Differential feeding device for preparing novel silicon monoxide negative electrode material and preparation method
By combining a differential feeding device and a dust collector, the problem of uneven mixing of silicon suboxide anode material was solved, improving the electrochemical performance and production efficiency of the battery, and achieving more efficient material blending and product quality.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-03
AI Technical Summary
In current lithium battery production, uneven mixing of silicon suboxide anode materials leads to a decline in electrochemical performance, affecting the battery's initial coulombic efficiency, reversible capacity, and cycle performance.
A differential feeding device is adopted, with fluorides and metal compounds stored separately in the first and second buffer bins. The first and second feeding motors control the proportional differential feeding, so that silicon suboxide, fluorides and metal compounds are uniformly mixed in the high-speed mixer. Combined with the dust collector for rapid dust removal, the uniform mixing of materials is achieved.
It improves the uniformity of material mixing, enhances the electrochemical performance of the novel silicon-oxygen anode material, and strengthens the battery's initial coulombic efficiency, reversible capacity, and cycle performance. At the same time, it improves production efficiency and reduces the pollution risk caused by manual feeding.
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Figure CN121775702A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of battery material preparation technology, specifically relating to a differential feeding device and preparation method for preparing novel silicon suboxide anode materials. Background Technology
[0002] Lithium-ion batteries have gradually become the mainstream of chemical energy storage due to their high energy density and long cycle life. In recent years, with the development of electric vehicles, the demand for lithium battery products has been growing at a rate of over 30%, while also placing higher demands on their capacity, safety, fast charging, and cycle life. Currently, the anode materials for lithium batteries on the market are mainly carbon-based materials represented by graphite, and the capacity of mainstream products is approaching their theoretical capacity. Developing new lithium battery anode materials has become crucial. Silicon (Si) anode materials have a theoretical specific capacity of 4200 mAh / g, but they experience significant volume changes (>300%) during charge and discharge, leading to material breakage, rapid capacity decay, and safety hazards. Anode materials made by carbon-coating silicon suboxide offer high capacity, small expansion volume, high initial charge-discharge coulombic efficiency, and longer cycle life, making them an important development direction for high-energy silicon-based anode materials.
[0003] However, during the initial charge-discharge process, silicon suboxide forms electrochemically inert substances such as lithium silicate and lithium oxide, which leads to a low initial coulombic efficiency. Therefore, adding fluorides and specific metal compounds to the surface of silicon suboxide can effectively improve the electrochemical performance of the product through interface effects and structural regulation.
[0004] Currently, production plants use manual, layered feeding to achieve material mixing. In practical applications, multiple powders are fed simultaneously. Due to differences in particle size and degree of agglomeration, some materials agglomerate or are unevenly distributed after manual feeding during the mixing process. This results in uneven mixing in the VC machine or high-speed mixer, reducing the electrochemical performance of the product. Summary of the Invention
[0005] To address the shortcomings of existing technologies, this invention provides a differential feeding device and preparation method for preparing novel silicon suboxide anode materials. This invention comprehensively improves production efficiency and the electrochemical performance of the product. This invention ultimately solves the problem of uneven material mixing caused by existing feeding processes, which leads to a decrease in product performance. This invention is beneficial for improving the initial coulombic efficiency, reversible capacity, and cycle performance of batteries.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: A differential feeding device for preparing a novel silicon suboxide anode material includes a first buffer chamber and a second buffer chamber. The first buffer chamber is fixedly connected to the side wall of a first feed pipe, and the second buffer chamber is fixedly connected to the side wall of a second feed pipe. The first feed pipe and the second feed pipe are respectively fixedly connected to both ends of a feed tee pipe, and the other ends of the first feed pipe and the second feed pipe are respectively fixedly connected to a first feeding motor and a second feeding motor. The third end of the feed tee is fixedly connected to the intermediate tank, and the bottom of the intermediate tank is fixedly connected to the feed inlet of the high-speed mixer.
[0007] Furthermore, an electronic valve is installed on the feed inlet; a drive motor is fixedly installed on the base of the high-speed mixer, and a first pulley is fixedly connected to the output end of the drive motor; a rotating shaft is rotatably connected to the bottom of the high-speed mixer, and a second pulley is fixedly connected to one end of the rotating shaft, which is connected to the first pulley via belt drive; a stirring paddle is fixedly connected to the other end of the rotating shaft, and the stirring paddle is located inside the high-speed mixer.
