Preparation method of sodium ion battery hard carbon material

Abstract

The application relates to a preparation method of a sodium ion battery negative electrode material, comprising the following steps: (S1) uniformly mixing pitch-like substances in the presence of a sulfur compound to obtain mixed precursor I; (S2) pressing the mixed precursor into a sheet, heat-treating the sheet in an oxidizing atmosphere, cooling, and uniformly mixing the crosslinked modified pitch, a pore-forming agent and a pore channel modifier to obtain mixed precursor II; (S3) calcining the mixed precursor II in an inert atmosphere or a hydrocarbon atmosphere, cooling, grinding, acid washing, washing, drying and obtaining an amorphous sodium ion battery negative electrode material. The negative electrode material obtained by the preparation method has high capacity and high energy density, a low cost, a simple preparation process, adjustable disorder degree, high carbon yield and is suitable for large-scale production, and is applied to a sodium ion secondary battery as a negative electrode material.

Description

Technical Field

[0001] This invention relates to the field of materials technology, and in particular to a method for preparing a hard carbon material for sodium-ion batteries. Background Technology

[0002] Secondary batteries, as the primary chemical energy storage device, play a crucial role in this field. Replacing fossil fuels with electricity as the main energy source for transportation will significantly reduce greenhouse gas emissions. Improving various power grid systems by integrating them with renewable energy sources such as wind, solar, and geothermal energy will greatly enhance the efficiency of renewable energy utilization. Sodium-ion batteries, with their advantages of abundant, widely distributed, and low-cost sodium resources, have overcome the limitations of lithium-ion batteries, such as scarce resources, uneven distribution, and high costs, and have received widespread attention and extensive research in recent years. Developing high-performance electrode materials is crucial for the commercialization of sodium-ion batteries. To date, the development of some cathode materials has largely met application requirements, but anode materials still constrain the practical application of sodium-ion batteries.

[0003] Among the reported sodium-ion battery anode materials, amorphous carbon materials have become the most promising anode materials due to their relatively low sodium storage potential, high sodium storage capacity, and good cycle stability. Fossil mineral precursors have significant advantages in the preparation of amorphous carbon materials, as they are inexpensive, have huge domestic reserves, and offer high carbonization yields, possessing strong commercial potential. However, the amorphous carbon materials obtained after calcination have high structural order and low porosity, which reduces the capacity in the low-voltage region, leading to a decrease in the overall battery energy density.

[0004] Taking pitch-based carbon materials as an example, during pitch pyrolysis, the main component, asphaltenes, polymerizes and rearranges into sheet-like aromatic fused ring structures, which then stack into sheets under van der Waals forces. Further heating increases the order and density of the carbon material, eventually transforming it into highly ordered graphite, which is unfavorable for sodium ion storage. We propose using crosslinking copolymers and pore-forming compounds as additives. Inorganic copolymer small molecules can interact with pitch, polymerizing with pitch to produce orthogonally oriented mesophase carbon, inhibiting the ordered rearrangement of carbon layers during calcination of pitch-based precursors. Preferably, pore-forming agents generate more porous structures, and further modification of the pore structure enhances the capacity in the low-pressure plateau region, promoting its large-scale application as a negative electrode in sodium-ion batteries. Summary of the Invention

[0005] To address the issue that the electrochemical performance of existing asphalt-based hard carbon anode materials cannot meet the demands of industrial batteries, this invention provides a sodium-ion battery anode material, its preparation method, and its application. It utilizes abundant and inexpensive fossil industrial waste products such as coal tar pitch, petroleum pitch, and mesophase pitch as raw materials. Sulfur-containing inorganic substances, including persulfates, thiosulfates, sulfur, and sulfide (polysulfide) salts, are used. The process involves heat treatment in an oxidizing atmosphere followed by cross-linking and polymerization of asphaltene to inhibit the polymerization and rearrangement of asphaltene, forming a layered mesophase pitch. Furthermore, alkali metal and alkaline earth metal oxides, alkalis, and salts are used as pore-forming agents, and non-carbon-forming polymers are used as pore-modifying agents. This creates closed micropores and defects in the cross-linked polymerized carbon pitch, creating a structure conducive to sodium-ion storage. This approach balances high capacity and high energy density, resulting in a low-cost, simple-process, tunable disorder, high carbon yield, and suitable for large-scale production carbon material, which is then applied as an anode material in sodium-ion secondary batteries.

