CN1544340A - Preparation method of tricobalt tetroxide for lithium ion battery - Google Patents

Abstract

The invention discloses a process for preparing cobalto-cobaltic oxide for used in lithium ion battery, wherein cobalt oxalate or cobalt hydroxide or cobaltous carbonate is used as raw material for three segment calcinations, during which the thermal cracking and oxidization of cobalt salt are divided into two procedures, no oxidation agent is provided during the thermal cracking of the cobalt salt, thus converting all of them into cobaltous oxide, then temperature is elevated to oxidization temperature and oxygen of air atmosphere is provided, so as to converting all cobaltous oxide into cobaltic-cobaltous oxide. The product made thereby has high conversion rate of cobaltic-cobaltous oxide, less cobalt oxidates of other forms, epigranularity and apparent density.

Description

Preparation method of tricobalt tetroxide for lithium ion battery

technical field

The invention relates to the field of preparation of metal oxides, and provides a preparation method of tricobalt tetroxide which can be used as a raw material of lithium cobaltate, a positive electrode material of a lithium ion battery.

Background technique

The positive electrode material in lithium-ion batteries is mainly lithium cobalt oxide, and the key material for preparing lithium cobalt oxide is tricobalt tetroxide. and lifespan, etc. have a significant impact. There are strict requirements on the chemical composition of cobalt tetroxide used in batteries. The more economical and practical method for preparing cobalt tetroxide in the prior art is the calcining thermal decomposition method, that is: cobalt salts such as cobalt carbonate, cobalt hydroxide or cobalt oxalate at high temperature Calcined to obtain tricobalt tetroxide.

Cobalt is a variable-valence element (2-valence, 3-valence), and its oxides include cobaltous oxide (CoO), dicobaltous oxide (Co ₂ O ₃ ) and tricobaltous oxide (Co ₃ O ₄ ), among which tricobaltous oxide is used as a battery raw material. most. Experiments show that if the heating temperature, heating time and gas atmosphere in the heating space are not properly controlled during the calcination thermal decomposition process, more CoO or Co ₂ O ₃ will appear, which will reduce the production rate of Co ₃ O ₄ in the product , thus affecting the quality of lithium cobalt oxide. In addition, Co ₃ O ₄ used as a battery raw material also has special requirements for its physical indicators, especially particle size composition, distribution and bulk density. Generally, it is required that the particle size is relatively uniform and the bulk density is relatively large. For high-power batteries used in power sources, the requirements for particle size distribution and bulk density are more stringent. The control of various operating conditions in the calcination process also affects the particle size and bulk density of the product. All of the above contents have not been paid enough attention in the prior art. The calcination of cobalt salt in the prior art is usually placed in a calcination furnace, and air or oxygen is introduced to carry out a period of calcination, such as the "manufacturing method of tricobalt tetroxide" disclosed in the publication specification of the invention patent application with the publication number CN1376638A. In addition, the particle size and bulk density of Co ₃ O ₄ products also have a great influence on the particle size and particle morphology of its precursor cobalt salt, and the control of various operating conditions in the preparation of cobalt salt is also very important, but in the present There are technologies that are not covered.

Contents of the invention

The object of the present invention is to provide a kind of preparation method of tricobalt tetroxide used as the high-power battery raw material of lithium ion battery and power source, the transformation rate of tricobalt tetroxide in the product made by this method is high, and other oxides of cobalt are few, and The particle size is uniform and the bulk density is large, which is beneficial to improve the electrical performance and service life of the battery.

The purpose of the present invention is achieved like this:

Using cobalt oxalate or cobalt hydroxide or cobalt carbonate as raw material, the particle size of the cobalt salt is D ₅₀ =2-8 μm;

The method for preparing tricobalt tetroxide, the steps are: the above-mentioned raw materials are subjected to three-stage calcination:

A. One stage calcination:

The cobalt salt powder is placed in a calcining equipment and heated at a heating temperature of 200-450°C, preferably at a heating temperature of 250-350°C, for a heating time of 2-5 hours, and the calcining equipment is a nitrogen atmosphere; the process is to use Removal of residual water and/or water of crystallization in cobalt salt powder;

B. Two-stage calcination:

Heat the material treated in the previous step at a temperature of 500-800°C, preferably at a temperature of 550-700°C, and for a heating time of 1-5 hours, and the calcination equipment is still in a nitrogen atmosphere; during this process, the cobalt salt is heated Cracked into cobaltous oxide;

C. Three-stage calcination:

Heat the material treated in the previous step at a temperature of 700-1000°C, preferably at a temperature of 750-850°C, and for a heating time of 2-8 hours, in an air or oxygen atmosphere in the calcining equipment; Cobalt is oxidized to tricobalt tetroxide;

Then, place the above-mentioned tricobalt tetroxide powder at room temperature to cool, and finally pack into finished products.