[0008] Furthermore, a discharge tee pipe is fixedly connected to one side of the bottom of the high-speed mixer. A dust collector is fixedly installed at one end of the discharge tee pipe, and the other end is connected to the feed pipe of the mixing tank. One end of the dust collector is fixedly connected to the top of the mixing tank.
[0009] Furthermore, another dust collector is fixedly connected to the top of the high-speed mixer.
[0010] Furthermore, the first and second buffer bins are fixedly installed on the feeding platform.
[0011] This invention also claims a method for preparing novel silicon suboxide anode materials using the differential feeding device described above, comprising the following steps: Step 1: Use a mixer to mix silicon suboxide powder, fluoride and metal compound using differential feeding to obtain a mixture; Step 2: Place the mixture into an organic carbon source for mixing, coating, and calcination; Step 3: The sintered material obtained in Step 2 is pulverized using airflow to obtain a novel silicon-oxygen anode material.
[0012] Furthermore, in step 1, silicon suboxide is located within the high-speed mixer 500, while fluorides and metal compounds are located in the first buffer chamber 100 and the second buffer chamber 200, respectively.
[0013] Further, the silicon suboxide powder mentioned in step 1 has a size D50 of 5-6 μm, the fluoride includes one or more of NaF, CaF2, Na2SiF6, and NH4F, and the metal compound includes one or more of LiNO3, LiCl, Li2CO3, LiOH, Li3PO4, MgNO3, MgCl2, MgCO3, and Mg(OH)2; the mass ratio of silicon suboxide to fluoride and metal compound is 50:1-4:1-4.
[0014] Further, the organic carbon source mentioned in step 2 is one or more of asphalt, polyvinylpyrrolidone, glucose, sucrose, and phenolic resin; the sintering process is as follows: the temperature is raised from room temperature to 300-600℃ at a heating rate of 1-5℃ / min, held for 2-5 hours, and then raised to 750-950℃ at a heating rate of 2-10℃ / min, held for 3-6 hours.
[0015] Furthermore, the airflow pulverizing pressure in step 3 is 0.2-0.35 MPa.
[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) In this invention, fluorides and metal compounds are placed separately in the first buffer bin and the second buffer bin, respectively. Then, the first feeding motor and the second feeding motor feed the materials at a set ratio differential speed, so that the fluorides and metal compounds of different ratios are uniformly mixed in the intermediate tank and enter the high-speed mixer to mix with silicon suboxide. The differential feeding method effectively improves the uniformity of material mixing, which greatly improves the electrochemical performance of the new silicon-oxygen anode material. At the same time, the dust collector is connected to the discharge three-way pipe and the mixing tank simultaneously, which can also quickly and effectively remove dust and ensure product quality. Finally, the production efficiency and the electrochemical performance of the product are comprehensively improved by differential feeding + synchronous dust removal.
[0017] (2) This invention uses a differential feeding method to uniformly divide silicon suboxide, fluoride, and metal compound into N equal parts within 10 minutes through different screws or spraying equipment in a ratio of 50:1:1, 50:2:2, or 50:3:3, during a continuous feeding process. Simultaneously, each part is uniformly mixed. This effectively improves the uniformity of material mixing, increases production efficiency, reduces the risk of contamination caused by manual feeding, and ultimately solves the problem of uneven material mixing in existing feeding processes, which leads to decreased product performance.
[0018] (3) The novel silicon-oxygen anode material of the present invention is a composite material obtained by uniformly mixing silicon suboxide, fluoride, and metal compound as raw materials through differential feeding and then sintering. The inorganic matter generated by the reaction is difficult to amorphize during charging and discharging, and will not undergo a reversible reaction to generate active SiO2 during charging and discharging. Furthermore, due to its irreversibility, it can also act as a buffer layer to suppress the volume expansion of SiOx anode material, which is beneficial to improving the initial coulombic efficiency, reversible capacity, and cycle performance of the battery. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the overall structure of a differential feeding device for preparing novel silicon suboxide anode materials according to the present invention. Figure 2 This is a partial structural schematic diagram of a differential feeding device for preparing novel silicon suboxide anode materials according to the present invention.