[0006] To address the aforementioned technical problems, this invention provides a method for preparing a sodium-ion battery anode material, comprising the following steps:

[0007] (S1) Mix asphalt-based substances evenly in the presence of sulfur-containing compounds to obtain mixed precursor I;

[0008] (S2) The mixed precursor is pressed into sheets, heat-treated in an oxidizing atmosphere, and cooled to obtain cross-linked modified asphalt. The cross-linked modified asphalt, pore-forming agent, and pore-modifying agent are mixed evenly to obtain mixed precursor II.

[0009] (S3) Mixed precursor II is calcined, cooled, ground, acid-washed, washed and dried under an inert atmosphere or a hydrocarbon atmosphere to obtain an amorphous sodium-ion battery anode material.

[0010] Further, in step (S1), the asphalt-like substance includes one or more mixtures of coal tar pitch, petroleum pitch, natural pitch and mesophase pitch; the sulfur-containing compound is selected from at least one of persulfate, thiosulfate, sulfur, and sulfide (polysulfide) salt; the mass ratio of the asphalt precursor to the sulfur-containing compound is 1:0.6-1.

[0011] Furthermore, the method for achieving uniform mixing in steps (S1) and (S2) includes, but is not limited to, ball milling, mechanical pulverization, and high-speed mixer, with ball milling being preferred. The process parameters for ball milling are well known in the art. In one specific embodiment of the present invention, the ball milling process parameters are a ball-to-material ratio of 10-20:1, a rotation speed of 500-1000 rpm, and a ball milling time of 10-15 h.

[0012] Further, in step (S2), the oxidizing atmosphere is at least one of air, oxygen, and ozone; the heat treatment involves heating to 300-600℃ at a rate of 1-3℃ / min and holding at that temperature for 2-5 hours. The slower heating rate in step (S2) is beneficial for forming a uniform cross-linked structure, facilitating the complete melting of the asphalt and its contact with the cross-linked copolymer and oxygen, thereby forming a more uniform and disordered cross-linked structure. This will help to cross-link and pyrolyze the asphalt molecules into short-range, mutually cross-linked graphite domains during subsequent calcination, and to allow them to bend and form a closed-cell structure conducive to sodium ion storage. Conversely, if the heating rate is too fast, the cross-linking copolymerization will be insufficient, causing localized areas of asphalt to directly condense into mesophase carbon microspheres with sheet-like ordered polymers. Subsequent high-temperature calcination will generate long-range ordered and tightly stacked graphene layers, which is detrimental to sodium ion storage.

[0013] Further, in step (S2), the pore-forming agent is selected from at least one of alkali metals, alkaline earth metal oxides, and hydroxides, such as at least one of magnesium oxide, sodium oxide, potassium oxide, calcium oxide, magnesium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide; the pore-modifying agent is a volatile non-carbon-forming substance, specifically selected from at least one of polyolefins and oils; the polyolefin is selected from at least one of polyethylene, polypropylene, and polystyrene; the oil is selected from at least one of glyceryl dodecyl ester, oleic acid, and glyceryl stearate.

[0014] Preferably, the pore-modifying agent is a polyolefin, and the oil is compounded in a ratio of 4-6:1-2. The inventors unexpectedly discovered that a certain ratio of polyolefin and oil as a pore-modifying agent can form a richer pore structure. First, polyolefins and oils can decompose into free radical-containing hydrocarbon compounds at high temperatures. While these compounds adhere to the surface of carbon materials for grafting and growth, they interact with defects and heteroatomic groups to passivate surface defects, reducing the defect rate on the material surface and pore surfaces. Simultaneously, the carbon layer generated in situ on the surface can transform some open pores into closed micropores, which is beneficial for the reversible adsorption and storage of sodium ions, thereby improving the electrochemical performance of the resulting negative electrode material.

[0015] Further, in step (S2), the mass ratio of crosslinked modified asphalt, pore-forming agent and pore-modifying agent is 1:0.2-0.4:0.05-0.1.

[0016] Further, in step (S3), the inert atmosphere is argon, and the hydrocarbon is at least one selected from methane, ethane, propane, butane, ethylene, acetylene, and toluene. Preferably, calcination is performed under a hydrocarbon atmosphere, which is beneficial for improving the electrochemical performance of the negative electrode material.

