Silicon-carbon composite negative electrode material, and preparation method and application thereof

Abstract

The application provides a silicon-carbon composite negative electrode material and a preparation method and application thereof, and belongs to the technical field of new energy materials and electrochemistry. Silicon powder and metal oxide are tightly combined through sand milling to build a continuous and stable structure, the volume expansion of the silicon powder and the metal oxide is inhibited, the stress of the silicon powder is released, then the sand-milled composite slurry is mixed with carbon material, and spray drying granulation and carbonization treatment are performed to prepare the negative electrode material. Based on the mutual stability effect, the application can accommodate and relieve the large volume expansion of the silicon material, and the stability of the material is maintained. The prepared composite negative electrode shows extremely low volume expansion (<20%). The metal oxide in the application has the ability to stabilize the SEI film and improve the conductivity. In combination with the addition of the carbon material, the conductivity of the composite material is synergistically improved, and the electrochemical performance is improved. Therefore, the prepared composite material has high sphericity, high tap density and excellent electrochemical performance.

Description

Technical Field

[0001] This invention relates to the fields of new energy materials and electrochemical technology, and in particular to a silicon-carbon composite anode material, its preparation method, and its application. Background Technology

[0002] Benefiting from the booming development of consumer markets such as electronics and new energy vehicles, the market size and technological level of lithium batteries and anode materials have continued to improve. Currently, carbon-based materials, represented by artificial graphite, are the main materials used in lithium-ion battery anodes, accounting for 95% of the market share. At present, commercially available graphite anode materials are approaching their theoretical specific capacity limit (372 mAh / g). To further improve battery energy density, finding anode materials with higher specific capacity has become a key focus of industry research. Due to its outstanding performance advantages, silicon-based anode materials have become one of the recognized mainstream technologies in the lithium-ion battery industry. Promoting technological breakthroughs and commercialization of silicon-based anode materials, and breaking through the performance limits of graphite anode materials, is of great significance for improving lithium battery performance and supporting the development of downstream application markets.

[0003] However, silicon materials struggle to meet current commercial demands due to their low conductivity and significant volume expansion. Therefore, developing a simple strategy to effectively address the issues of large volume expansion and poor conductivity faced by silicon-based anodes is crucial for their widespread application. Summary of the Invention

[0004] The purpose of this invention is to provide a silicon-carbon composite anode material, its preparation method, and its application. The method is simple and efficient, and can effectively solve the problems of large volume expansion and poor conductivity faced by silicon-based anodes.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:

[0007] Silicon powder, metal oxide and alcohol solution are mixed and then milled to obtain a composite slurry;

[0008] The composite slurry is mixed with carbon material and spray-dried to obtain granules;

[0009] The granular material is carbonized to obtain a silicon-carbon composite anode material.

[0010] The metal oxides include one or more of titanium monoxide, titanium dioxide, aluminum oxide, zinc oxide, iron tetroxide, ferric oxide, copper oxide, cuprous oxide, tin oxide, manganese oxide, vanadium oxide, calcium oxide, and silver oxide.

[0011] Preferably, the mass ratio of silicon powder to metal oxide in the mixture of silicon powder and metal oxide is 10-90%.

[0012] Preferably, the alcohol in the alcohol solution includes one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol, the volume fraction of the alcohol solution is 5-90%, and the volume ratio of the alcohol solution to the total mass of silicon powder and metal oxide is (10-1000) mL:1g.

[0013] Preferably, the rotation speed of the sand mill used in the sand mill is 1000-3000 r / min, and the sand milling time is 1-48 h.

[0014] Preferably, the carbon material includes one or more of carbon nanotubes, graphite, pitch, graphene, pyrolytic carbon source and biomass carbon source, and the theoretical mass fraction of carbon formed after carbonization treatment in the silicon-carbon composite anode material is 1-70%.

[0015] Preferably, the pyrolysis carbon source includes one or more of polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, saccharides, and aromatic compounds.