[0020] The attached figures are labeled as follows: First buffer bin-100, first feeding motor-110, first feed pipe-120, second buffer bin-200, second feeding motor-210, second feed pipe-220, feed tee-300, intermediate tank-400, high-speed mixer-500, feed inlet-510, electronic valve-511, drive motor-520, first pulley-521, second pulley-530, rotating shaft-540, stirring paddle-550, discharge tee-560, dust collector-600, mixing tank-700, feeding platform-800. Detailed Implementation
[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Of course, the specific embodiments described herein are merely illustrative and not intended to limit the invention.
[0022] Although the steps in this invention are arranged by reference numerals, this is not intended to limit the order of the steps. Unless the order of the steps is explicitly stated or the execution of a step requires other steps as a basis, the relative order of the steps can be adjusted. It is understood that the term "and / or" as used herein refers to and covers any and all possible combinations of one or more of the associated listed items.
[0023] Example 1 like Figures 1-2As shown, a differential feeding device for preparing a novel silicon suboxide anode material includes a first buffer chamber 100 and a second buffer chamber 200. The first buffer chamber 100 is fixedly connected to the side wall of a first feed pipe 120, and the second buffer chamber 200 is fixedly connected to the side wall of a second feed pipe 220. The first feed pipe 120 and the second feed pipe 220 are respectively fixedly connected to both ends of a feed tee pipe 300, and the other ends of the first feed pipe 120 and the second feed pipe 220 are respectively fixedly connected to a first feed motor 110 and a second feed motor 210. The third end of the feed tee 300 is fixedly connected to the intermediate tank 400, and the bottom of the intermediate tank 400 is fixedly connected to the feed inlet 510 of the high-speed mixer 500.
[0024] Furthermore, an electronic valve 511 is installed on the feed inlet 510; a drive motor 520 is fixedly installed on the base of the high-speed mixer 500, and a first pulley 521 is fixedly connected to the output end of the drive motor 520; a rotating shaft 540 is rotatably connected to the bottom of the high-speed mixer 500, and a second pulley 530 is fixedly connected to one end of the rotating shaft 540, and the second pulley 530 and the first pulley 521 are connected by belt drive; a stirring paddle 550 is fixedly connected to the other end of the rotating shaft 540, and the stirring paddle 550 is located inside the high-speed mixer 500.
[0025] Furthermore, a discharge tee pipe 560 is fixedly connected to one side of the bottom of the high-speed mixer 500. One end of the discharge tee pipe 560 is fixedly connected to a dust collector 600, and the other end is connected to the feed pipe of the mixing tank 700. One end of the dust collector 600 is fixedly connected to the top of the mixing tank 700.
[0026] This invention uses a first buffer chamber 100 and a second buffer chamber 200 to separately place fluorides and metal compounds, respectively. Then, the first feeding motor 110 and the second feeding motor 210 feed the materials at a set ratio and differential speed, so that the fluorides and metal compounds in different proportions are uniformly mixed in the intermediate tank 400 and then mixed with silicon suboxide in the high-speed mixer 500. The differential feeding method effectively improves the uniformity of material mixing, which greatly enhances the electrochemical performance of the prepared novel silicon-oxygen anode material. At the same time, the dust collector 600 is connected to the discharge three-way pipe 560 and the mixing tank 700 simultaneously, which can quickly and effectively remove dust and ensure product quality. Finally, the differential feeding + synchronous dust removal method comprehensively improves production efficiency and product electrochemical performance.
[0027] Furthermore, another dust collector 600 is fixedly connected to the top of the high-speed mixer 500.
[0028] Furthermore, the first buffer bin 100 and the second buffer bin 200 are fixedly installed on the feeding platform 800.
[0029] A method for preparing novel silicon suboxide anode materials using the differential feeding device described above includes the following steps: Step 1: Use a mixer to mix silicon suboxide powder, fluoride and metal compound using differential feeding to obtain a mixture; Step 2: Place the mixture into an organic carbon source for mixing, coating, and calcination; Step 3: The sintered material obtained in Step 2 is pulverized using airflow to obtain a novel silicon-oxygen anode material.