[0017] Further, in step (S3), the calcination is carried out by heating to 1000-1600℃ at a heating rate of 5-10℃ / min and calcining for 5-10 hours.

[0018] Further, in step (S3), the pickling involves placing the material in acid and stirring for 10-24 hours to remove excess metallic impurities; the washing is performed using water rinsing, and the drying is done in an oven or under vacuum. The acid is selected from at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

[0019] The sodium-ion battery anode material prepared by this invention has an irregular blocky morphology and structural features of curved graphite microcrystals of different sizes and closed pores. This invention uses asphalt as a precursor raw material, which is inexpensive and readily available. After dispersion and mixing with sulfur-containing compounds, it is heat-treated to make the asphalt polymer isotropically crosslinked to prevent the formation of mesophase carbon microspheres. It is further mixed with pore-forming agents and pore-modifying agents and calcined. After cooling to room temperature, it is acid-washed to remove the metal impurities, thus obtaining a hard carbon material for sodium-ion battery anodes with high and low voltage capacities.

[0020] The sodium-ion battery anode material obtained by this invention d 002 The value is between 0.36 and 0.38 nm.

[0021] Secondly, embodiments of the present invention provide a negative electrode sheet for a sodium-ion battery, comprising: a current collector, a binder coated on the current collector, and a sodium-ion battery negative electrode material prepared by the above-described preparation method.

[0022] Thirdly, the present invention provides a sodium-ion secondary battery, comprising a negative electrode sheet made of the sodium-ion battery negative electrode material obtained by the above-described preparation method.

[0023] This invention provides a sodium-ion battery anode material based on carbon materials and pitch, its preparation method, and its application. Using abundant and inexpensive pitch / coal as raw materials, and common, low-cost sulfur-containing compounds and alkali metals / alkaline earth metals as activators, it achieves both high capacity and high energy density. It proposes an amorphous carbon material that is low-cost, simple to prepare, has adjustable disorder, high carbon yield, and is suitable for large-scale production, and applies it as an anode material in sodium-ion secondary batteries. Sodium-ion secondary batteries using this invention's anode material exhibit high operating voltage and energy density, excellent rate performance, stable cycle performance, and good safety performance. They can be used not only as power sources for mobile devices and electric vehicles, but also as energy storage devices for renewable energy generation, smart grid peak shaving, distributed power stations, backup power supplies, or communication base stations. Attached Figure Description

[0024] Figure 1 The XRD patterns of the carbon materials in Example 1 and Comparative Example 1 of this invention are shown below.

[0025] Figure 2 This is a SEM image of the amorphous carbon anode material obtained in Example 1;

[0026] Figure 3 High-resolution transmission electron microscope (HRTEM) images of the hard carbon materials obtained in Comparative Example 1 and Example 1;

[0027] Figure 4 XRD pattern of the composite carbon material provided in Example 1;

[0028] Figure 5 The SAXS spectra provided in Embodiment 1 and Comparative Example 1 of the present invention;

[0029] Figure 6 This is a constant current charge-discharge curve diagram of a sodium-ion battery provided in Embodiment 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0030] The amorphous carbon anode material for a fossil mineral-based sodium-ion battery described in this invention will be further described below with reference to specific embodiments and accompanying drawings. However, it should be understood that the scope of protection of this invention is not limited to the following embodiments.

[0031] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0032] Example 1

[0033] (S1) Weigh 1 part by mass of coal tar pitch powder (sieved through 200 mesh), 1 part by mass of ammonium persulfate, and water equal to the mass of the above materials. Mix them and place them in a ball mill jar. Control the ball-to-material ratio to be 20:1. Set the ball mill speed to 500 rpm, in forward and reverse rotation mode, and ball mill for 10 hours. Place the mixture in an oven to dry and grind it into a fine powder. Vacuum dry to obtain mixed precursor I.

