Method for preparing spherical nano silicon material through molten salt electrolysis by taking inert oxide as template and spherical nano silicon material

Abstract

The invention belongs to the technical field of nano silicon material preparation, and provides a method for preparing a spherical nano silicon material through molten salt electrolysis by taking an inert oxide as a template and the spherical nano silicon material. The method comprises the following steps: carrying out ultrasonic pickling on organic silicon fly ash to obtain fly ash powder; the method comprises the following steps: mixing fly ash powder with an inert oxide, carrying out ball milling to obtain a molten salt electrolysis precursor, mixing the molten salt electrolysis precursor with a binder and a pore forming agent, and pressing to obtain a pole piece; and carrying out molten salt electrolysis by taking the pole piece as a cathode to obtain the spherical nano silicon material. The method is easy to operate, low in cost and high in controllability, the inert oxide can be used as a template for growth of a nano silicon material by utilizing the property that the inert oxide can induce growth of silicon molecules, and silicon dioxide is directly electrolyzed into silicon elementary substances through a fused salt electrolysis method; the method not only realizes recycling of the organic silicon fly ash, but also realizes industrial and clean production of the spherical nano silicon material, and has a very wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of nano-silicon material preparation, in particular to a method for preparing spherical nano-silicon material by molten salt electrolysis using an inert oxide as a template and the spherical nano-silicon material. Background Art

[0002] The organosilicon industry chain is divided into four stages: organosilicon raw materials, organosilicon monomers, organosilicon intermediates, and organosilicon deep processing. The organosilicon production process generates a large amount of waste, which, after combustion, forms organosilicon fly ash. Currently, this organosilicon fly ash remains difficult to handle, making its recycling urgent.

[0003] Spherical nanosilicon materials, due to their unique spherical morphology, exhibit outstanding performance advantages and play an important role in multiple fields: as negative electrode materials for lithium-ion batteries, they possess an ultra-high theoretical specific capacity, and their nano-spherical structure effectively shortens the lithium-ion diffusion path and maintains the integrity of the electrode structure; in electronic packaging, their high thermal conductivity and low thermal expansion coefficient make them ideal thermally conductive / insulating fillers; and in additive manufacturing, their excellent flow properties ensure uniform and dense powder distribution during 3D printing, significantly improving printing accuracy. These application benefits stem from the unique physical and processing properties imparted by the spherical morphology, highlighting the importance of developing high-quality spherical nanosilicon preparation technologies.

[0004] Current technologies for preparing spherical nanosilicon materials are primarily physical and chemical. Physical methods include flame spheronization, high-temperature melt spraying, plasma spheronization, and high-temperature calcination spheronization. Chemical methods include vapor deposition, hydrothermal synthesis, sol-gel, precipitation, and microemulsion. However, these methods suffer from common drawbacks: traditional plasma spheronization consumes too much energy and requires complex equipment; flame spheronization requires high temperatures of 2000-3000°C, has strict requirements for the raw materials used, and is prone to introducing other metallic impurities during high-temperature combustion; and laboratory-scale chemical vapor deposition relies on high-purity silane raw materials, resulting in complex processes and the generation of corrosive gases. These technical bottlenecks severely restrict the industrial production of spherical nanosilicon materials.

[0005] In summary, it is of great significance to develop a method that can recycle and utilize organosilicon fly ash while industrially producing spherical nano-silicon materials. Summary of the Invention

[0006] In view of this, the present invention provides a method for preparing spherical nano-silicon materials by molten salt electrolysis using inert oxides as templates and a spherical nano-silicon material, so as to solve the problems that the existing technology is difficult to industrially produce spherical nano-silicon materials and the organosilicon fly ash generated during the organosilicon production process is difficult to handle.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] The present invention provides a method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template, comprising the following steps:

[0009] 1) ultrasonically acid washing the organosilicon fly ash to obtain fly ash powder;

[0010] 2) mixing the fly ash powder with the inert oxide and ball milling to obtain a molten salt electrolysis precursor, mixing the molten salt electrolysis precursor with a binder and a pore-forming agent, and pressing to obtain an electrode;

[0011] 3) Using the electrode obtained in step 2) as a cathode, molten salt electrolysis is performed to obtain spherical nano-silicon material.