[0016] Preferably, the spray drying conditions include: a feed rate of 0.1 to 200 mL / min and a spray outlet temperature of 80 to 200°C.

[0017] Preferably, the carbonization treatment temperature is 600–1600°C, the time is 0.5–24 h, and the heating rate to the carbonization treatment temperature is 1–30°C / min.

[0018] The present invention provides a silicon-carbon composite anode material prepared by the preparation method described in the above technical solution.

[0019] This invention provides the application of the silicon-carbon composite anode material described in the above technical solution in lithium-ion batteries.

[0020] This invention provides a method for preparing a silicon-carbon composite anode material. Silicon powder and metal oxides are combined using a sand milling method to form an embedded, continuous, and stable structure. Since silicon exhibits a large volume expansion rate during charge-discharge cycles, while metal oxides have a small volume expansion rate, and some metal oxides do not even participate in the charge-discharge reaction and therefore do not experience volume expansion, the lower volume expansion rate of the metal oxides helps suppress the volume expansion of silicon and release its stress. Based on the "mutual stabilization effect," this invention can accommodate and mitigate the large volume expansion of silicon materials, maintaining material stability. The prepared Si / MxOy / C composite anode exhibits extremely low volume expansion (<20%), solving the problem of volume expansion and contraction during charge-discharge processes leading to the failure of silicon-based composite materials.

[0021] The metal oxides added in this invention possess high electrical conductivity. When combined with silicon powder particles, they form conductive channels, enabling more efficient electron transport during charging and discharging. Furthermore, the electron conduction pathways formed between the metal oxide particles and silicon powder particles enhance the electron conductivity of the silicon material, thereby reducing resistance loss and improving energy conversion efficiency. Moreover, the metal oxides stabilize the SEI film, allowing for a more robust SEI film to be formed in the composite anode material constructed through sand milling. The carbon material added in this invention further improves the conductivity of the composite material, resulting in a silicon-based composite material with high sphericity, uniform particle size, and high tap density during spray drying granulation. Therefore, the metal oxides in this invention have the ability to stabilize the SEI film and improve conductivity. Combined with the addition of carbon materials, they synergistically enhance the conductivity of the composite material, improving electrochemical performance. Consequently, the prepared composite material exhibits high sphericity, high tap density, and excellent electrochemical performance.

[0022] The method of this invention is simple and efficient, and can effectively solve the problems of large volume expansion and poor conductivity faced by silicon-based anodes. The process flow is short and has a kilogram-level production capacity, which has broad application prospects.

[0023] The raw materials for the silicon powder used in this invention can be widely selected. Commercial silicon powder of different particle sizes can be used, or recycled silicon waste from diamond wire cutting in the photovoltaic industry and silicon recovered from solar photovoltaic modules can be used as raw material sources to reduce the cost of material preparation. Attached Figure Description

[0024] Figure 1 The XRD comparison diagram (a) and SEM diagram (b) of the silicon waste (SCW), TiO2, Si / TiO2 mixture and silicon-carbon composite anode material Si / TiO2 / C in Example 1 are shown.

[0025] Figure 2The images show the SEM image (ac) and elemental analysis diagram (df) of the cross-section of the Si / TiO2 / C silicon-carbon composite anode material in Example 1.

[0026] Figure 3 SEM image of the silicon-carbon composite material prepared in Example 2;

[0027] Figure 4 The rate performance diagram shows the silicon raw material and the prepared silicon-carbon composite anode material (Si / Al2O3 / C) in Example 3.