[0034] (S2) The mixed precursor is pressed into small discs with a diameter of 10 mm, and then placed in a tube furnace for calcination. The heating rate is 2℃ / min. After reaching 600℃, the temperature is held for 2 hours. After cooling to room temperature, the cross-linked modified asphalt is obtained by drying. Take 1 part by mass of cross-linked modified asphalt, 0.2 parts by mass of magnesium oxide, 0.1 parts by mass of sodium oxide, 0.075 parts by mass of polystyrene, 0.025 parts by mass of glycerol dodecyl ester, and water of equal mass to the above materials. Mix them and place them in a ball mill jar. Control the ball-to-material ratio to be 20:1. Set the ball mill speed to 500 rpm, forward and reverse rotation mode, and ball mill for 10 hours. Vacuum dry to obtain mixed precursor II.

[0035] Figure 1These are the infrared spectra of the crosslinked modified asphalt obtained in Example 1 and Comparative Example 1. It can be seen that the intermediate modified by crosslinking and copolymerizing with sulfur-containing compound additives differs significantly in functional groups from the intermediate of asphalt that directly self-polymerizes (Comparative Example 1) to form an ordered, layered mesophase. Numerous sulfur-containing, oxygen-containing, sulfone, and ammonium functional groups also appear in the spectra, indicating that the inorganic copolymerizing additives have copolymerized with the asphalt, altering its directional rearrangement structure.

[0036] (S3) Grind the mixed precursor II, sieve it through a 200-mesh sieve, and place it in a high-temperature tube furnace. In a mixed hydrocarbon gas atmosphere of toluene and acetylene in a volume ratio of 1:1, heat the mixture to 1500℃ at a rate of 10℃ / min, hold it at that temperature for 5 hours, cool it to room temperature, grind it, and then stir it in a hydrochloric acid solution for 24 hours. After washing with deionized water and drying, the amorphous carbon anode material is obtained.

[0037] Figure 1 The XRD patterns of the carbon materials in Example 1 and Comparative Example 1 of this invention show that the amorphous carbon anode with sodium ions activated by crosslinking has increased amorphousness compared to the carbon material obtained by direct calcination. The modified carbon material has a larger interlayer spacing and lower crystallinity, indicating that the average packing degree of graphite domains has decreased. The short-range ordered graphite domains are more conducive to forming a closed microporous structure when they crosslink with each other, thereby effectively storing sodium ion clusters in the low-pressure plateau region.

[0038] Figure 2 The image shows the SEM image of the amorphous carbon anode material obtained in Example 1. It can be seen that the carbon anode material obtained by calcination has an irregular morphology and a particle size of 1-20 micrometers.

[0039] Figure 3 High-resolution transmission electron microscopy (HRTEM) images of the hard carbon materials obtained in Comparative Example 1 and Example 1 show that the modified material possesses bent and closed local graphite domains, and simultaneously forms a large number of closed-pore structures. This is closely related to the improvement in capacity in the low-pressure plateau region. The formation of closed pores provides favorable conditions for the precipitation of sodium metal clusters inside the hard carbon, without affecting the diffusion of sodium ions in the negative electrode material. Furthermore, high-temperature calcination reduces the formation of oxygen-containing functional groups and defects on the surface by the activator, eliminating its influence on the coulombic efficiency of the material. This structure is completely different from the carbon material obtained by direct calcination of pitch.

[0040] Figure 4 The image shows the XRD pattern of the amorphous carbon anode material obtained in Example 1. It can be seen that the amorphous carbon anode material obtained through cross-linking activation exhibits increased amorphity, a larger average carbon interlayer spacing, and a wider carbon interlayer spacing distribution compared to the carbon material obtained through direct calcination. This is mainly attributed to the copolymer compound improving the rearrangement orientation during the carbonization process.

[0041] (S4) The obtained amorphous carbon negative electrode material, conductive additive SP, and binder CMC / SBR are mixed in a weight ratio of 94:2:4, dissolved in water, and stirred to obtain a uniform slurry. The slurry is then uniformly coated on carbon-coated aluminum foil using a 50μm scraper, dried, and sliced ​​to obtain the negative electrode sheet.

[0042] Example 2

[0043] The other operating steps are the same as in Example 1, except that in step (S1), coal tar pitch powder is replaced with petroleum pitch.

[0044] Example 3

[0045] The other operating steps are the same as in Example 1, except that in step (S1), ammonium persulfate is replaced with sodium persulfate.

[0046] Example 4

[0047] The other operating steps are the same as in Example 1, except that in step (S1), ammonium persulfate is replaced with sodium thiosulfate.

[0048] Example 5

[0049] The other operating steps are the same as in Example 1, except that in step (S1), ammonium persulfate is replaced with sulfur.