[0012] Preferably, the power of the ultrasonic pickling in step 1) is 100-1500W, the temperature is 25-45°C, and the time is 0.5-6h; the pickling agent for the ultrasonic pickling includes one or more of HCl, H2SO4, and HNO3; and the molar concentration of the pickling agent is 1-6mol / L.

[0013] Preferably, in step 2), the mass ratio of the fly ash powder to the inert oxide is 42-175:12-40; the mass ratio of the molten salt electrolysis precursor to the binder and the pore-forming agent is 50-200:12-53:20-110.

[0014] Preferably, in step 2), the inert oxide includes one or more of aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, hafnium oxide, chromium oxide, yttrium oxide and beryllium oxide; the binder includes one or more of polyvinylidene fluoride, polyvinyl acrylate, polyvinyl alcohol, polyimide and polytetrafluoroethylene; and the pore-forming agent includes one or more of ammonium bicarbonate, ammonium carbonate and polystyrene.

[0015] Preferably, the pressing pressure in step 2) is 10 to 30 MPa.

[0016] Preferably, the anode material of the molten salt electrolysis in step 3) includes one of a graphite rod, a carbon fiber rod, a high-purity carbon rod, a glassy carbon rod or a graphite crucible; the molten salt of the molten salt electrolysis includes one or more of CaCl2, NaCl, KCl, MgCl2, LiCl, AlCl3, BaCl2, MnCl2, ZnCl, CuCl, KF, NaF, LiF, Na2SiF6, CaF2, MgF2, FeF2, ZnF2, NiF2, KI, NaBr, and MnBr.

[0017] Preferably, the temperature of the molten salt electrolysis in step 3) is 650-1000° C., the voltage is 1.8-3.4 V, the time is 2-10 h, and the atmosphere is an inert atmosphere.

[0018] The present invention also provides a spherical nano-silicon material prepared by the above method for preparing spherical nano-silicon material by molten salt electrolysis using an inert oxide as a template. The particle size of the spherical nano-silicon material is 0.5 to 3 μm.

[0019] It can be seen from the above technical solution that compared with the prior art, the present invention has the following beneficial effects:

[0020] 1. The present invention performs ultrasonic acid washing on the organosilicon fly ash generated in the organosilicon production process, and the obtained fly ash powder is mixed with an inert oxide as a molten salt electrolysis precursor for molten salt electrolysis to prepare spherical nano-silicon materials. The method cleverly utilizes the property of inert oxides to induce the growth of silicon molecules, making them a template for the growth of nano-silicon materials. At the same time, based on the original organosilicon fly ash molecules that exist in a spherical morphology, due to the surface tension of the organosilicon fly ash, it will spontaneously form spherical droplets and maintain the spherical morphology after solidification. During the electrolysis process, it grows in a direction to generate uniform spherical nano-silicon materials. This method is simple to operate, low in cost, and highly controllable. It can directly electrolyze silicon dioxide into silicon element; it not only realizes the recycling of organosilicon fly ash, but also realizes the industrial production of spherical nano-silicon materials.

[0021] 2. The method of the present invention utilizes organosilicon fly ash as raw material, which has a wide source of raw materials and low cost. There is no need to prepare high-purity silicon or silane gas in advance, which greatly reduces the cost of raw materials and has significant economic potential.

[0022] 3. The method of the present invention cleverly utilizes the characteristics of cathode deoxidation to form silicon and oxygen precipitation at the anode during molten salt electrolysis to directly synthesize spherical nano-silicon particles in one step, thereby realizing the clean production of spherical nano-silicon materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0024] Figure 1 A diagram of an electrolysis device for preparing spherical nano-silicon materials by molten salt electrolysis according to the present invention, wherein: (1) air inlet; (2) air outlet; (3) water inlet; (4) water outlet; (5) heat insulation layer; (6) anode; (7) cathode; (8) separator;

[0025] Figure 2 XRD pattern of the spherical nanosilicon material prepared in Example 1;

[0026] Figure 3 SEM image of the spherical nanosilicon material prepared in Example 1 at 24000 times magnification;

[0027] Figure 4 SEM image of the spherical nanosilicon material prepared in Example 1 at 29000 times magnification. DETAILED DESCRIPTION

[0028] The present application provides a method for preparing a spherical nanosilicon material by molten salt electrolysis with inert oxide as a template, comprising the following steps:

[0029] 1) ultrasonic acid washing organic silicon fly ash to obtain fly ash powder;

[0030] 2) mixing the fly ash powder with inert oxide, ball milling to obtain a molten salt electrolysis precursor, mixing the molten salt electrolysis precursor with a binder and a pore-forming agent, pressing to obtain an electrode sheet;

[0031] 3) molten salt electrolysis with the electrode sheet obtained in step 2) as a cathode to obtain a spherical nanosilicon material.