[0028] Figure 5 This is a particle size distribution diagram of the silicon-carbon composite anode material in Example 4;

[0029] Figure 6 Here is a SEM image of the composite anode material in Comparative Example 1;

[0030] Figure 7 This is a comparison graph showing the cycle performance of silicon waste and the synthesized material S-Si in Comparative Example 2 with the silicon-carbon composite anode material Si / TiO2 / C in Example 1. Detailed Implementation

[0031] This invention provides a method for preparing a silicon-carbon composite anode material, comprising the following steps:

[0032] Silicon powder, metal oxide and alcohol solution are mixed and then milled to obtain a composite slurry;

[0033] The composite slurry is mixed with carbon material and spray-dried to obtain granules;

[0034] The granular material is carbonized to obtain a silicon-carbon composite anode material.

[0035] The metal oxides include one or more of titanium monoxide, titanium dioxide, aluminum oxide, zinc oxide, iron tetroxide, ferric oxide, copper oxide, cuprous oxide, tin oxide, manganese oxide, vanadium oxide, calcium oxide, and silver oxide.

[0036] In this invention, unless otherwise specified, all raw materials required for preparation are commercially available products well known to those skilled in the art.

[0037] This invention involves mixing silicon powder, metal oxide, and alcohol solution, followed by sand milling to obtain a composite slurry.

[0038] In this invention, the silicon powder is preferably purified silicon powder; the preparation method of the purified silicon powder preferably includes: drying and crushing the silicon material in sequence, placing the obtained silicon material in an HF-alcohol solution for ultrasonic dispersion under stirring conditions, separating the solid and liquid, washing the obtained solid with water until the washing liquid is neutral, and obtaining purified silicon powder; this invention removes the oxide layer and other impurities on the surface of the silicon material by ultrasound.

[0039] In this invention, the silicon material is preferably recycled silicon waste from diamond wire cutting in the photovoltaic industry, silicon recycled from solar photovoltaic modules, industrial silicon, or commercial silicon powder of different purities.

[0040] In this invention, the HF concentration in the HF-alcohol solution is preferably 0.1–20 mol / L, more preferably 0.8–10 mol / L, further preferably 1–2 mol / L, and even more preferably 1.5 mol / L; the alcohol concentration is preferably 0.1–20 mol / L, more preferably 1.0–3 mol / L, and even more preferably 1.2–1.8 mol / L; the alcohol is preferably one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol; the liquid-solid ratio of the HF-alcohol solution to the silicon material is preferably (10–1000) mL:1 g, more preferably (20–500) mL:1 g, and even more preferably (100–150) mL:1 g; the ultrasonic dispersion time is preferably 10–720 min, more preferably 80–300 min, and even more preferably 120–240 min.

[0041] The present invention does not impose any special limitations on the solid-liquid separation and water washing process, and can be carried out in accordance with the process known in the art.

[0042] In this invention, the metal oxide preferably includes one or more of the following: titanium monoxide (TiO), titanium dioxide (TiO2), aluminum oxide (Al2O3), zinc oxide (ZnO), iron(II,III) oxide (Fe3O4), ferric oxide (Fe2O3), copper oxide (CuO), cuprous oxide (Cu2O), tin oxide (SnO2), manganese oxide (MnO2), vanadium oxide (V2O3), calcium oxide (CaO), and silver oxide (Ag2O). When the metal oxide is two or more of the above, this invention does not have a special limitation on the ratio of different types of metal oxides, and can be adjusted according to actual needs.

[0043] In this invention, the mass ratio of silicon powder in the mixture of silicon powder and metal oxide is preferably 10-90%, more preferably 40-80%, and even more preferably 60-70%.

[0044] In this invention, the alcohols in the alcohol solution preferably include one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol. When the alcohols are two or more of the above, this invention does not have a special limitation on the ratio of different types of alcohols, and any ratio is acceptable. The volume concentration of the alcohol solution is preferably 5-90%, more preferably 15-85%, and even more preferably 50-80%. The volume ratio of the alcohol solution to the total mass of silicon powder and metal oxide is preferably (10-1000) mL:1g, more preferably (35-500) mL:1g, and even more preferably (50-200) mL:1g.

