is a SEM image of the composite material synthesized in Example 1.

[0025] Figure 2 This is a SEM image of the composite material synthesized in Example 2.

[0026] Figure 3 This is a comparison graph of the electrochemical properties of the composite materials synthesized in Example 3.

[0027] Figure 4 This is a graph showing the long-cycle performance of the composite material synthesized in Example 4.

[0028] Figure 5 The graph shows the rate performance of the composite materials synthesized in Example 1 and Comparative Example 1.

[0029] Figure 6 This is a comparison of the cycling performance of the materials synthesized in Example 1 and Comparative Example 2.

[0030] Figure 7 This is a comparison of the cycling performance of the composite materials synthesized in Comparative Example 3 and Example 2. Detailed Implementation

[0031] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments. However, the following embodiments are merely simple examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be determined by the claims.

[0032] Example 1

[0033] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0034] (1) Using commercially produced silicon powder as raw material, the silicon powder was placed in an HF-ethanol solution and ultrasonically dispersed for 80 min to remove the oxide layer and other impurities on the surface of the silicon material. In the HF-ethanol solution, the concentration of HF was 1 mol / L and the concentration of ethanol was 1 mol / L. The liquid-solid ratio of the HF-ethanol solution system to the silicon powder was 10:1, with the unit being mL:g. After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0035] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 100:1, and the unit is mL:g. The speed of the sand mill is 2800r / min and the milling time is 3h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0036] (3) After mixing graphene in an ethanol solution, the graphene to ethanol liquid-solid ratio is 30:1 (mL:g), the speed of the mill is 1500r / min, and the milling time is 10h.

[0037] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1000 r / min and the time is 1 h to make the nano-silicon and graphene mix evenly. The second sand milling speed is 2000 r / min and the time is 2 h to make the silicon and graphene initially bond. The third sand milling speed is 2700 r / min and the time is 2 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 70%.

[0038] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 20% of the silicon-based anode material. The carbon is added in the form of glucose. During the spray drying process, the feed rate is 20 ml / min, the spray outlet temperature is 110°C, and the obtained material is subjected to high-temperature carbonization. The heating rate during the carbonization process is 5°C / min, the high-temperature heat treatment temperature is 900°C, and the holding time is 2 hours.

[0039] like Figure 1 The image shown is a SEM image of the silicon-based composite material prepared in Example 1, which shows a "flower-like" structure with a dense carbon shell on the outside and a loose graphene / silicon structure on the inside. This structure can alleviate volume expansion and improve the rate performance of the composite material.

[0040] Example 2

[0041] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0042] (1) Using photovoltaic silicon cutting waste as raw material, silicon powder was placed in HF-ethanol solution and ultrasonically dispersed for 100 min to remove the oxide layer and other impurities on the surface of silicon material. The HF concentration was 2 mol / L, the ethanol concentration was 2 mol / L, and the liquid-solid ratio of the HF-ethanol solution system to silicon powder was 20:1 (mL:g). After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0043] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 40:1, and the unit is mL:g. The speed of the sand mill is 2300r / min and the milling time is 6h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0044] (3) After mixing graphene in an ethanol solution, the graphene to ethanol liquid-solid ratio is 40:1 (mL:g), the speed of the mill is 2300r / min, and the milling time is 4h.

[0045] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1100 r / min and the time is 1 h to make the silicon and graphene mix evenly. The second sand milling speed is 2100 r / min and the time is 2 h to make the silicon and graphene initially bond. The third sand milling speed is 2700 r / min and the time is 2 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 45%.

[0046] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 20% of the silicon-based anode material. The carbon is added in the form of glucose. During the spray drying process, the feed rate is 15 ml / min, the spray outlet temperature is 90°C, and the obtained material is subjected to high-temperature carbonization. The heating rate during the carbonization process is 6°C / min, the high-temperature heat treatment temperature is 1000°C, and the holding time is 1.5 h.

[0047] like Figure 2 The image shown is a SEM image of the silicon-based composite material prepared in Example 2, which shows a "flower cluster" structure.