[0032] In the present application, the power of the ultrasonic acid washing in step 1) is 100-1500 W, preferably 200-800 W, further preferably 200-650 W, and more preferably 250-500 W; the temperature of the ultrasonic acid washing is 25-45℃, preferably 28-42℃, further preferably 30-40℃, and more preferably 32-35℃; the time of the ultrasonic acid washing is 0.5-6 h, preferably 1-5 h, further preferably 2-4 h, and more preferably 3 h; the acid washing agent of the ultrasonic acid washing comprises one or several of HCl, H2SO4 and HNO3; the molar concentration of the acid washing agent is 1-6 mol / L, preferably 1.5-5.5 mol / L, further preferably 2-5 mol / L, and more preferably 3-4 mol / L.

[0033] In the present application, the ultrasonic acid washing in step 1) is further preferably followed by washing and drying; the solvent of the washing is preferably water; the temperature of the drying is preferably 60-70℃, further preferably 62-68℃, and more preferably 65℃; the time of the drying is preferably 1-12 h, further preferably 3-8 h, and more preferably 6-7 h.

[0034] In the present invention, the mass ratio of the fly ash powder to the inert oxide in step 2) is 42-175:12-40, preferably 50-160:15-35, more preferably 60-150:17-30, and more preferably 70-100:20-25; the mass ratio of the molten salt electrolysis precursor to the binder and the pore-forming agent is 50-200:12-53:20-110, preferably 60-180:15-50:35-100, more preferably 80-150:20-45:40-90, and more preferably 100-120:30-35:50-80.

[0035] In the present invention, the inert oxide in step 2) includes one or more of aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, hafnium oxide, chromium oxide, yttrium oxide and beryllium oxide; the inert oxide promotes the electrical deoxidation of silicon dioxide, induces the growth of silicon particles, and promotes the formation of spherical nano-silicon materials during the electrolysis process.

[0036] In the present invention, the binder in step 2) includes one or more of polyvinylidene fluoride, polyvinyl acetate, polyvinyl alcohol, polyimide and polytetrafluoroethylene; the pore-forming agent includes one or more of ammonium bicarbonate, ammonium carbonate and polystyrene.

[0037] In the present invention, the pressing pressure in step 2) is 10 to 30 MPa, preferably 12 to 28 MPa, more preferably 15 to 25 MPa, and even more preferably 18 to 20 MPa.

[0038] In the present invention, the anode material of the molten salt electrolysis in step 3) includes one of a graphite rod, a carbon fiber rod, a high-purity carbon rod, a glassy carbon rod or a graphite crucible; the molten salt of the molten salt electrolysis includes one or more of CaCl2, NaCl, KCl, MgCl2, LiCl, AlCl3, BaCl2, MnCl2, ZnCl, CuCl, KF, NaF, LiF, Na2SiF6, CaF2, MgF2, FeF2, ZnF2, NiF2, KI, NaBr, and MnBr.

[0039] In the present invention, the temperature of the molten salt electrolysis in step 3) is 650-1000°C, preferably 700-950°C, more preferably 750-900°C, and more preferably 800-850°C; the voltage of the molten salt electrolysis is 1.8-3.4V, preferably 1.9-3.0V, more preferably 2.0-2.8V, and more preferably 2.2-2.4V; the time of the molten salt electrolysis is 2-10h, preferably 3-9h, more preferably 4-8h, and more preferably 5-6h; the atmosphere of the molten salt electrolysis is an inert atmosphere; the gas of the inert atmosphere preferably includes one or more of argon, nitrogen and helium.