[0045] In this invention, the rotational speed of the sand mill used for sand milling is preferably 1000–3000 r / min, more preferably 1800–2800 r / min, and even more preferably 2000–2300 r / min. The sand milling time is preferably 1–48 h, more preferably 5–20 h, and even more preferably 8–12 h. This invention achieves an embedded bonding of silicon and metal oxide through sand milling, while simultaneously forming a uniform slurry, which is beneficial for the subsequent spray drying process.

[0046] After obtaining the composite slurry, the present invention mixes the composite slurry with carbon material and spray-dries it to obtain granules.

[0047] In this invention, the carbon material preferably includes one or more of carbon nanotubes, graphite, pitch, graphene, pyrolytic carbon source, and biomass carbon source, more preferably carbon nanotubes and pyrolytic carbon source; when the carbon material is two or more of the above, this invention does not have a special limitation on the ratio of different types of carbon materials, and can be adjusted according to actual needs; the theoretical mass fraction of carbon formed after carbonization treatment in the silicon-carbon composite anode material is 1-70%, more preferably 30-60%, and even more preferably 40-50%.

[0048] When the carbon material is composed of carbon nanotubes and pyrolytic carbon source, during the spray drying step, the carbon nanotubes will be evenly distributed throughout the entire composite material (inside the sphere), constructing a 3D conductive network and improving electronic conductivity. The addition of the pyrolytic carbon source can form a carbon coating on the entire composite material, further stabilizing the composite material and improving the cycle stability of the composite material.

[0049] In this invention, the pyrolysis carbon source preferably includes one or more of polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, sugar materials, and aromatic compounds; the sugar material is preferably glucose or sucrose, and the aromatic compound is preferably aniline or salicylic acid.

[0050] In this invention, the biomass carbon source is preferably wood, straw, or waste; the waste is preferably banana peel or grapefruit peel.

[0051] The present invention does not impose any special limitations on the mixing process of the composite slurry and carbon material; the mixture can be stirred and mixed evenly according to a process known in the art.

[0052] In this invention, the spray drying conditions preferably include: a feed rate of 0.1 to 200 mL / min, more preferably 5 to 150 mL / min, and even more preferably 10 to 20 mL / min; and a spray outlet temperature of 80 to 200°C, more preferably 120 to 180°C, and even more preferably 130 to 150°C.

[0053] After obtaining the granular material, the present invention performs carbonization treatment on the granular material to obtain silicon-carbon composite anode material.

[0054] In this invention, the carbonization treatment is preferably carried out in a tube furnace; the temperature of the carbonization treatment is preferably 600-1600℃, more preferably 800-1300℃, even more preferably 900-1000℃, the time is preferably 0.5-24h, more preferably 2-12h, even more preferably 3-6h, and the heating rate to the carbonization treatment temperature is preferably 1-30℃ / min, more preferably 5-20℃ / min, even more preferably 10-15℃ / min.

[0055] This invention provides a silicon-carbon composite anode material prepared by the preparation method described above. In the silicon-carbon composite anode material prepared by this invention, metal oxides and silicon powder are combined to form small particles. These small particles and carbon materials form a dense, large spherical material under spray drying. The carbon formed during the carbonization process coats the entire large sphere.

[0056] This invention provides the application of the silicon-carbon composite anode material described in the above-mentioned technical solution in lithium-ion batteries. This invention does not specifically limit the method of application; any method well-known in the art can be used.

[0057] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0058] Example 1

[0059] (1) Using silicon waste from photovoltaic cutting as silicon material, the silicon material was dried and crushed, and then placed in an HF-ethanol solution for ultrasonic stirring for 80 min. The HF concentration in the HF-ethanol solution was 1 mol / L, the ethanol concentration was 1 mol / L, and the liquid-solid ratio of the HF-ethanol solution to the silicon material was 10 mL: 1 g. After stirring, the solid and liquid were separated, and the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0060] (2) The purified silicon powder and TiO2 in step (1) are added to an ethanol solution and mixed evenly. The volume fraction of the ethanol solution is 90%, the mass ratio of silicon powder in the Si / TiO2 mixture is 60%, the mass fraction of TiO2 is 40%, and the liquid-solid ratio of ethanol solution to Si / TiO2 is 100mL:1g. The resulting mixture is then milled. The milling speed is 2800r / min and the milling time is 5h. After milling, a composite slurry containing Si / TiO2 is obtained.