In the above method, the materials are calcined at three temperatures respectively, and the atmospheres in the calcining equipment are different. First, there is a pretreatment stage, where the cobalt salt is dehydrated at a lower temperature. This step has a greater impact on the subsequent decomposition and oxidation processes. If the cobalt salt contains a certain amount of water, the thermal decomposition and oxidation It will be precipitated, which will cause the powder particles to bond, thereby affecting the particle size and crystal form of the finished product, and also affecting the oxidation process, resulting in insufficient oxidation and a decrease in the conversion rate of cobalt tetroxide. A calcination stage is set, and the heating temperature of this section is relatively low. , and a nitrogen atmosphere is formed in this process, and another function is to avoid grain growth, ensure that the spherical grain shape of the cobalt salt is maintained, and increase the bulk density of the final product to achieve the production of cobalt acid in lithium-ion battery materials. Lithium raw material requirements. In this one-stage and two-stage calcination process, the flow rate of nitrogen also affects the control of particle size. If the nitrogen flow rate is large, the grains will not grow up, but if the nitrogen flow rate is small, the grains will grow. Generally, the nitrogen flow rate is controlled. The flow rate is 3-5M ³ /min. The prominent feature of this method is to separate the thermal cracking and oxidation process of cobalt salts during the calcination process, provide a nitrogen atmosphere during thermal cracking, and the temperature is higher than the first-stage calcination, but lower than the third-stage calcination, so that all the cobalt salts are converted first Become cobaltous oxide, then, raise temperature again and provide air or oxygen atmosphere to make cobaltous oxide change into tricobalt tetroxide, like this, can guarantee the conversion rate of very high cobaltous oxide and make the amount of cobaltous oxide and dicobaltous oxide in the final product It is reduced to less than 1% so that cobaltous oxide and dicobaltous oxide are substantially not contained. However, in many similar technologies disclosed in the prior art, the cobalt salt is directly placed at the temperature of thermal cracking and air or oxygen is introduced during the calcination process. The product processed in this way may contain about 73% cobalt element, but in fact it contains a lot of cobaltous oxide and cobalt trioxide, which can be seen from the X-ray diffraction diagram, and can even be It can be seen from the appearance color of the product.

It can be seen from the above that in the aforementioned method, the crystal grain shape of the cobalt salt powder is preferably spherical. The cobalt salt of this quasi-spherical grain can be made with following chemical precipitation method, and its steps are:

(1) the step of preparing cobalt oxalate:

a, preparation of cobalt salt aqueous solution, cobalt salt can be cobalt chloride or cobalt sulfate, its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4 -1.2;

b, configure ammonium oxalate precipitant solution, its concentration is 60-120 g/liter, and pass into ammonia to make the pH of described precipitant aqueous solution be 3-5; Can also add dispersant in this solution, it can be poly Hexylene glycol (molecular weight is 4000), or butadiene, or acrylic acid, or a mixture of butadiene and acrylic acid, the amount of the dispersant added is 2-8 grams per 10 liters of ammonium oxalate aqueous solution That's it.

c. Spray the ammonium oxalate precipitant aqueous solution into the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution into the ammonium oxalate precipitant aqueous solution, and the ratio of the cobalt salt and the ammonium oxalate precipitant solution meets the requirements of the reaction of the two substances The amount specified in the equation, until the pH of the mixed solution reaches 1-1.5, the reaction temperature is at room temperature, the highest is no more than 60 ° C, stirring is carried out during the reaction, and the rotating speed of the agitator is more suitable at 500 rpm; the reaction time is 2-15 minutes;

d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt salt powder.

(2) the step of preparing cobalt hydroxide:

a, prepare cobalt salt aqueous solution, cobalt salt is cobalt chloride or cobalt sulfate, and its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4- 1.2;

B, configuration NaOH solution, its concentration is 10-30% (weight ratio), and feeds ammoniacal liquor and makes precipitation agent, and its feeding amount is: NaOH (10-30%) and ammoniacal liquor (specific gravity=0.9-1.0) Volume ratio 5-10: 1; Also can add described dispersing agent in this solution, polyethylene glycol (molecular weight is 4000), or butadiene, or acrylic acid, or the mixture of butadiene and acrylic acid For the mixture, the amount of the dispersant added is 2-8 grams per 10 liters of NaOH solution aqueous solution.

c. Spray the precipitant aqueous solution in the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution in the precipitant aqueous solution, and the ratio of the cobalt salt and the material obtained in the b step meets the requirements of the equation for the reaction of the two substances During the reaction process, always keep the pH of the mixed solution stable at a certain value in 10-12, the optimal value is 10.8±0.1, and keep it constant by adjusting the feeding speed. , implement stirring in the reaction, the rotating speed of agitator is more suitable at 500 rpm; the reaction time is 2-3 hours;

d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt hydroxide powder.