[0048] Example 3

[0049] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0050] (1) Using photovoltaic silicon cutting waste as raw material, silicon powder was placed in HF-methanol solution and ultrasonically dispersed for 45 min to remove the oxide layer and other impurities on the surface of silicon material. The concentration of HF was 1.5 mol / L, the concentration of methanol was 1.5 mol / L, and the liquid-solid ratio of HF-methanol solution system to silicon powder was 20:1, with units of mL:g. After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0051] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of methanol solution to silicon powder is 50:1 (mL:g). The speed of the sand mill is 2500r / min. The milling time is 5h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0052] (3) Graphene was mixed in methanol solution and then sand milled. The liquid-solid ratio of graphene to methanol was 60:1 mL:g. The speed of the sand mill was 2400 r / min and the sand milling time was 4 h.

[0053] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1000 r / min and the time is 1.5 h to make the silicon and graphene mix evenly. The second sand milling speed is 2200 r / min and the time is 1.5 h to make the silicon and graphene initially bond. The third sand milling speed is 2800 r / min and the time is 1 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 65%.

[0054] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 15% of the silicon-based anode material. The carbon is added in the form of polyvinylpyrrolidone. During the spray drying process, the feed rate is 12 ml / min. The obtained material is then subjected to high-temperature carbonization. The heating rate during the carbonization process is 10℃ / min. The temperature of the high-temperature heat treatment is 1100℃, and the holding time is 1.5h.

[0055] like Figure 3 The figure shown is a comparison of the electrochemical performance of the silicon-based composite material prepared in Example 3 and the ordinary silicon anode material. Figure 3 As can be seen from this, the silicon-based anode material prepared by this invention has better performance.

[0056] Example 4

[0057] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0058] (1) Using silicon recovered from photovoltaic solar panels as raw material, silicon powder was placed in HF-methanol solution and ultrasonically dispersed for 45 min to remove the oxide layer and other impurities on the surface of silicon material. The concentration of HF was 1 mol / L, the concentration of methanol was 1 mol / L, and the liquid-solid ratio of HF-methanol solution system to silicon powder was 60:1 (mL:g). After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0059] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of methanol solution to silicon powder is 80:1 (mL:g). The speed of the sand mill is 2600r / min. The milling time is 4.5h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0060] (3) Graphene was mixed in methanol solution and then sand milled. The liquid-solid ratio of graphene to methanol was 60:1 (mL:g). The speed of the sand mill was 2600r / min and the sand milling time was 4h.

[0061] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1300 r / min and the time is 1.5 h to make the silicon and graphene mix evenly. The second sand milling speed is 2000 r / min and the time is 3 h to make the silicon and graphene initially bond. The third sand milling speed is 2800 r / min and the time is 3 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 70%.

[0062] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 30% of the silicon-based anode material. The carbon is added in the form of polyvinylpyrrolidone. During the spray drying process, the feed rate is 20 ml / min, the spray outlet temperature is 160°C, and the obtained material is subjected to high-temperature carbonization. The heating rate during the carbonization process is 10°C / min, the high-temperature heat treatment temperature is 1300°C, and the holding time is 2 h.

[0063] like Figure 4 The figure shows the long-cycle performance of the silicon-based composite material prepared in Example 4.

[0064] Example 5

[0065] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0066] (1) Using commercially produced silicon powder as raw material, the silicon powder was placed in an HF-ethanol solution and ultrasonically dispersed for 80 min to remove the oxide layer and other impurities on the surface of the silicon material. In the HF-ethanol solution, the HF concentration was 20 mol / L and the ethanol concentration was 0.5 mol / L. The liquid-solid ratio of the HF-ethanol solution system to the silicon powder was 10:1, with the unit being mL:g. After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0067] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 500:1, and the unit is mL:g. The speed of the sand mill is 1000r / min and the milling time is 48h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0068] (3) After mixing graphene in an ethanol solution, the graphene to ethanol liquid-solid ratio is 30:1 (mL:g), the speed of the mill is 1500r / min, and the milling time is 10h.