[0061] (3) Add carbon nanotubes, PVP and asphalt to the composite slurry containing Si / TiO2 in step (2). The theoretical carbon obtained after carbonization of PVP, asphalt and carbon nanotubes accounts for 40% of the total mass of the composite material (the mass percentage of carbon produced after carbonization of PVP, asphalt and carbon nanotubes is 25%:25%:50%). After stirring evenly, spray dry and granulate. The feed rate is 5mL / min and the spray outlet temperature is 150℃ to obtain granules.

[0062] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 5℃ / min, the treatment temperature is 1000℃, and the holding time is 2h to obtain silicon-carbon composite anode material, denoted as Si / TiO2 / C.

[0063] Example 2

[0064] (1) Using silicon material recovered from photovoltaic solar panels as raw material, the silicon material is dried and crushed, and then placed in HF-propanol solution for ultrasonic stirring for 120 min. The concentration of HF is 0.8 mol / L, the concentration of propanol is 1 mol / L, and the liquid-solid ratio of HF-ethanol solution to silicon material is 20 mL: 1 g. After stirring, solid and liquid are separated, and the powder is washed with deionized water until the washing liquid is neutral to obtain purified silicon powder.

[0065] (2) The purified silicon powder and Fe2O3 from step (1) are added to a propanol solution with a volume fraction of 80% and mixed evenly. The mass ratio of silicon powder in the Si / Fe2O3 mixture is 80%, the mass fraction of Fe2O3 is 20%, and the liquid-solid ratio of propanol solution to Si / Fe2O3 is 50mL:1g. The resulting mixture is then milled in a sand mill at a speed of 2000r / min for 8h to obtain a composite slurry containing Si / Fe2O3.

[0066] (3) Add glucose and PVP to the composite slurry containing Si / Fe2O3 in step (2). The theoretical carbon obtained after carbonization of glucose and PVP accounts for 30% of the mass of the composite material (the mass percentage of carbon produced after carbonization of glucose and PVP is 50%:50%). After stirring evenly, spray dry and granulate. The feed rate is 10mL / min and the spray outlet temperature is 130℃ to obtain granules.

[0067] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 10℃ / min, the treatment temperature is 900℃, and the holding time is 3h to obtain silicon-carbon composite anode material.

[0068] Example 3

[0069] (1) Using commercial silicon powder as silicon material, the silicon material was placed in an HF-ethanol solution and ultrasonically stirred for 300 min. The HF concentration was 1 mol / L, the ethanol concentration was 1.2 mol / L, and the liquid-solid ratio of the HF-propanol solution to the silicon material was 30 mL: 1 g. After stirring, the solid and liquid were separated, and the powder was washed with deionized water until the washing solution was neutral to obtain purified silicon powder.

[0070] (2) The purified silicon powder and Al2O3 from step (1) are added to an ethanol solution with a volume fraction of 85% and mixed evenly. The mass ratio of silicon in the Si / Al2O3 mixture is 70%, and the liquid-solid ratio of propanol solution to Si / Al2O3 is 10mL:1g. The resulting mixture is then milled in a sand mill at a speed of 1800r / min for 12h to obtain a composite slurry containing Si / Al2O3.

[0071] (3) Add asphalt to the composite slurry containing Si / Al2O3 in step (2). The carbon obtained after asphalt carbonization is theoretically 30% of the mass of the composite material. After stirring evenly, spray dry and granulate. The feeding rate is 15mL / min and the spray outlet temperature is 180℃ to obtain granules.