(3) the step of preparing cobalt carbonate:

a, prepare cobalt salt aqueous solution, cobalt salt is cobalt chloride or cobalt sulfate, and its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4- 1.2;

B, configuration NH ₄ HCO ₃ solution, its concentration is 60-120 gram/liter, and feeds ammoniacal liquor and makes the pH of this precipitant be 7-9; Add described dispersant in this solution, polyethylene glycol (molecular weight 4000), or butadiene, or acrylic acid, or a mixture of butadiene and acrylic acid, the addition of the dispersant is to add 2-8 grams per 10 liters of the solution.

c. Spray the precipitant aqueous solution in the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution in the precipitant aqueous solution, and the ratio of the cobalt salt and the material obtained in the b step meets the requirements of the equation for the reaction of the two substances During the reaction process, keep the pH of the mixed solution stable at a certain value in the range of 7.5-8.5, the optimum value is 10.8±0.1, and keep it constant by adjusting the feeding speed. , implement stirring in the reaction, the rotating speed of agitator is more suitable at 500 rpm; the reaction time is 1-3 hours;

d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt carbonate powder.

The factors that determine the spherical shape of cobalt salt grains in the above-mentioned cobalt salt preparation process are:

Feeding method. In the two raw materials of the cobalt salt and the precipitant, it is all right to inject any one of them into another solution, but it is not suitable if the two solutions are injected into the container at the same time (i.e. offset feeding), because in this way There is a greater tendency to form needle-like grains.

Again, feed rate. Its size will affect the bulk density of the formed product. If the feeding speed is too high, the formed grains will be too small and the bulk density will be too small. If the feeding speed is too slow, the formed grains will be too large and the bulk density will be low. will be smaller.

Also add a dispersant. Adding the dispersant to the reactant can effectively prevent the formed grains from sticking to each other, which is beneficial to ensure the particle size and crystal form of the product.

Of course, the concentration of reactants, reaction temperature, reaction time, and pH in the crystallization process all have an impact on the size, uniformity, and bulk density of the crystal grains. The matching of each parameter in the above process can produce a spherical shape. Cobalt salt powder with suitable grain size.

In addition, when adding the precipitant, it should be noted that the amount of the dispersant should not be too much, otherwise, there will be excess dispersant remaining after the reaction, and the carbon content in the final product will be too large.

The preparation method of tricobalt tetroxide provided by the present invention changes the one-stage calcination and the same gas atmosphere generally used in the prior art into three-stage calcination, does not provide an oxidizing agent in the thermal decomposition of cobalt salt, so that it is all converted into cobaltous oxide first, and then Reheat to oxidation temperature and provide oxygen or air atmosphere. In the product prepared by the method, the conversion rate of tricobalt tetroxide is high, other oxides of cobalt are very few, and the particle size is uniform and the bulk density is large, which is beneficial to improving the electrical performance and service life of the battery. In addition, proper control of various operating parameters in the preparation of cobalt salt can obtain spherical cobalt salt particles, and the cobalt tetroxide obtained by calcining it as a raw material is more ideal in particle size and bulk density, wherein the Co content is 73-73.5%. The packing density is 2-2.4g/cm ³ , and the particle size is 3-5μm.

Description of drawings

The present invention will be further described below in conjunction with accompanying drawing.

Fig. 1 is the technological process schematic diagram of preparing spherical cobalt oxalate and carrying out three stages of calcination to it;

Fig. 2 is the cobalt oxalate powder of spherical shape, obtained through three-stage calcination of cobalt tetroxide powder 1 transmission electron microscope photo;

Fig. 3 is the transmission electron micrograph of the tricobalt tetroxide powder obtained by three-stage calcination using non-spherical cobalt oxalate;

Fig. 4 is the transmission electron micrograph of the tricobalt tetroxide powder 2 obtained by three-stage calcination of spherical cobalt carbonate;

Fig. 5 is a transmission electron micrograph of cobalt tetroxide powder 3 obtained by three-stage calcination of spherical cobalt hydroxide;

Fig. 6 is a comparative example, a transmission electron micrograph of the tricobalt tetroxide powder obtained by one-stage calcination;

Fig. 7 is an X-ray diffraction diagram using three groups of products 1, 2, 3 shown in Fig. 2, 4, 5 and standard cobalt tetroxide powder.