[0030] This invention utilizes a differential feeding method to uniformly divide silicon suboxide, fluoride, and metal compounds into N equal portions within 10 minutes using different screws or spray nozzles, in ratios of 50:1:1, 50:2:2, or 50:3:3, through continuous feeding. Simultaneously, each portion is uniformly mixed. This effectively improves the uniformity of material mixing, increases production efficiency, reduces the risk of contamination from manual feeding, and ultimately solves the problem of uneven material mixing and subsequent product performance degradation caused by existing feeding processes.
[0031] Furthermore, in step 1, silicon suboxide is located within the high-speed mixer 500, while fluorides and metal compounds are located in the first buffer chamber 100 and the second buffer chamber 200, respectively.
[0032] Further, the silicon suboxide powder mentioned in step 1 has a size D50 of 5-6 μm, the fluoride includes one or more of NaF, CaF2, Na2SiF6, and NH4F, and the metal compound includes one or more of LiNO3, LiCl, Li2CO3, LiOH, Li3PO4, MgNO3, MgCl2, MgCO3, and Mg(OH)2; the mass ratio of silicon suboxide to fluoride and metal compound is 50:1-4:1-4.
[0033] Further, the organic carbon source mentioned in step 2 is one or more of asphalt, polyvinylpyrrolidone, glucose, sucrose, and phenolic resin; the sintering process is as follows: the temperature is raised from room temperature to 300-600℃ at a heating rate of 1-5℃ / min, held for 2-5 hours, and then raised to 750-950℃ at a heating rate of 2-10℃ / min, held for 3-6 hours.
[0034] Furthermore, the airflow pulverizing pressure in step 3 is 0.2-0.35 MPa.
[0035] Example 2 1) Preparation of the mixture: First, weigh 110 kg of silicon suboxide powder, 2.2 kg of fluoride, and 2.2 kg of metal compound. Mix silicon suboxide, NaF, and LiF in a 50:1:1 ratio at a differential speed of 11 kg of silicon suboxide, 0.22 kg of fluoride, and 0.22 kg of metal compound per minute to obtain a brown mixture.
[0036] 2) After coating the material obtained in step 1) with the organic carbon source, the temperature is increased from room temperature to 300℃ at a rate of 5℃ / min and held for 2 hours. Then, the temperature is increased to 750℃ at a rate of 10℃ / min and held for 3 hours. The organic carbon source is asphalt.
[0037] 3) The sintered material obtained in step 2) is subjected to airflow pulverization at a pressure of 0.2 MPa to obtain a novel silicon-oxygen anode material.
[0038] The novel silicon-oxygen anode material of this invention is a composite material obtained by uniformly mixing silicon suboxide, fluorides, and metal compounds as raw materials through a differential feeding method, followed by a sintering reaction. The inorganic substances generated in the reaction are difficult to amorphize during charge and discharge, and will not undergo a reversible reaction to generate active SiO2. Furthermore, due to its irreversibility, it can also act as a buffer layer to suppress the volume expansion of the SiOx anode material, which is beneficial to improving the battery's initial coulombic efficiency, reversible capacity, and cycle performance.
[0039] Example 3 1) Preparation of the mixture: First, weigh 110 kg of silica powder, 4.4 kg of fluoride, and 4.4 kg of metal compound. Mix silica, CaF2, and LiCl in a 50:2:2 ratio at a differential speed of 11 kg silica, 0.44 kg fluoride, and 0.44 kg metal compound per minute, resulting in a brown mixture.
[0040] 2) After coating the material obtained in step 1) with the organic carbon source, the temperature was increased from room temperature to 350℃ at a rate of 5℃ / min and held for 2.5h, then increased to 780℃ at a rate of 10℃ / min and held for 3.5h. The organic carbon source was glucose.
[0041] 3) The sintered material obtained in step 2) is subjected to airflow pulverization at a pressure of 0.25 MPa to obtain a novel silicon-oxygen anode material.