[0069] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1000 r / min and the time is 1 h to make the nano-silicon and graphene mix evenly. The second sand milling speed is 2000 r / min and the time is 2 h to make the silicon and graphene initially combine. The third sand milling speed is 2700 r / min and the time is 2 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 90%.

[0070] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 50% of the silicon-based anode material. The carbon is added in the form of glucose. During the spray drying process, the feed rate is 200 mL / min, the spray outlet temperature is 200℃, and the obtained material is subjected to high-temperature carbonization. The heating rate during the carbonization process is 30℃ / min, the high-temperature heat treatment temperature is 1500℃, and the holding time is 1h.

[0071] Example 6

[0072] A novel method for preparing a high-performance silicon-based anode material with a composite structure, comprising the following steps:

[0073] (1) Using commercially produced silicon powder as raw material, the silicon powder was placed in an HF-ethanol solution and ultrasonically dispersed for 80 min to remove the oxide layer and other impurities on the surface of the silicon material. In the HF-ethanol solution, the HF concentration was 1 mol / L and the ethanol concentration was 20 mol / L. The liquid-solid ratio of the HF-ethanol solution system to the silicon powder was 200:1, with the unit being mL:g. After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0074] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 10:1, and the unit is mL:g. The speed of the sand mill is 2800r / min and the milling time is 1h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0075] (3) After mixing graphene in an ethanol solution, the graphene to ethanol liquid-solid ratio is 30:1 (mL:g), the speed of the mill is 2800r / min, and the milling time is 1h.

[0076] (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling. The first sand milling speed is 1000 r / min and the time is 1 h to make the nano-silicon and graphene mix evenly. The second sand milling speed is 2000 r / min and the time is 2 h to make the silicon and graphene initially combine. The third sand milling speed is 2700 r / min and the time is 2 h to make the silicon embedded on the graphene surface, and finally form a graphene / silicon with a silicon mass percentage of 90%.

[0077] (5) After adding carbon to the slurry obtained in step (4), spray drying is performed. The amount of carbon added is 10% of the silicon-based anode material. The carbon is added in the form of glucose. During the spray drying process, the feed rate is 200 mL / min, the spray outlet temperature is 200℃, and the obtained material is subjected to high-temperature carbonization. The heating rate during the carbonization process is 30℃ / min, the high-temperature heat treatment temperature is 600℃, and the holding time is 48h.

[0078] Comparative Example 1

[0079] (1) Using commercially produced silicon powder as raw material, the silicon powder was placed in an HF-ethanol solution and ultrasonically stirred for 80 min to remove the oxide layer and other impurities on the surface of the silicon material. The HF concentration was 1 mol / L, the ethanol concentration was 1 mol / L, and the liquid-solid ratio of the HF-ethanol solution system to the silicon powder was 10:1 (mL:g). After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0080] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 100:1 (mL:g). The speed of the sand mill is 2800r / min. The milling time is 3h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0081] (3) After mixing graphene in an ethanol solution, the graphene and ethanol liquid-solid ratio mL:g is 30:1, the speed of the sand mill is 1500r / min, and the sand milling time is 10h.

[0082] (4) Add the slurry containing nano-silicon from step (2) to the graphene obtained in step (3), mix only, do not sand mill, and finally form graphene / silicon with a silicon mass percentage of 70%.

[0083] (5) Add glucose to the slurry obtained in step (4) and spray dry it. Theoretically, the mass fraction of the carbon material after carbonization is 20% after adding glucose. During the spray drying process, the feed rate is 20 mL / min and the spray outlet temperature is 110℃. The obtained material is then subjected to high-temperature carbonization. The heating rate during carbonization is 5℃ / min, the temperature of the high-temperature heat treatment is 900℃, and the holding time is 2h.

[0084] The difference between Comparative Example 1 and Example 1 is that in step (4), nano-silicon and graphene in Example 1 are mixed using a segmented sand milling method, while in Comparative Example 1, they are mixed using a stirring method. Figure 5 The rate performance of the materials synthesized in Example 1 and Comparative Example 1 is shown. It can be found that the segmented sand milling allows silicon to be embedded in graphene, resulting in a composite material with better rate performance.

