Method for accelerating growth speed of aluminum-doped cobaltosic oxide crystal nucleus through auxiliary oxidation

Abstract

The invention discloses a method for accelerating the growth speed of an aluminum-doped cobaltosic oxide crystal nucleus through auxiliary oxidation, and belongs to the technical field of cobalt compounds. The method has the advantages of simple operation and low cost; by using the oxidizing substance, the growth environment of the crystal nucleus can be improved, the quality and the stability of the crystal nucleus can be improved, and the growth speed of the hydroxyl system aluminum-doped cobaltosic oxide crystal nucleus can be obviously accelerated, so that the production efficiency is improved, and industrial production is easy to realize.

Description

Technical Field

[0001] The invention relates to the technical field of cobalt compounds, in particular to a method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei through auxiliary oxidation. Background Art

[0002] Lithium cobalt oxide is an inorganic compound and a layered oxide material, which is widely used as the positive electrode material of lithium-ion batteries. It has a high specific capacity, good cycle performance and high operating voltage. It is one of the most widely used positive electrode materials in commercial lithium-ion batteries and is widely used in the 3C digital field, including digital cameras, mobile phones, drones, wireless headphones and other products. Lithium cobalt oxide is calcined at a certain temperature by cobalt oxide and lithium carbonate. Therefore, the quality of cobalt oxide will affect the quality of the finished product of lithium cobalt oxide. When using aluminum-doped cobalt oxide for preparation, the stability of aluminum element during the charging and discharging process can be used to stabilize the structure of lithium cobalt oxide and further optimize the quality of the finished product.

[0003] At present, the method of preparing cobalt tetroxide by precipitation reaction and calcination of sodium hydroxide and soluble cobalt salt is generally used in this field. This process has the advantages of simple preparation, strong designability and cost-effectiveness. Similarly, aluminum-doped cobalt tetroxide can be prepared by wet aluminum-doped cobalt tetroxide synthesis process. For example, the applicant's research and development team provides a method for preparing aluminum-doped cobalt tetroxide in the Chinese invention patent with publication number CN112390297A, which includes the following steps: ① Prepare a certain concentration of aluminum-cobalt mixed solution, precipitant solution, and complexing agent solution; ② Add the aluminum-cobalt mixed solution, precipitant solution, and complexing agent solution to the reactor in a parallel flow manner to control the pH value and reaction temperature of the reaction system; ③ After the overflow begins, measure the specific gravity of the mother liquor every 1-2 hours, and control the specific gravity of the mother liquor between 1-1.1 by adding pure water; ④ When the particle size D50 of aluminum-doped cobalt tetroxide reaches 3-5 μm, stop the reaction, centrifuge washing, drying, and calcination. The invention controls the specific gravity of the mother liquor in the reaction system within a certain reasonable range, thus avoiding the situation where the particle dispersion and growth are affected by the excessive specific gravity of the mother liquor. However, in the further actual production process, the R&D team noticed that in this type of sodium hydroxide synthesis system, there is still a technical problem that the crystal nucleus growth rate is slow and it is difficult to meet the needs of enterprises for efficient production, which restricts its industrial production application.

[0004] During the synthesis of aluminum-doped cobalt oxide, the growth rate of the crystal nucleus has an important influence on the performance and quality of the product. Therefore, providing a new method to accelerate the growth rate of the crystal nucleus is not only conducive to improving production efficiency, but also helps to promote the optimization of the quality of aluminum-doped cobalt oxide finished products, which has positive significance for expanding its application in the fields of positive electrode materials. Summary of the invention

[0005] In view of the above-mentioned defects of the prior art, in a first aspect of the present invention, a method for accelerating the growth rate of aluminum-doped cobalt oxide crystal nuclei by auxiliary oxidation with fast crystal nuclei growth rate and high finished product quality is provided, comprising the following steps: (1) preparing an aluminum-cobalt mixed solution, a precipitant solution, and a complexing agent solution; using air as an oxidant and hydrogen peroxide or sodium hypochlorite as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution to obtain an aluminum-cobalt reaction solution; (2) adding the aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution to the reaction device in parallel; wherein air and the cobalt-aluminum mixed solution are injected into the reaction device through a spray device; and controlling the pH value and temperature of the reaction system; (3) Starting from the overflow, the specific gravity of the mother liquor in the reaction system is measured at each cycle, and the specific gravity of the mother liquor is controlled at 0.8-1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, stop the reaction and perform filter pressing, washing, drying and calcination.