[0040] In the present invention, the cathode in step 3) preferably further includes an operation of fixing the cathode; the material of the fixed cathode is preferably one of molybdenum wire, molybdenum hook, nickel mesh and zirconium mesh.

[0041] In the present invention, the molten salt electrolysis in step 3) is preferably followed by pickling and drying operations; the pickling solvent is preferably one or more of HCl, H2SO4, HNO3 and HF; the molar concentration of the solvent is preferably 0.5-6 mol / L, more preferably 1-5 mol / L, more preferably 2-4 mol / L; the pickling time is preferably 0.5-4 h, more preferably 1-3 h, more preferably 2-2.5 h; the drying is preferably vacuum drying, and the vacuum drying temperature is preferably 50-80 ° C, more preferably 55-75 ° C, more preferably 60-65 ° C; the vacuum drying time is preferably 4-24 h, more preferably 8-20 h, more preferably 10-15 h.

[0042] In the present invention, the device for molten salt electrolysis in step 3) is preferably Figure 1 The electrolysis device shown is not considered to be a limitation of the present invention; the electrolysis device includes an inner cylinder, an outer cylinder and a cooling device; the inner cylinder is installed at the bottom of the outer cylinder; the cooling device is sleeved on the side surface of the outer cylinder; an anode (6) and a cathode (7) are provided in the inner cylinder; the partitions (8) are preferably three, which are installed in sequence above the inner cylinder to fix the anode and cathode and the protective electrode; the heat insulation layer (5) is provided on the side surface of the outer cylinder and is located below the cooling device to reduce heat loss, stabilize the electrolysis temperature and protect the equipment structure; the side surface of the outer cylinder is also provided with an air inlet (1) and an air outlet (2) for introducing inert gas into the inner cylinder; the side surface of the cooling device is provided with a water inlet (3) and a water outlet (4) for circulating cooling water to cool the outer cylinder.

[0043] The present invention also provides a spherical nano-silicon material prepared by the above-mentioned method of preparing spherical nano-silicon material by molten salt electrolysis using an inert oxide as a template. The particle size of the spherical nano-silicon material is 0.5 to 3 μm, preferably 0.6 to 2 μm, further preferably 0.8 to 1.5 μm, and more preferably 1 to 1.2 μm.

[0044] The technical solutions provided by the present invention are 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.

[0045] Example 1

[0046] 1) placing the organosilicon fly ash in a 4 mol / L hydrochloric acid solution and ultrasonically pickling the solution at a power of 500 W and a temperature of 25° C. for 2 h, washing the solution with deionized water, and then vacuum drying the solution at a temperature of 70° C. for 6 h to obtain a fly ash powder;

[0047] 2) 7 g of fly ash powder was mixed with 2 g of alumina and ball-milled to obtain a molten salt electrolysis precursor. The molten salt electrolysis precursor was mixed with polyvinyl alcohol and ammonium bicarbonate in a mass ratio of 90:21:45, and pressed under a pressure of 15 MPa to obtain an electrode;

[0048] 3) Use Figure 1 The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is wrapped with molybdenum wire as the cathode, a graphite rod is used as the anode, and a mixed molten salt of NaCl and CaCl2 is used as the molten salt system, wherein the mass of CaCl2 is 210g and the mass of NaCl is 105g. At the same time, 10g of NaF is added to the above molten salt system to prevent silicon particles from agglomerating. Then, the mixture is heated at a heating rate of 5°C / min in an argon atmosphere with a gas flow rate of 20mL / min, and is kept warm for 80m after being heated to 500°C. in to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation is completed, the temperature is increased at a rate of 2°C / min. After heating to 800°C, the molten salt electrolysis is started. At the same time, the voltage of the molten salt electrolysis is controlled to 2.2V. The electrolysis product obtained after 6 hours of molten salt electrolysis is pickled with HCl with a molar concentration of 4 mol / L for 30 minutes under magnetic stirring, then washed with deionized water, and then vacuum dried at 60°C for 12 hours to obtain spherical nano-silicon materials with a particle size of 0.5 to 2 μm.