[0085] Comparative Example 2

[0086] A method for preparing a silicon-based anode material, the specific steps of which are as follows:

[0087] (1) Using commercially produced silicon powder as raw material, the silicon powder was placed in an HF-ethanol solution and ultrasonically stirred for 80 min to remove the oxide layer and other impurities on the surface of the silicon material. The HF concentration was 1 mol / L, the ethanol concentration was 1 mol / L, and the liquid-solid ratio of the HF-ethanol solution system to the silicon powder was 10:1 (mL:g). After solid-liquid separation and stirring, the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0088] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 100:1 (mL:g). The speed of the sand mill is 2800r / min. The milling time is 3h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0089] (3) After mixing graphene in an ethanol solution, the graphene to ethanol liquid-solid ratio is 30:1 (mL:g), the speed of the mill is 1500r / min, and the milling time is 10h.

[0090] (4) Add the slurry containing nano-silicon from step (2) to the graphene obtained in step (3), and perform sand milling (without segmented sand milling, the sand milling speed is 2800 r / min, and the time is 3h) to finally form graphene / silicon with a silicon mass percentage of 70%.

[0091] (5) Add glucose to the slurry obtained in step (4) and spray dry it. Theoretically, the mass fraction of the carbon material after carbonization is 20% after adding glucose. During the spray drying process, the feed rate is 20 mL / min and the spray outlet temperature is 110℃. The obtained material is then subjected to high-temperature carbonization. The heating rate during carbonization is 5℃ / min, the temperature of the high-temperature heat treatment is 900℃, and the holding time is 2h.

[0092] The difference between Comparative Example 2 and Example 1 is that in step (4), nano-silicon and graphene in Example 1 are mixed using a segmented sand milling method, while Comparative Example 2 is mixed using a single-segment sand milling method. Figure 6 The comparison of the cycling performance of the materials synthesized in Example 1 and Comparative Example 2 shows that the segmented sand milling process allows silicon to be embedded in graphene, resulting in a composite material with better cycling performance.

[0093] Comparative Example 3

[0094] A method for preparing a silicon-based anode material, the specific steps of which are as follows:

[0095] (1) Using photovoltaic silicon cutting waste as raw material, silicon powder is placed in HF-ethanol solution and ultrasonically stirred for 100 min to remove the oxide layer and other impurities on the surface of silicon material. The HF concentration is 2 mol / L, the ethanol concentration is 2 mol / L, and the liquid-solid ratio of the HF-ethanol solution system to silicon powder is 20:1 (mL:g). After solid-liquid separation and stirring, the powder is washed with deionized water until the washing liquid is neutral to obtain purified silicon powder.

[0096] (2) The purified silicon powder in step (1) is milled in a sand mill. The liquid-solid ratio of ethanol solution to silicon powder is 40:1 (mL:g). The speed of the sand mill is 2300r / min. The milling time is 6h. After the milling is completed, a slurry containing nano-silicon is obtained.

[0097] (3) Graphene was mixed in an ethanol solution and then milled. The liquid-solid ratio of graphene to ethanol was 40:1 mL:g. The mill speed was 2300 r / min and the milling time was 4 h.

[0098] (4) The graphene obtained in step (3) is added to the slurry containing nano-silicon in step (2) and subjected to segmented sand milling. The first segment of sand milling is at a speed of 1100 r / min for 1 h to make the silicon and graphene mix evenly. The second segment of sand milling is at a speed of 2100 r / min for 2 h to make the silicon and graphene initially bond. The third segment of sand milling is at a speed of 2700 r / min for 2 h to make the silicon embedded on the graphene surface, and finally the graphene / silicon has a silicon mass percentage of 45%.

[0099] (5) After adding carbon to the slurry obtained in step (4), the material is dried by blowing air. The amount of carbon added is 20% of the silicon-based anode material. The carbon is added in the form of glucose. The material is then carbonized at high temperature. The heating rate during carbonization is 6℃ / min, the temperature of the high-temperature heat treatment is 1000℃, and the holding time is 1.5h.