[0072] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 15℃ / min, the treatment temperature is 800℃, and the holding time is 6h to obtain silicon-carbon composite anode material.

[0073] Example 4

[0074] (1) Using commercial silicon powder as silicon material, the silicon material was placed in an HF-butanol solution and ultrasonically stirred for 240 min. The HF concentration was 1.5 mol / L, the butanol concentration was 1.8 mol / L, and the liquid-solid ratio of the HF-butanol solution to the silicon material was 150 mL: 1 g. After stirring, the solid and liquid were separated, and the powder was washed with deionized water until the washing solution was neutral to obtain purified silicon powder.

[0075] (2) The purified silicon powder and CuO in step (1) are added to an ethanol solution with a volume fraction of 80% and mixed evenly. The mass ratio of silicon powder in the Si / CuO mixture is 40%, and the liquid-solid ratio of ethanol solution to Si / CuO is 200mL:1g. The resulting mixture is then milled in a sand mill at a speed of 2300r / min for 10h to obtain a composite slurry containing Si / CuO.

[0076] (3) Add sucrose and phenolic resin to the composite slurry containing Si / CuO in step (2). The theoretical carbon obtained after carbonization of sucrose and phenolic resin accounts for 20% of the mass of the composite material (the mass percentage of carbon produced after carbonization of sucrose and phenolic resin is 30%:70%). After stirring evenly, spray dry and granulate. The feed rate is 5 mL / min and the spray outlet temperature is 120℃ to obtain granules.

[0077] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 10℃ / min, the treatment temperature is 1300℃, and the holding time is 1h to obtain silicon-carbon composite anode material.

[0078] Example 5

[0079] (1) Using commercial silicon powder as silicon material, the silicon material was placed in HF-propanol solution and ultrasonically stirred for 120 min. The HF concentration was 2 mol / L, the butanol concentration was 3 mol / L, and the liquid-solid ratio of HF-butanol solution to silicon material was 100 mL: 1 g. After stirring, solid and liquid were separated, and the powder was washed with deionized water until the washing solution was neutral to obtain purified silicon powder.

[0080] (2) The purified silicon powder and V2O3 in step (1) are added to an ethanol solution with a volume fraction of 75% and mixed evenly. The mass ratio of silicon powder in the Si / V2O3 mixture is 45%, and the liquid-solid ratio of ethanol solution to Si / V2O3 is 35mL:1g. The resulting mixture is then milled in a sand mill at a speed of 1300r / min for 20h to obtain a composite slurry containing Si / V2O3.

[0081] (3) Add asphalt, PVP and sucrose to the composite slurry containing Si / V2O3 in step (2). The theoretical carbon obtained after carbonization of asphalt, PVP and sucrose accounts for 50% of the mass of the composite material (the mass percentage of carbon produced after carbonization of the three materials is 25%:25%:50%). After stirring evenly, spray dry and granulate. The feed rate is 20mL / min and the spray outlet temperature is 160℃ to obtain granules.

[0082] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 20℃ / min, the treatment temperature is 1000℃, and the holding time is 3h to obtain silicon-carbon composite anode material.

[0083] Comparative Example 1

[0084] (1) Using silicon waste from photovoltaic cutting as silicon material, the silicon material was placed in an HF-ethanol solution and ultrasonically stirred for 80 min. The HF concentration in the HF-ethanol solution was 1 mol / L, the ethanol concentration was 1 mol / L, and the liquid-solid ratio of the HF-ethanol solution to the silicon material was 10 mL: 1 g. After stirring, the solid and liquid were separated, and the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0085] (2) The purified silicon powder and TiO2 in step (1) are added to an ethanol solution and mixed evenly. The volume fraction of ethanol is 90%, the mass ratio of silicon powder in the Si / TiO2 mixture is 60%, the mass fraction of TiO2 is 40%, and the liquid-solid ratio of ethanol solution to Si / TiO2 is 100mL:1g, to obtain a composite slurry containing Si / TiO2.