[0006] In the actual production of the present invention, the cost of air can be ignored, but oxygen is used as a gaseous oxidant. When oxidized by air alone without an auxiliary oxidant, the reaction involves the gas-liquid-solid three-phase interface, which makes diffusion difficult. In addition, the solubility of oxygen in water is limited, and the reaction speed is slow. However, using hydrogen peroxide or sodium hypochlorite as an auxiliary oxidant can effectively diffuse, so that the reactants are more fully contacted, the reaction speed can be increased, and the cost can be well controlled.

[0007] During the precipitation reaction, the cobalt ions and their doped aluminum ions are appropriately controlled within a suitable range. Too high or too low a cobalt ion concentration is not conducive to the uniform growth and crystallization of the particles, and affects the particle size and morphology of the final product. An appropriate cobalt ion concentration can accelerate the reaction process, shorten the reaction time, and improve production efficiency. By adjusting the cobalt concentration, the particle size and morphology of the final product can be adjusted to a certain extent, thereby improving the diversity and applicability of the product. In addition, an appropriate aluminum ion concentration can control the doped aluminum within a suitable range and stabilize the structure of the downstream product lithium cobalt oxide.

[0008] Preferably, in step (1), the aluminum-cobalt mixed solution is prepared by dissolving soluble cobalt salt and aluminum salt in water; in the aluminum-cobalt mixed solution, the cobalt concentration is 90-160 g / L, and the aluminum concentration is 1.0-1.5 g / L.

[0009] Cobalt salts and aluminum salts can be selected from salts with good solubility in water so that they can maintain a high ion concentration in the solution, which is conducive to efficient precipitation reactions. Cobalt sulfate, cobalt chloride, cobalt nitrate, etc., aluminum chloride, aluminum sulfate, aluminum acetate, etc. are common chemicals with low prices and wide sources, and are particularly suitable for large-scale industrial production.

[0010] Further preferably, the cobalt salt includes at least one of cobalt sulfate, cobalt chloride and cobalt nitrate; and the aluminum salt includes at least one of aluminum chloride, aluminum sulfate and aluminum acetate.

[0011] The concentration of the precipitant affects the efficiency of the reaction and the recovery rate of cobalt, so it needs to be controlled within an appropriate range to reduce unnecessary waste. Sodium hydroxide and potassium hydroxide are inexpensive and widely available, making them particularly suitable precipitants.

[0012] Preferably, in step (1), the precipitant solution is prepared by dissolving a precipitant in water; the precipitant comprises at least one of sodium hydroxide and potassium hydroxide; and the concentration of the precipitant is 180-260 g / L.

[0013] The concentration of the complexing agent affects the complexing state of the cobalt ions. By controlling the concentration, the cobalt ions can be uniformly precipitated to form regular particles, so as to better control the precipitation morphology and make it present an ideal form. In the present invention, the complexing agent is preferably sodium citrate, ethylenediaminetetraacetic acid, sodium pyrophosphate, etc.

[0014] Preferably, in step (1), the complexing agent solution is prepared by dissolving a complexing agent in water; the complexing agent includes at least one of sodium citrate, ethylenediaminetetraacetic acid, and sodium pyrophosphate; and the concentration of the complexing agent is 0.1-0.5 g / L.

[0015] Preferably, in step (1), the concentration of the auxiliary oxidant in the aluminum-cobalt reaction solution is 0.01-0.25 g / L.

[0016] Preferably, in step (2), the volume ratio of air to the cobalt-aluminum mixed liquid is 10:1.

[0017] During the liquid mixing process, the appropriate flow rate can ensure that the reaction solution is fully mixed in the reactor, avoiding local concentrations that are too high or too low, thereby ensuring the uniformity of the reaction. The control of the flow rate will also affect the formation and growth of the precipitate. If the flow rate is too fast, the precipitate particles may be too small or uneven, affecting the quality of the product. In addition, the appropriate flow rate can also improve the reaction efficiency, reduce the reaction time, and thus improve production efficiency.

[0018] Preferably, in step (2), the flow rate of the aluminum-cobalt reaction solution is 140-180 L / h; and the flow rate of the precipitant solution is 110-260 L / h.

[0019] In a reaction environment with a pH value of 9.1-10.9 and a temperature of 45-78°C, the precipitation reaction can be carried out effectively, the precipitation efficiency of cobalt is high, the size and distribution of cobalt particles are more uniform, and the stability is good.