[0100] The difference between Comparative Example 3 and Example 2 is that in step (5), in Example 2, the slurry obtained in step (4) is spray-dried to obtain a loose structure with a dense carbon layer on the outside and graphene sheets with embedded nano-silicon on the inside, forming a "flower-like" graphene / silicon / carbon composite material. In Comparative Example 3, the drying method is blower drying, which does not form a flower-like structure. Figure 7 To compare the cycling performance of the composite materials synthesized in Example 3 and Example 2, it can be found that the flower-shaped graphene / silicon / carbon composite material formed by spray drying has better cycling stability and longer cycle life, confirming the superiority of this structural design.

Claims

1. A method for preparing a composite silicon-based anode material, characterized in that: The specific preparation method includes the following steps: (1) Silicon powder is obtained by drying and crushing silicon raw materials. The silicon powder is placed in HF-alcohol solution for ultrasonic dispersion, solid-liquid separation, and washing of the solid to obtain purified silicon powder. (2) The purified silicon powder obtained in step (1) is stirred evenly in an alcohol solution and then sand-milled to obtain a slurry containing nano-silicon; (3) After stirring the graphene in the alcohol solution until it is uniform, it is then sand-milled; (4) Add the nano-silicon slurry obtained in step (2) to the graphene obtained in step (3) and perform segmented sand milling to obtain graphene / silicon slurry; (5) Add carbon to the graphene / silicon slurry in step (4), spray dry and granulate, and then carbonize the obtained material at high temperature to obtain a composite silicon-based anode material. In step (4), the segmented sand milling can be a three-stage sand milling process, wherein the first stage sand milling conditions are 1000~1300r / min, and the sand milling time is 1~1.5h; the second stage sand milling conditions are 2000~2200r / min, and the sand milling time is 1.5~3h; and the third stage sand milling conditions are 2700~2800r / min, and the sand milling time is 1~3h. In step (5), during the spray drying process, the feed rate is 1~200mL / min and the spray outlet temperature is 80~200℃; during the carbonization process, the heating rate is 2~30℃ / min, the high-temperature heat treatment temperature is 600~1600℃, and the time is 1~24h.

2. The method for preparing the composite structure silicon-based anode material according to claim 1, characterized in that: In step (1), the silicon raw material is one of the following: recycled silicon waste from the photovoltaic industry, recycled silicon from solar photovoltaic modules, industrial silicon, or commercial silicon powder of different purities.

3. The method for preparing the composite silicon-based anode material according to claim 1, characterized in that: In step (1), the liquid-solid ratio of HF-alcohol solution to silicon powder is (10~500):1, with units of mL:g; in the HF-alcohol solution, the HF concentration is 1~20mol / L, the alcohol concentration is 1~20mol / L, and the alcohol is one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol mixed in any proportion.

4. The method for preparing the composite silicon-based anode material according to claim 1, characterized in that: The ultrasonic dispersion time in step (1) is 10~720 min.

5. The method for preparing the composite structure silicon-based anode material according to claim 1, characterized in that: In step (2), the alcohol solution contains one or more of the following alcohols: methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and ethylene alcohol. The liquid-solid ratio of the alcohol solution to the purified silicon powder is (10~500):1, with units of mL:g. The speed of the sand mill is 1000~3000 r / min, and the sand milling time is 1~48 h.

6. The method for preparing the composite silicon-based anode material according to claim 1, characterized in that: In step (3), the alcohol in the alcohol solution is one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and ethylene alcohol. The liquid-solid ratio of the alcohol solution to the graphene powder is (10~500):1, with the unit being mL:g. When sand milling graphene, the rotation speed of the sand mill is 1000~3000 r / min, and the sand milling time is 1~48 h.

7. The method for preparing the composite structure silicon-based anode material according to claim 1, characterized in that: The mass percentage of silicon in the graphene / silicon slurry formed in step (4) is 10% to 90%.

8. The method for preparing the composite structure silicon-based anode material according to claim 1, characterized in that: In step (5), the mass fraction of carbon is 1% to 70% of the silicon-based anode material. The carbon is added in the form of a carbon source, which is one or more of polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, sugar materials, and aromatic compounds.

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