[0049] The XRD pattern of the spherical nano-silicon material prepared in Example 1 is as follows Figure 2 As shown, from Figure 2 It can be seen that there are obvious silicon peaks in the standard characteristic peaks of silicon at 28.4°, 47.3°, 56.12° and 69.13°, and the half-peak width is large, indicating that the spherical silicon grains are small;

[0050] The SEM image of the spherical nano-silicon material prepared in Example 1 is as follows Figures 3-4 As shown, Figure 3 This is a SEM image at 24,000 times magnification. Figure 4 This is the SEM image when it is magnified 29000 times. Figures 3-4 It can be seen that by adding inert oxide as a template, silicon ions can obtain electrons on the cathode surface during the electrolysis process. The surface tension will promote the gradual aggregation of these atoms to form a spherical structure, and finally spherical particles will be deposited on the cathode.

[0051] Example 2

[0052] 1) placing the organosilicon fly ash in a 4 mol / L hydrochloric acid solution and ultrasonically pickling the solution at a power of 500 W and a temperature of 25° C. for 1.5 h, washing the solution with deionized water, and then vacuum drying the solution at a temperature of 60° C. for 12 h to obtain a fly ash powder;

[0053] 2) 10 g of fly ash powder was mixed with 3 g of zirconium oxide and ball-milled to obtain a molten salt electrolysis precursor, which was then mixed with polyvinyl alcohol and ammonium carbonate in a mass ratio of 125:25:54 and pressed under a pressure of 20 MPa to obtain an electrode;

[0054] 3) Use Figure 1 The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is hung on a molybdenum hook as a cathode, a graphite rod is used as an anode, and a mixed molten salt of NaCl, KCl and MgCl2 is used as a molten salt system in a zirconia crucible, wherein the mass of NaCl is 120g, the mass of KCl is 60g, and the mass of MgCl2 is 60g. At the same time, 12g of CaF2 is added to the above molten salt system to prevent silicon particles from agglomerating. Then, the mixture is heated at a heating rate of 3°C / min in an argon atmosphere with a gas flow rate of 15mL / min to 5 After heating to 850°C, the molten salt was electrolyzed for 100 minutes to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation was completed, the molten salt was heated at a heating rate of 3°C / min. After heating to 850°C, the molten salt electrolysis was started. At the same time, the voltage of the molten salt electrolysis was controlled to 2.4V. The electrolysis product obtained after 10 hours of molten salt electrolysis was pickled with H2SO4 with a molar concentration of 2 mol / L under magnetic stirring for 1 hour, then washed with deionized water, and then vacuum dried at 60°C for 10 hours to obtain spherical nano-silicon materials with a particle size of 1 to 2.5 μm.

[0055] Example 3

[0056] 1) placing the organosilicon fly ash in a 4 mol / L hydrochloric acid solution and ultrasonically pickling the solution at a power of 800 W and a temperature of 30° C. for 1 hour, washing the solution with deionized water, and then vacuum drying the solution at a temperature of 60° C. for 6 hours to obtain a fly ash powder;

[0057] 2) 9 g of fly ash powder was mixed with 1.5 g of beryllium oxide and ball-milled to obtain a molten salt electrolysis precursor. The molten salt electrolysis precursor was mixed with polyvinylidene fluoride and ammonium bicarbonate in a mass ratio of 52:26:35, and pressed under a pressure of 12 MPa to obtain an electrode;

[0058] 3) Use Figure 1The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is wrapped with molybdenum wire as the cathode, and a graphite rod is used as the anode. A mixed molten salt of KF, NaF and LiF is used as the molten salt system in an alumina crucible, wherein each of KF, NaF and LiF is 100g. At the same time, 20g of NaCl is added to the above molten salt system to lower the melting point of the fluoride molten salt system, and then heated at a heating rate of 2°C / min in a nitrogen atmosphere with a gas flow rate of 20mL / min, heated to 600°C and kept warm for 12 0min to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation is completed, the temperature is increased at a rate of 5℃ / min. After heating to 900℃, molten salt electrolysis is started. At the same time, the voltage of molten salt electrolysis is controlled at 2.6V. The electrolysis product obtained after molten salt electrolysis for 4h is pickled with HNO3 with a molar concentration of 4mol / L for 1h under magnetic stirring, then washed with deionized water, and then vacuum dried at 60℃ for 24h to obtain spherical nano-silicon material with a particle size of 1 to 2.4μm.