Detailed ways

Example 1:

Prepare tricobalt tetroxide with the processing method as shown in Figure 1, and its step is:

1. Preparation of spherical cobalt oxalate powder:

a. To prepare an aqueous solution of cobalt chloride, heat aqua regia (HCl:HNO ₃ =3:1) to 80-90°C, dissolve the electrolytic cobalt flakes in it, and form a cobalt chloride solution with a concentration of 100 g/L , and adding oxalic acid for acidification, so that the pH of the cobalt chloride aqueous solution is 0.6-0.8;

b. Preparation of ammonium oxalate aqueous solution: add NH ₃ into oxalic acid to make the concentration 90 g/L, and make the pH of ammonium oxalate aqueous solution 4.3-4.5; add dispersant to the ammonium oxalate solution, which is polyhexyl Alcohol (molecular weight is 4000), the addition amount of this dispersant is to add 6.25 grams in every 10 liters of ammonium oxalate aqueous solution.

c. Add the ammonium oxalate aqueous solution prepared in step b to the cobalt chloride aqueous solution prepared in step a by spraying, and add the ammonium oxalate in such an amount that the pH of the reaction solution reaches 1.0-1.5. The addition speed of cobalt oxalate is to make the pH value of reaction solution reach requirement in 5 minutes. The reaction temperature is controlled between 36-42° C., stirring is carried out during the reaction, and the rotation speed of the stirrer is 500 rpm; the reaction is continued for 2-3 minutes after the addition is completed.

d. After the reaction is completed, the above crystals are separated from the mother liquor, dehydrated and dried to obtain the spherical cobalt oxalate powder.

2. Preparation of cobalt tetroxide powder:

a. One-stage calcination:

Put the cobalt oxalate powder prepared in the above process into a calciner and heat it. The heating temperature is 300°C and the heating time is ³ hours. Residual moisture and crystal water in the salt powder are removed;

B. Two-stage calcination:

Heat the material treated in the previous dehydration step at a temperature of 500°C for 2 hours, the calcination equipment is still in a nitrogen atmosphere, and the flow rate of nitrogen is 5M ³ /min; in this process, more than 99% of oxalic acid Thermal cracking of cobalt into cobaltous oxide;

C. Three-stage calcination:

Heat the material treated in the previous step at a temperature of 750° C. for 3 hours. Air is introduced into the calcining equipment at a pressure of 980 kPa (1 Kg/cm ² ); Oxidized to Co ₃ O ₄ ;

Then, place the above Co ₃ O ₄ powder at room temperature to cool, and finally pack into finished products.

The heating time of each stage of calcination often depends on the stacking thickness of the material, in addition, it also depends on other specific conditions of the material, such as the heating time in one stage of calcination depends on the water content of the material and so on.

The crystal particles of Co ₃ O ₄ produced by the above process can be seen in the Co ₃ O ₄ powder transmission electron microscope photo shown in Figure 2, in which the Co ₃ O ₄ particles are spherical, with a Co content of 73.31 and a particle size of d ₅₀ =3.58 μm, and its bulk density is 2.18 g/cm ³ . Its powder color is blue-black, and the product number is 1. The transmission electron microscope photo of the powder is shown in Figure 2, and its X-ray diffraction pattern line is shown in Figure 7 as graph line 1.

Here is a comparative example:

It uses non-spherical cobalt oxalate powder, which is not controlled by nitrogen atmosphere, and is calcined in one stage with air ventilation, and the powder color of the obtained product is gray-black. Since the color of CoO is gray-green, the color of the above product indicates that there is some CoO that has not been oxidized into Co ₃ O ₄ , and its particle size is relatively large and uneven. The bulk density is 1.7g/cm ³ , which is relatively low. . Its transmission electron microscope photograph is shown in Fig. 6.

As shown in Figure 3, it is the transmission electron microscope photo of the product obtained after calcining in the same method as embodiment 1 of the present invention by adopting non-spherical cobalt oxalate, as can be clearly seen from the photo, the outline of the crystal grain of the product is It has a square shape, its Co content is 73.49, its particle size d ₅₀ =4.45 μm, and its bulk density is 1.60 g/cm ³ . The powder color is blue-black, which means that the content of cobalt tetroxide is extremely high. But its bulk density is lower than the corresponding physical property index of the quasi-spherical crystal grains prepared by the process provided by the present invention.