[0042] Example 4 1) Preparation of the mixture: First, weigh out 110 kg of silica powder, 6.6 kg of fluoride, and 6.6 kg of metal compound. Mix silica powder, Na2SiF6, and MgCO3 in a 50:3:3 ratio at a differential speed of 11 kg of silica powder, 0.66 kg of fluoride, and 0.66 kg of metal compound per minute to obtain a brown mixture.
[0043] 2) After coating the material obtained in step 1) with the organic carbon source, the temperature is increased from room temperature to 400℃ at a rate of 5℃ / min and held for 3 hours, then increased to 810℃ at a rate of 10℃ / min and held for 4 hours. The organic carbon source is phenolic resin.
[0044] 3) The sintered material obtained in step 2) is subjected to airflow pulverization at a pressure of 0.3 MPa to obtain a novel silicon-oxygen anode material.
[0045] Example 5 1) Preparation of the mixture: First, weigh 110 kg (8.8 kg) of silica powder and 8.8 kg of metal compound. Mix silica, NH4F, and MgCl2 in a 50:4:4 ratio at a differential speed of 11 kg silica, 0.88 kg fluoride, and 0.88 kg metal compound per minute to obtain a brown mixture.
[0046] 2) After coating the material obtained in step 1) with the organic carbon source, the temperature is increased from room temperature to 450℃ at a heating rate of 5℃ / min and held for 3.5h, then increased to 840℃ at a heating rate of 10℃ / min and held for 4.5h. The organic carbon source is polyvinylpyrrolidone.
[0047] 3) The sintered material obtained in step 2) is subjected to airflow pulverization at a pressure of 0.35 MPa to obtain a novel silicon-oxygen anode material.
[0048] Comparative Example 1 110 kg of silicon suboxide powder (D50 5-6 μm) was weighed and mixed with NaF and LiF in a 50:1:1 ratio by manual feeding. The mixture was then directly coated with asphalt and heated from room temperature to 300°C at a rate of 5°C / min, held at that temperature for 2 hours, and then heated to 750°C at a rate of 10°C / min, held at that temperature for 3 hours. The sintered material was then subjected to airflow pulverization at a pressure of 0.2 MPa to obtain a novel silicon-oxygen anode material.
[0049] This application involves testing a novel silicon-oxygen anode material fabricated into a lithium-ion battery, specifically: The lithium-ion battery includes a positive electrode, a negative electrode, a separator, an electrolyte, etc., and its assembly sequence from negative electrode to positive electrode is as follows: positive electrode shell, positive electrode, electrolyte, separator, electrolyte, negative electrode, gasket, negative electrode shell, and then they are pressed together.
[0050] Preparation of the negative electrode sheet: The novel silicon-oxygen negative electrode material, conductive agent, and binder are mixed in a ratio of 8:1:1. After thorough grinding with the addition of solvent, the mixture is coated onto copper foil and dried in an oven. After drying, it is cut into 12mm diameter round sheets and stored in a glove box for later use.
[0051] The positive electrode is a lithium sheet.
[0052] The conductive agent is one of acetylene black, conductive carbon black, conductive graphite, carbon nanotubes, graphene, etc.
[0053] The binder is one of sodium carboxymethyl cellulose, sodium alginate, and polyvinylidene fluoride. Sodium carboxymethyl cellulose is preferred.
[0054] The drying temperature is 60~120℃, and the drying time is 1~20h.
[0055] The electrolyte is EC / DEC = 1:110%FEC1%VC.
[0056] Battery testing: Battery testing is mainly conducted on the Blue Electric testing software at a test temperature of 30℃.
[0057] Battery tests were conducted using the examples and comparative examples, and the data are shown in Table a: Table a. Comparison of data for button-type lithium-ion batteries
[0058] As demonstrated by the assembled batteries, the novel silicon-oxygen anode material produced using a differential feeding method significantly improves the performance of lithium-ion batteries. Compared to batteries produced without differential feeding, it noticeably enhances the initial coulombic efficiency and cycle performance, while also greatly increasing production speed. This novel silicon-oxygen anode material is a composite material obtained by uniformly mixing silicon suboxide, fluorides, and metal compounds using a differential feeding method, followed by a sintering reaction. The inorganic substances generated in the reaction are difficult to amorphize during charge and discharge, preventing reversible reactions that could generate active SiO2. Furthermore, due to its irreversibility, it can act as a buffer layer to suppress the volume expansion of the SiOx anode material, thus improving the initial coulombic efficiency, reversible capacity, and cycle performance of the battery.