[0059] Example 4

[0060] 1) placing the organosilicon fly ash in a 4 mol / L hydrochloric acid solution and ultrasonically pickling the solution at a power of 1000 W and a temperature of 40° C. for 0.5 h, washing the solution with deionized water, and then vacuum drying the solution at a temperature of 60° C. for 6 h to obtain a fly ash powder;

[0061] 2) 8.5 g of fly ash powder was mixed with 2.2 g of chromium oxide and ball-milled to obtain a molten salt electrolysis precursor. The molten salt electrolysis precursor was mixed with polyvinyl alcohol and ammonium bicarbonate in a mass ratio of 70:20:52, and pressed under a pressure of 25 MPa to obtain an electrode;

[0062] 3) Use Figure 1The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is wrapped with molybdenum wire as the cathode, a graphite crucible is used as the anode, and a mixed molten salt of KF and NaF is used as the molten salt system, wherein the mass of KF and NaF is 150g respectively. At the same time, 18g of Na2SiF6 is added to the above molten salt system to form a protective layer and reduce the van der Waals force attraction between the particles, thereby inhibiting agglomeration. Then, the mixture is heated at a heating rate of 5°C / min to 600°C in a nitrogen atmosphere with a gas flow rate of 10mL / min. The mixture was then kept warm for 120 minutes to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation was completed, the mixture was heated at a heating rate of 5°C / min. After heating to 950°C, molten salt electrolysis was started. At the same time, the voltage of the molten salt electrolysis was controlled to 2.4V. The electrolysis product obtained after 7 hours of molten salt electrolysis was pickled with HCl with a molar concentration of 2 mol / L for 30 minutes under magnetic stirring, then washed with deionized water, and then vacuum dried at 60°C for 18 hours to obtain spherical nano-silicon material with a particle size of 1 to 2 μm.

[0063] Example 5

[0064] 1) placing the organosilicon fly ash in a 6 mol / L sulfuric acid solution and ultrasonically pickling the solution at a power of 1000 W and a temperature of 40° C. for 0.5 h, washing the solution with deionized water, and then vacuum drying the solution at a temperature of 60° C. for 6 h to obtain a fly ash powder;

[0065] 2) 12 g of fly ash powder was mixed with 3 g of yttrium oxide and ball-milled to obtain a molten salt electrolysis precursor, which was then mixed with polyvinylidene fluoride and ammonium bicarbonate in a mass ratio of 120:21:70, and pressed under a pressure of 12 MPa to obtain an electrode;

[0066] 3) Use Figure 1The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is wrapped with a nickel mesh as a cathode, a graphite crucible is used as an anode, and a mixed molten salt of KF, NaF and MgF2 is used as a molten salt system, wherein the mass of KF is 150g, the mass of NaF and MgF2 is 75g respectively, and 25g of KCl is added to the above molten salt system to lower the melting point of the fluoride molten salt system, and then heated at a heating rate of 3°C / min in an argon atmosphere with a gas flow rate of 20mL / min, heated to 500°C and kept warm for 150 min to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation is completed, the temperature is increased at a rate of 5°C / min. After heating to 1000°C, the molten salt electrolysis is started. At the same time, the voltage of the molten salt electrolysis is controlled at 2.6V. The electrolysis product obtained after 6 hours of molten salt electrolysis is pickled with HCl and HF with a molar concentration of 4 mol / L for 30 minutes under magnetic stirring, and then washed with deionized water. It is then vacuum dried at 80°C for 4 hours to obtain spherical nano-silicon materials with a particle size of 1.2 to 2.1 μm.

[0067] Example 6

[0068] 1) placing the organosilicon fly ash in a 2 mol / L mixed acid solution of hydrochloric acid and sulfuric acid (the mass ratio of hydrochloric acid to sulfuric acid is 1:1), and ultrasonically pickling the solution at a power of 800 W and a temperature of 45° C. for 2 h. After ultrasonic pickling, washing the solution with deionized water was performed, and then vacuum drying was performed at a temperature of 65° C. for 6 h to obtain fly ash powder.

[0069] 2) 9 g of fly ash powder was mixed with 1.7 g of hafnium oxide and ball-milled to obtain a molten salt electrolysis precursor. The molten salt electrolysis precursor was mixed with polyvinyl alcohol and ammonium carbonate in a mass ratio of 150:34:67, and pressed under a pressure of 23 MPa to obtain an electrode.