[0086] (3) Add carbon nanotubes, PVP and asphalt to the composite slurry containing Si / TiO2 in step (2). The theoretical carbon obtained after carbonization of PVP, asphalt and carbon nanotubes accounts for 40% of the mass of the composite material (the mass percentage of carbon produced after carbonization of PVP, asphalt and carbon nanotubes is 25%:25%:50%). After stirring evenly, spray dry and granulate. The feed rate is 5mL / min and the spray outlet temperature is 150℃ to obtain granules.

[0087] (4) The granular material in step (3) is subjected to high temperature treatment in a tube furnace. The heating rate is 5℃ / min, the treatment temperature is 1000℃, and the holding time is 2h to obtain silicon-carbon composite anode material, denoted as Si / TiO2 / C-1.

[0088] Comparative Example 2

[0089] (1) Using silicon waste from photovoltaic cutting as silicon material, the silicon material was placed in an HF-ethanol solution and ultrasonically stirred for 80 min. The HF concentration in the HF-ethanol solution was 1 mol / L, the ethanol concentration was 1 mol / L, and the liquid-solid ratio of the HF-ethanol solution to the silicon material was 10 mL: 1 g. After stirring, the solid and liquid were separated, and the powder was washed with deionized water until the washing liquid was neutral to obtain purified silicon powder.

[0090] (2) Add the purified silicon powder from step (1) to the ethanol solution and mix evenly. The volume fraction of ethanol is 90%. The resulting mixture is then milled. The milling speed is 2800 r / min and the milling time is 5 h. After milling, a composite slurry containing milled silicon is obtained.

[0091] (3) Spray dry the slurry containing silicon after sand milling in step (2) to granulate it. The feed rate is 5 mL / min and the spray outlet temperature is 150℃ to obtain granules, which are denoted as S-Si.

[0092] Characterization and performance testing

[0093] (1) Figure 1 The images show a comparison of XRD patterns (a) and SEM images (b) of slicing silicon waste (SCW), TiO2, Si / TiO2 mixture, and silicon-carbon composite anode material Si / TiO2 / C in Example 1.

[0094] In (a), it can be observed that the XRD diffraction peaks of both Si and TiO2 are broadened, indicating that the particle size of both is significantly reduced under the sand milling process. Furthermore, no other impurity peaks were observed, suggesting that the silicon powder and titanium dioxide did not react. In (b), it can be observed that the synthesized composite material exhibits a high degree of sphericity.

[0095] (2) Figure 2 The images show the SEM image (ac) and elemental analysis diagram (df) of the cross-section of the Si / TiO2 / C silicon-carbon composite anode material in Example 1. Figure 2 It can be seen that the Si / TiO2 composite material has a uniform distribution of CN and Ts. The corresponding elemental distribution shows that silicon and titanium are uniformly distributed, indicating that silicon and titanium dioxide are firmly bonded together, which can suppress the volume expansion of silicon. The carbon element forms a coating on the composite material, which helps to improve the cycle stability of the composite material.

[0096] (3) Figure 3 The SEM image of the silicon-carbon composite material prepared in Example 2 shows that the resulting composite material has high sphericity and good uniformity.

[0097] (4) Figure 4This is a rate performance graph of the silicon raw material (commercial silicon powder) and the prepared silicon-carbon composite anode material (Si / Al2O3 / C) in Example 3; (The graph is derived from...) Figure 4 It is known that the Si / Al2O3 / C composite material has excellent rate performance, which is due to the robust structure built based on the "mutual stabilization" effect, which makes the synthesized composite material highly stable and does not have significant capacity decay even under high current.