[0059] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.
Claims
1. A differential feeding device for preparing novel silicon suboxide anode materials, characterized in that, It includes a first buffer chamber (100) and a second buffer chamber (200). The first buffer chamber (100) is fixedly connected to the side wall of the first feed pipe (120), and the second buffer chamber (200) is fixedly connected to the side wall of the second feed pipe (220). The first feed pipe (120) and the second feed pipe (220) are respectively fixedly connected to both ends of the feed tee pipe (300). The other ends of the first feed pipe (120) and the second feed pipe (220) are respectively fixedly connected to the first feed motor (110) and the second feed motor (210). The third end of the feed tee (300) is fixedly connected to the intermediate tank (400), and the bottom of the intermediate tank (400) is fixedly connected to the feed inlet (510) of the high-speed mixer (500).
2. The differential feeding device for preparing novel silicon suboxide anode materials according to claim 1, characterized in that, An electronic valve (511) is installed on the feed inlet (510); a drive motor (520) is fixedly installed on the base of the high-speed mixer (500), and a first pulley (521) is fixedly connected to the output end of the drive motor (520); a rotating shaft (540) is rotatably connected to the bottom of the high-speed mixer (500); a second pulley (530) is fixedly connected to one end of the rotating shaft (540), and the second pulley (530) and the first pulley (521) are connected by belt drive; a stirring paddle (550) is fixedly connected to the other end of the rotating shaft (540), and the stirring paddle (550) is located inside the high-speed mixer (500).
3. The differential feeding device for preparing novel silicon suboxide anode materials according to claim 2, characterized in that, The bottom side of the high-speed mixer (500) is fixedly connected to a discharge tee pipe (560), one end of which is fixedly connected to a dust collector (600), and the other end is connected to the feed pipe of the mixing tank (700); one end of the dust collector (600) is fixedly connected to the top of the mixing tank (700).
4. The differential feeding device for preparing novel silicon suboxide anode materials according to claim 3, characterized in that, Another dust collector (600) is fixedly connected to the top of the high-speed mixer (500).
5. The differential feeding device for preparing novel silicon suboxide anode materials according to claim 1, characterized in that, The first buffer bin (100) and the second buffer bin (200) are fixedly installed on the feeding platform (800).
6. A method for preparing novel silicon suboxide anode materials using the differential feeding apparatus described in any one of claims 1 to 5, characterized in that, Includes the following steps: Step 1: Use a mixer to mix silicon suboxide powder, fluoride and metal compound using differential feeding to obtain a mixture; Step 2: Place the mixture into an organic carbon source for mixing, coating, and calcination; Step 3: The sintered material obtained in Step 2 is pulverized using airflow to obtain a novel silicon-oxygen anode material.
7. The preparation method according to claim 6, characterized in that, In step 1, silicon suboxide is located in the high-speed mixer (500), and fluoride and metal compound are located in the first buffer chamber (100) and the second buffer chamber (200), respectively.
8. The preparation method according to claim 6, characterized in that, The silicon suboxide powder mentioned in step 1 has a size D50 of 5-6 μm, the fluoride includes one or more of NaF, CaF2, Na2SiF6, and NH4F, and the metal compound includes one or more of LiNO3, LiCl, Li2CO3, LiOH, Li3PO4, MgNO3, MgCl2, MgCO3, and Mg(OH)2; the mass ratio of silicon suboxide to fluoride and metal compound is 50:(1~4):(1~4).
9. The preparation method according to claim 6, characterized in that, The organic carbon source mentioned in step 2 is one or more of asphalt, polyvinylpyrrolidone, glucose, sucrose, and phenolic resin; the sintering process is as follows: the temperature is raised from room temperature to 300-600℃ at a heating rate of 1-5℃ / min, held for 2-5h, and then raised to 750-950℃ at a heating rate of 2-10℃ / min, held for 3-6h.
10. The preparation method according to claim 6, characterized in that, The airflow pulverizing pressure in step 3 is 0.2-0.35 MPa.