[0070] 3) Use Figure 1The electrolysis device shown in the figure is prepared, and the electrode obtained in step 2) is wrapped with a nickel mesh as a cathode, a graphite rod is used as an anode, and a mixed molten salt of KF, NaF and ZnF2 is used as a molten salt system, wherein the mass of KF is 100g, the mass of NaF and ZnF2 is 50g respectively, and 10g of KCl is added to the above molten salt system to lower the melting point of the fluoride molten salt system, and then heated at a heating rate of 3°C / min in an argon atmosphere with a gas flow rate of 16mL / min, and kept warm after heating to 500°C. The molten salt was heated for 120 minutes to remove moisture from the molten salt and reduce side reactions during molten salt electrolysis. After the insulation was completed, the temperature was increased at a rate of 5°C / min. After heating to 900°C, the molten salt electrolysis was started. At the same time, the voltage of the molten salt electrolysis was controlled to 2.6V. The electrolysis product obtained after 10 hours of molten salt electrolysis was pickled with HCl with a molar concentration of 2 mol / L for 2 hours under magnetic stirring, and then washed with deionized water. It was then vacuum dried at 80°C for 12 hours to obtain spherical nano-silicon materials with a particle size of 0.5 to 1.6 μm.

[0071] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template, characterized in that: The steps include: 1) ultrasonically acid washing the organosilicon fly ash to obtain fly ash powder; 2) mixing the fly ash powder with the inert oxide and ball milling to obtain a molten salt electrolysis precursor, mixing the molten salt electrolysis precursor with a binder and a pore-forming agent, and pressing to obtain an electrode; 3) Using the electrode obtained in step 2) as a cathode, molten salt electrolysis is performed to obtain spherical nano-silicon material.

2. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to claim 1, characterized in that: The ultrasonic pickling in step 1) is performed at a power of 100 to 1500 W, a temperature of 25 to 45° C., and a time of 0.5 to 6 h; The pickling agent for ultrasonic pickling includes one or more of HCl, H2SO4, and HNO3; the molar concentration of the pickling agent is 1 to 6 mol / L.

3. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to claim 2, characterized in that: The mass ratio of the fly ash powder to the inert oxide in step 2) is 42-175:12-40; The mass ratio of the molten salt electrolysis precursor to the binder and the pore-forming agent is 50-200:12-53:20-110.

4. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to any one of claims 1 to 3, characterized in that: The inert oxide in step 2) includes one or more of aluminum oxide, zirconium oxide, titanium oxide, zinc oxide, hafnium oxide, chromium oxide, yttrium oxide and beryllium oxide; The binder includes one or more of polyvinylidene fluoride, polyvinyl acrylate, polyvinyl alcohol, polyimide and polytetrafluoroethylene; The pore-forming agent includes one or more of ammonium bicarbonate, ammonium carbonate and polystyrene.

5. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to claim 4, characterized in that: The pressing pressure in step 2) is 10-30 MPa.

6. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to claim 5, characterized in that: The anode material for the molten salt electrolysis in step 3) comprises one of a graphite rod, a carbon fiber rod, a high-purity carbon rod, a glassy carbon rod or a graphite crucible; The molten salt for molten salt electrolysis includes one or more of CaCl2, NaCl, KCl, MgCl2, LiCl, AlCl3, BaCl2, MnCl2, ZnCl, CuCl, KF, NaF, LiF, Na2SiF6, CaF2, MgF2, FeF2, ZnF2, NiF2, KI, NaBr, and MnBr.

7. The method for preparing spherical nano-silicon materials by molten salt electrolysis using an inert oxide as a template according to claim 6, characterized in that: The temperature of the molten salt electrolysis in step 3) is 650-1000° C., the voltage is 1.8-3.4 V, the time is 2-10 h, and the atmosphere is an inert atmosphere.

8. The spherical nano-silicon material prepared by the method for preparing spherical nano-silicon material by molten salt electrolysis using an inert oxide as a template according to any one of claims 1 to 7, characterized in that: The particle size of the spherical nano-silicon material is 0.5-3 μm.

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