[0050] Example 6

[0051] The other operating steps are the same as in Example 1, except that in step (S2), magnesium oxide is replaced with sodium oxide.

[0052] Example 7

[0053] The other operating steps are the same as in Example 1, except that in step (S2), magnesium oxide is replaced with magnesium hydroxide.

[0054] Example 8

[0055] The other operating steps are the same as in Example 1, except that in step (S2), 0.075 parts by mass of polystyrene and 0.025 parts by mass of glyceryl dodecanoate are replaced with 0.06 parts by mass of polystyrene and 0.01 parts by mass of oleic acid.

[0056] Example 9

[0057] The other operating steps are the same as in Example 1, except that in step (S2), 0.075 parts by mass of polystyrene and 0.025 parts by mass of glyceryl dodecanoate are replaced with 0.04 parts by mass of polyethylene and 0.01 parts by mass of glyceryl stearate.

[0058] Example 10

[0059] The other operating steps are the same as in Example 1, except that in step (S2), 0.075 parts by weight of polystyrene and 0.025 parts by weight of glyceryl dodecanoate are replaced with 0.05 parts by weight of polystyrene and 0.05 parts by weight of glyceryl stearate.

[0060] Example 11

[0061] The other operating steps are the same as in Example 1, except that in step (S2), 0.075 parts by mass of polystyrene and 0.025 parts by mass of dodecyl glycerol are replaced with 0.1 parts by mass of polystyrene.

[0062] Example 12

[0063] The other operating steps are the same as in Example 1, except that in step (S2), 0.075 parts by mass of polystyrene and 0.025 parts by mass of dodecyl glycerol are replaced with 0.1 parts by mass of dodecyl glycerol.

[0064] Example 13

[0065] The other operating steps are the same as in Example 1, except that in step (S2), the heating rate is changed from 2℃ / min to 10℃ / min.

[0066] Comparative Example 1

[0067] All cross-linking activation steps were eliminated, and the coal tar pitch was directly calcined at 1300℃.

[0068] Figure 5 The SAXS spectra provided in Embodiment 1 and Comparative Example 1 of the present invention; from Figure 5 The SAXS spectra of the carbon materials before and after modification were analyzed and fitted using the following model:

[0069]

[0070] Where q is the scattering vector, A and B are proportional to the total volume of the large and small pores, and D is the constant background scattering.

[0071] Since parameter B is proportional to the total micropore volume in the carbon material, a quantitative comparison of the porosity can be obtained by comparing the B values ​​of Example 1 and Comparative Example 1. Furthermore, the Guinier plateau near q = 0.1 indicates that the carbon material obtained in Example 1 possesses a large number of micropores, while Comparative Example 1 does not exhibit a Guinier plateau in the range of q = 0.01-1, meaning it lacks micropores of 1-10 nm. It can be seen that, compared to directly calcined pitch materials, pitch-based hard carbon materials copolymerized with inorganic materials and with adjusted pore structure exhibit higher porosity and internal surface area. The newly formed pores facilitate the adsorption and deposition of sodium ions and sodium clusters on their inner surface.

[0072] Application examples Electrochemical performance testing

[0073] The dried negative electrode sheet was assembled into a coin cell with a sodium metal negative electrode, a carboxylic acid cellulose membrane, and EC / DEC / 1M NaPF6 electrolyte. The cell was then placed on a LAND test platform for testing, yielding the first cycle curve shown in Table 1. Within the voltage range of 0.001–2V, the cell was first activated for 5 cycles at a current density of 20 mA / g, followed by charge-discharge cycling.

[0074] Figure 6 The first-cycle charge-discharge curves of Example 1 are presented. Compared with the direct calcination of Comparative Example 1, the modified carbon material exhibits a significantly improved capacity and a distinct plateau-slope composite curve, indicating a change in the main sodium storage mechanism.