[0020] Preferably, in step (2), the pH value of the reaction system is 9.1-10.9, and the temperature is 45-78°C.

[0021] Preferably, in step (3), each cycle lasts for 2-4 hours.

[0022] In actual operation, after the precipitation reaction in the reactor is completed, the reactor can be divided for subsequent filter pressing, washing, calcination and other operations. This can improve the treatment effect and production efficiency and optimize the quality of the finished product. The conductivity can be used as an indicator to reflect the residual ions in the washing liquid. When its conductivity is low, it can be regarded as that the impurity ions have been eluted from the precipitation, which helps to improve the purity of the finished product. In general, the precipitation needs to be washed several times to achieve the expected effect. After one round of operation, it can be reset in the reactor for the next round of filter pressing and washing until the conductivity of the washing liquid is lower than the preset value.

[0023] Preferably, in step (4), washing is performed until the conductivity of the washing liquid is lower than 20 S / m.

[0024] Staged calcination helps reduce particle cracking and makes the structure and properties of the finished product more stable.

[0025] Preferably, in step (4), the calcination procedure is as follows: first calcining at 150-260°C for 2-6 h, then calcining at 350-480°C for 2-6 h, and finally calcining at 650-780°C for 2-6 h.

[0026] Compared with the prior art, the present invention has the following advantages and beneficial effects: The invention provides a method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation. The method has the advantages of simple operation and low cost. The use of the oxidizing substance can improve the growth environment of the crystal nuclei, improve the quality and stability of the crystal nuclei, significantly accelerate the growth rate of the aluminum-doped cobalt tetroxide crystal nuclei of the hydroxyl system, improve the production efficiency, and facilitate industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a process flow chart of an embodiment. DETAILED DESCRIPTION

[0028] The present invention is further described below by way of examples, but the present invention is not limited to the scope of the examples. The experimental methods in the following examples without specifying specific conditions are carried out according to conventional methods and conditions, or selected according to the product specifications.

[0029] Example 1 A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, such as Figure 1 As shown, the steps are as follows: (1) preparing an aluminum-cobalt mixed solution (wherein the cobalt solution concentration is 140 g / L, using cobalt chloride; the aluminum concentration is 1.1 g / L, using aluminum chloride), a precipitant solution (32 wt.% sodium hydroxide aqueous solution), and a complexing agent solution (with a concentration of 0.12 g / L, using EDTA); using air as an oxidant and hydrogen peroxide as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution (with a concentration of 0.025 g / L) to obtain an aluminum-cobalt reaction solution; (2) The aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution were continuously added to the reactor in parallel, with the flow rate of the cobalt-aluminum mixed solution being 180 kg / h and the flow rate of the precipitant being 110 L / h. Air and the cobalt-aluminum mixed solution (10:1, v / v) were injected into the reactor through an ejector. The pH value of the reaction system was controlled to be 9.8 and the reaction temperature to be 68 °C. (3) Starting from the overflow, measure the specific gravity of the mother liquor in the reaction system every 2 hours, and control the specific gravity of the mother liquor to be between 0.8 and 1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, the reaction is stopped, and the mixture is separated into separate kettles for filter pressing, washing (3 times or more, and the next operation can be reset in the reactor after one round of operation until the conductivity of the washing liquid is lower than 20 S / m), drying, and calcination in a roller kiln. The calcination procedure is: first calcination at 150 °C for 3 h, then calcination at 350 °C for 5 h, and finally calcination at 680 °C for 3 h.

[0030] Example 2 A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, comprising the following steps: (1) preparing an aluminum-cobalt mixed solution (wherein the cobalt solution concentration is 140 g / L, using cobalt chloride; the aluminum concentration is 1.1 g / L, using aluminum chloride), a precipitant solution (a 32 wt.% sodium hydroxide aqueous solution), and a complexing agent solution (with a concentration of 0.12 g / L, using EDTA); using air as an oxidant and sodium hypochlorite as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution (with a concentration of 0.025 g / L) to obtain an aluminum-cobalt reaction solution; (2) The aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution were continuously added to the reactor in parallel, with the flow rate of the cobalt-aluminum mixed solution being 180 kg / h and the flow rate of the precipitant being 110 L / h. Air and the cobalt-aluminum mixed solution (10:1, v / v) were injected into the reactor through an ejector. The pH value of the reaction system was controlled to be 9.8 and the reaction temperature to be 68 °C. (3) Starting from the overflow, measure the specific gravity of the mother liquor in the reaction system every 2 hours, and control the specific gravity of the mother liquor to be between 0.8 and 1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, the reaction is stopped, and the mixture is separated into separate kettles for filter pressing, washing (3 times or more, and the next operation can be reset in the reactor after one round of operation until the conductivity of the washing liquid is lower than 20 S / m), drying, and calcination in a roller kiln. The calcination procedure is: first calcination at 150 °C for 3 h, then calcination at 350 °C for 5 h, and finally calcination at 680 °C for 3 h.