[0098] 4) Figure 5 This is a particle size distribution diagram of the silicon-carbon composite anode material in Example 4, from... Figure 5 It can be seen that the synthesized composite material D 50 =14um, with uniform particle size distribution.

[0099] 5) Figure 6 The image shows the SEM image of the composite anode material Si / TiO2 / C-1 in Comparative Example 1. Compared with Example 1, Comparative Example 1 only did not undergo the sand milling step, and the other experimental conditions were the same. Comparative Example 1 is simply a metal oxide doping, and the composite material synthesized by spray drying without sand milling has uneven particle size distribution, low sphericity, irregular shape, and low tap density.

[0100] 6) Figure 7 The graph shows a comparison of the cycling performance of silicon waste in Comparative Example 2 and the synthesized material S-Si with the silicon-carbon composite anode material Si / TiO2 / C in Example 1. It can be seen that Si / TiO2 / C has the best cycling stability, and this effect cannot be achieved by simply reducing the particle size of silicon.

[0101] 7) Using the testing equipment of Yuaneng Technology Co., Ltd.: RSS1400, with NCM523 positive electrode material, the silicon-carbon composite negative electrode materials prepared in Examples 1, 2, and 3 were used as negative electrodes. Commercial electrolyte was used: (1.0M LiTFSI, DOL:DME = 1:1 (volume ratio), 2.0% LiNO3 (Vol%)). The volume expansion of the negative electrode materials during charge-discharge cycles was detected at a current of 1A / g. The results showed that after 100 cycles, the volume expansion of the silicon-carbon composite negative electrode material prepared in Example 1 was 15%; the volume expansion of the silicon-carbon composite negative electrode material prepared in Example 2 was 19%; and the volume expansion of the silicon-carbon composite negative electrode material prepared in Example 3 was 17%. That is, the volume expansion of the silicon-carbon composite negative electrode materials prepared in Examples 1 to 3 was less than 20%.

[0102] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a silicon-carbon composite anode material, characterized in that, The steps are as follows: Silicon powder, metal oxide and alcohol solution are mixed and then milled to obtain a composite slurry; The composite slurry is mixed with carbon material and spray-dried to obtain granules; The granular material is carbonized to obtain a silicon-carbon composite anode material. The metal oxide includes one or more of titanium dioxide, aluminum oxide, copper oxide, and vanadium oxide; The mass ratio of silicon powder in the mixture of silicon powder and metal oxide is 10-90%. The speed of the sand mill used in the sand mill is 1000~3000 r / min, and the sand milling time is 1~48 h; The conditions for spray drying include: a feed rate of 0.1~200 mL / min and a spray outlet temperature of 80~200℃.

2. The preparation method according to claim 1, characterized in that, The alcohol in the alcohol solution includes one or more of methanol, ethanol, propanol, butanol, ethylene glycol, propylene glycol, allyl alcohol, and vinyl alcohol. The volume fraction of the alcohol solution is 5-90%, and the volume ratio of the alcohol solution to the total mass of silicon powder and metal oxide is (10-1000) mL:1g.

3. The preparation method according to claim 1, characterized in that, The carbon material includes one or more of carbon nanotubes, graphite, pitch, graphene, pyrolytic carbon source and biomass carbon source, and the theoretical mass fraction of carbon formed after carbonization treatment in silicon-carbon composite anode material is 1~70%.

4. The preparation method according to claim 3, characterized in that, The pyrolysis carbon source includes one or more of polydopamine, resorcinol-formaldehyde resin, polyvinylpyrrolidone, sugar materials, and aromatic compounds.

5. The preparation method according to claim 1, characterized in that, The carbonization treatment is carried out at a temperature of 600~1600℃ for a time of 0.5~24h, and the heating rate to the carbonization treatment temperature is 1~30℃ / min.

6. The silicon-carbon composite anode material prepared by the preparation method according to any one of claims 1 to 5.

7. The application of the silicon-carbon composite anode material according to claim 6 in lithium-ion batteries.

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