[0075] The electrochemical performance of the negative electrode materials obtained in the above embodiments and comparative examples is listed in Table 1 below:

[0076] Table 1 Electrochemical performance data

[0077]

[0078]

[0079] The test results of the half-cells in Table 1 for each embodiment show that the low-voltage plateau capacity of the amorphous carbon anode in sodium-ion batteries is significantly improved after cross-linking and activation of fossil mineral precursors such as pitch, and the specific capacity is also further improved. For example, in Example 1, the carbon anode material modified with ammonium sulfate has a capacity of 327 mAh g⁻¹. -1 Total capacity up to 200mAh g -1 The modified example exhibits a low-pressure plateau capacity, while the unmodified comparative example 1 has a specific capacity of only 65 mAh / g, with almost no low-pressure plateau. It is worth noting that the crosslinking activation conditions need to be properly controlled; by controlling the activation conditions, the optimal carbon layer structure and the maximum specific capacity can be obtained.

[0080] This invention provides an application of fossil mineral-based pyrolytic amorphous carbon material in sodium-ion batteries. Its contribution to the prior art lies in the cross-linking and pore-forming effect of an activator during the pyrolysis of fossil minerals, which inhibits the long-range ordered rearrangement of the carbon layer, leading to the local cross-linking and closure of graphite domains to form closed pores. This enhances sodium-ion storage in the low-pressure region and significantly improves the electrochemical performance of the sodium-ion battery. It is understood that while the various embodiments of this invention have described the invention in detail with specific electrolytes, separators, current collectors, active materials, binders, conductive additives, etc., these descriptions are merely for fulfilling legal requirements and illustrating the composition of sodium-ion batteries. This invention is not limited to the given embodiments. Any modifications, equivalent substitutions, and improvements made using this specification within the spirit and principles of this invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this invention.

Claims

1. A method for preparing a sodium-ion battery anode material, characterized in that, Includes the following steps: (S1) Mix asphalt-based substances evenly in the presence of sulfur-containing compounds to obtain mixed precursor I; (S2) The mixed precursor is pressed into sheets, heat-treated in an oxidizing atmosphere, and cooled to obtain crosslinked modified asphalt. The crosslinked modified asphalt, pore-forming agent, and pore-modifying agent are mixed evenly to obtain mixed precursor II. The pore-modifying agent is a polyolefin, and the oil is compounded in a ratio of 4-6:1-2. The polyolefin is selected from at least one of polyethylene, polypropylene, and polystyrene. The oil is selected from at least one of glyceryl dodecyl ester, oleic acid, and glyceryl stearate. The mass ratio of crosslinked modified asphalt, pore-forming agent, and pore-modifying agent is 1:0.2-0.4:0.05-0.

1. (S3) Mixed precursor II is calcined, cooled, ground, acid-washed, washed and dried under an inert atmosphere or a hydrocarbon atmosphere to obtain an amorphous sodium-ion battery anode material.

2. The preparation method according to claim 1, characterized in that, In step (S1), the asphalt-like substance includes one or more mixtures of coal tar pitch, petroleum pitch, natural pitch and mesophase pitch; the sulfur-containing compound is selected from at least one of persulfate, thiosulfate, sulfur and sulfide; the mass ratio of the asphalt-like substance to the sulfur-containing compound is 1:0.6-1.

3. The preparation method according to claim 1, characterized in that, In step (S2), the oxidizing atmosphere is at least one of air, oxygen, and ozone; the heat treatment involves heating to 300-600℃ at a heating rate of 1-3℃ / min and holding at that temperature for 2-5 hours.

4. The preparation method according to claim 1, characterized in that, In step (S2), the pore-forming agent is selected from at least one of alkali metals, oxides of alkaline earth metals, and hydroxides.

5. The preparation method according to claim 4, characterized in that, The pore-forming agent is selected from at least one of magnesium oxide, sodium oxide, potassium oxide, calcium oxide, magnesium hydroxide, sodium hydroxide, potassium hydroxide, and calcium hydroxide.

6. The preparation method according to claim 1, characterized in that, In step (S3), the inert atmosphere is argon, and the hydrocarbon is at least one of methane, ethane, propane, butane, ethylene, acetylene, and toluene.

7. The preparation method according to claim 1, characterized in that, In step (S3), the calcination is carried out by heating the temperature to 1000-1600℃ at a heating rate of 5-10℃ / min and calcining for 5-10 hours.

8. The preparation method according to claim 1, characterized in that, In step (S3), the pickling involves placing the material in acid and stirring for 10-24 hours; the washing involves rinsing with water; and the drying involves drying in an oven or under vacuum. The acid is selected from at least one of hydrochloric acid, sulfuric acid, phosphoric acid, and nitric acid.

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