[0031] Example 3 A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, comprising the following steps: (1) preparing an aluminum-cobalt mixed solution (wherein the cobalt solution concentration is 90 g / L, using cobalt sulfate; the aluminum concentration is 1.0 g / L, using aluminum sulfate), a precipitant solution (a 180 g / L potassium hydroxide aqueous solution), and a complexing agent solution (a concentration of 0.10 g / L, using sodium citrate); using air as an oxidant and sodium hypochlorite as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution (concentration of 0.01 g / L) to obtain an aluminum-cobalt reaction solution; (2) The aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution were continuously added to the reactor in parallel, with the flow rate of the cobalt-aluminum mixed solution being 140 kg / h and the flow rate of the precipitant being 110 L / h. Air and the cobalt-aluminum mixed solution (10:1, v / v) were injected into the reactor through an ejector. The pH value of the reaction system was controlled to be 9.1 and the reaction temperature to be 78 °C. (3) Starting from the overflow, measure the specific gravity of the mother liquor in the reaction system every 2 hours, and control the specific gravity of the mother liquor to be between 0.8 and 1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, stop the reaction, separate the kettle, filter press, wash (3 times or more, after one round of operation, the next round of operation can be reset in the reactor until the conductivity of the washing liquid is lower than 20 S / m), dry, and calcine in a roller kiln. The calcination procedure is: first calcine at 260 °C for 2 h, then calcine at 480 °C for 2 h, and finally calcine at 780 °C for 2 h.

[0032] Example 4 A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, comprising the following steps: (1) preparing an aluminum-cobalt mixed solution (wherein the cobalt solution concentration is 160 g / L, using cobalt nitrate; the aluminum concentration is 1.5 g / L, using aluminum acetate), a precipitant solution (260 g / L sodium hydroxide aqueous solution), and a complexing agent solution (with a concentration of 0.5 g / L, using sodium pyrophosphate); using air as an oxidant and sodium hypochlorite as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution (with a concentration of 0.025 g / L) to obtain an aluminum-cobalt reaction solution; (2) The aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution were continuously added to the reactor in parallel, with the flow rate of the cobalt-aluminum mixed solution being 180 kg / h and the flow rate of the precipitant being 260 L / h. Air and the cobalt-aluminum mixed solution (10:1, v / v) were injected into the reactor through an ejector. The pH value of the reaction system was controlled to be 10.9 and the reaction temperature to be 45 °C. (3) Starting from the overflow, measure the specific gravity of the mother liquor in the reaction system every 2 hours, and control the specific gravity of the mother liquor to be between 0.8 and 1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, stop the reaction, separate the kettle, filter press, wash (3 times or more, after one round of operation, the next round of operation can be reset in the reactor until the conductivity of the washing liquid is lower than 20 S / m), dry, and put into a roller kiln for calcination. The calcination procedure is: first calcination at 150 °C for 6 h, then calcination at 350 °C for 6 h, and finally calcination at 650 °C for 6 h.

[0033] Comparative Example 1 A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, comprising the following steps: (1) Prepare an aluminum-cobalt mixed solution (wherein the cobalt solution concentration is 140 g / L, using cobalt chloride; the aluminum concentration is 1.1 g / L, using aluminum chloride), a precipitant solution (32 wt.% sodium hydroxide aqueous solution), and a complexing agent solution (with a concentration of 0.12 g / L, using EDTA); use air as the oxidant, and do not add an auxiliary oxidant; (2) The aluminum-cobalt mixed solution, the precipitant solution, and the complexing agent solution were continuously added to the reactor in parallel, with the flow rate of the cobalt-aluminum mixed solution being 180 kg / h and the flow rate of the precipitant being 110 L / h. Air and the cobalt-aluminum mixed solution (10:1, v / v) were injected into the reactor through an ejector. The pH value of the reaction system was controlled to be 9.8 and the reaction temperature to be 68 °C. (3) Starting from the overflow, measure the specific gravity of the mother liquor in the reaction system every 2 hours, and control the specific gravity of the mother liquor to be between 0.8 and 1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, the reaction is stopped, and the mixture is separated into separate kettles for filter pressing, washing (3 times or more, and the next operation can be reset in the reactor after one round of operation until the conductivity of the washing liquid is lower than 20 S / m), drying, and calcination in a roller kiln. The calcination procedure is: first calcination at 150 °C for 3 h, then calcination at 350 °C for 5 h, and finally calcination at 680 °C for 3 h.

[0034] During the preparation of Examples 1 and 2 and Comparative Example 1, samples were taken every 2 hours and the sample size was tested by a Malvern 3000 laser particle size analyzer. The crystal growth rate was calculated based on the D50 difference. The test results of the crystal nucleus growth rate are shown in Table 1.

[0035] Table 1: Crystal nucleus growth rate test results

[0036] It can be seen from the above test results that the use of oxidizing substances can improve the growth environment of the crystal nucleus, improve the quality and stability of the crystal nucleus, significantly accelerate the growth rate of the hydroxyl system aluminum-doped cobalt tetroxide crystal nucleus, and improve production efficiency. This method has the advantages of simple operation and low cost, and is easy to realize industrial production.

[0037] The preferred specific embodiments of the present invention are described in detail above. It should be understood that a person skilled in the art can make many modifications and changes based on the concept of the present invention without creative work. Therefore, any technical solution that can be obtained by a person skilled in the art through logical analysis, reasoning or limited experiments based on the concept of the present invention on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. A method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation, characterized in that: The steps include: (1) preparing an aluminum-cobalt mixed solution, a precipitant solution, and a complexing agent solution; using air as an oxidant and hydrogen peroxide or sodium hypochlorite as an auxiliary oxidant; adding the auxiliary oxidant to the aluminum-cobalt mixed solution to obtain an aluminum-cobalt reaction solution; (2) adding the aluminum-cobalt reaction solution, the precipitant solution, and the complexing agent solution to the reaction device in parallel; wherein air and the cobalt-aluminum mixed solution are injected into the reaction device through a spray device; adding an auxiliary oxidant to control the pH value and temperature of the reaction system; (3) Starting from the overflow, the specific gravity of the mother liquor in the reaction system is measured at each cycle, and the specific gravity of the mother liquor is controlled at 0.8-1.2 by adding pure water; (4) When the particle size D50 of aluminum-doped cobalt oxide reaches 3.3-5.5 μm, stop the reaction and perform filter pressing, washing, drying and calcination.

2. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (1), the aluminum-cobalt mixed solution is prepared by dissolving soluble cobalt salt and aluminum salt in water; in the aluminum-cobalt mixed solution, the cobalt concentration is 90-160 g / L, and the aluminum concentration is 1.0-1.5 g / L; the cobalt salt includes at least one of cobalt sulfate, cobalt chloride, and cobalt nitrate; and the aluminum salt includes at least one of aluminum chloride, aluminum sulfate, and aluminum acetate.

3. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (1), the precipitant solution is prepared by dissolving a precipitant in water; the precipitant includes at least one of sodium hydroxide and potassium hydroxide; and the concentration of the precipitant is 180-260 g / L.

4. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (1), the complexing agent solution is prepared by dissolving a complexing agent in water; the complexing agent includes at least one of sodium citrate, ethylenediaminetetraacetic acid, and sodium pyrophosphate; and the concentration of the complexing agent is 0.1-0.5 g / L.

5. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (1), the concentration of the auxiliary oxidant in the aluminum-cobalt reaction solution is 0.01-0.25 g / L.

6. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (2), the volume ratio of air to the cobalt-aluminum mixed liquid is 10:

1.

7. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (2), the flow rate of the aluminum-cobalt reaction solution is 140-180 L / h; the flow rate of the precipitant solution is 110-260 L / h.

8. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (2), the pH value of the reaction system is 9.1-10.9, and the temperature is 45-78°C.

9. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (4), washing is performed until the conductivity of the washing liquid is lower than 20 S / m.

10. The method for accelerating the growth rate of aluminum-doped cobalt tetroxide crystal nuclei by auxiliary oxidation according to claim 1, characterized in that: In the step (4), the calcination procedure is as follows: first calcining at 150-260°C for 2-6 h, then calcining at 350-480°C for 2-6 h, and finally calcining at 650-780°C for 2-6 h.

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