Example 2:

1. Preparation of spherical ammonium carbonate powder:

a, preparation of cobalt chloride aqueous solution, its concentration is 60 grams per liter, and adding sulfuric acid makes the pH of cobalt salt aqueous solution be 0.5-0.6;

b, prepare ammonium bicarbonate aqueous solution, its concentration is 70 g/liter, and pass into ammonia to make the pH of ammonium bicarbonate aqueous solution be 7-9; Add dispersant in ammonium bicarbonate solution, it is butadiene and acrylic acid The mixture, its ratio is: 1: 1, and the addition amount of this dispersant is every 10 liters of ammonium bicarbonate aqueous solution and adds 7 grams and gets final product.

c. Spray and add the ammonium bicarbonate aqueous solution in the cobalt salt aqueous solution until the pH of the mixed solution reaches 7.5-8.5, and keep the above pH constant during the reaction process. The method for maintaining the constant pH is to make the cobalt salt solution The add-on of constant, adjusts the add-on of ammonium bicarbonate to realize. The reaction temperature is at normal temperature, the highest is not more than 50° C., the stirring is carried out during the reaction, and the rotation speed of the stirrer is 500 rpm; the reaction time is 1-3 hours.

To prepare cobalt carbonate, the precipitation reaction can be a continuous process, wherein the feeding rate of the two materials is: cobalt chloride solution 30-60L/hr, and the adding rate of ammonium bicarbonate is matched by pH.

d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt carbonate powder.

2. Preparation of cobalt tetroxide powder:

a. One-stage calcination:

Put the cobalt carbonate powder prepared in the above process into a calciner and heat it, the heating temperature is 250°C, the heating time is 5 hours, the calciner is a nitrogen atmosphere, and the nitrogen flow rate is 3M ³ /min;

B. Two-stage calcination:

Heat the material treated in the previous dehydration step at a temperature of 500°C for 4 hours, and the calcination equipment is still in a nitrogen atmosphere, and the flow rate of nitrogen is 5M ³ /min;

C. Three-stage calcination:

Heating the material treated in the previous step at a temperature of 700°C for 8 hours, and introducing air into the calcining equipment; during this process, all cobaltous oxide is oxidized into tricobalt tetroxide;

Then, place the above-mentioned tricobalt tetroxide powder at room temperature to cool, and finally pack into finished products.

The Co ₃ O ₄ particles produced by the above process are spherical, with a Co content of 73.26, a particle size of d ₅₀ =4.50 μm, and a bulk density of 2.15 g/cm ³ . Its powder color is blue-black, and the serial number of this product is mixed 2, and the transmission electron microscope photograph of this powder is shown in Figure 4, and its X-ray diffraction pattern line is shown in Fig. 7 as graph line 2.

Example 3:

1. Preparation of spherical cobalt hydroxide powder:

A, preparation cobalt chloride aqueous solution, its concentration is 120 grams per liter, and adding hydrochloric acid makes the pH of aqueous solution be 0.9-1.1;

B, preparation contains the ammoniacal NaOH solution, and its concentration is 20%, and feeds the ammoniacal liquor that specific gravity d is 95%, the volume ratio of NaOH (20%) and ammoniacal liquor (specific gravity=0.95) is 8: 1; Add in this solution The dispersant is a mixture of butadiene and acrylic acid, the ratio of which is 1:1, and the amount of the dispersant is 7 grams per 10 liters of NaOH aqueous solution.

c. Spray the NaOH solution prepared in step b into the cobalt salt aqueous solution, and maintain the pH at 10-11, so that the reaction proceeds at a stable pH. The mode of maintaining pH is to stabilize the addition of cobalt chloride, and adjust the addition of NaON solution at any time. The reaction temperature is at normal temperature, the highest is not more than 60° C., the stirring is carried out during the reaction, and the rotation speed of the stirrer is 500 rpm; the reaction time is 2-3 hours.

To prepare cobalt hydroxide, the precipitation reaction can be a continuous process, wherein the feeding rate of the two materials is: cobalt chloride solution 50-70L/hr, and the adding rate of NaOH is matched by pH.

d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt hydroxide powder.

2. Preparation of cobalt tetroxide powder:

a. One-stage calcination:

Put the cobalt hydroxide powder prepared in the above process into a calcination equipment for heating, the heating temperature is 450°C, the heating time is 2 hours, the calcination equipment is a nitrogen atmosphere, and the nitrogen flow rate is 3M ³ /min;

B. Two-stage calcination:

Heat the material treated in the previous dehydration step at a temperature of 550°C for 4 hours, and the calcination equipment is still in a nitrogen atmosphere, and the flow rate of nitrogen is 5M ³ /min;

C. Three-stage calcination:

Heating the material treated in the previous step at a temperature of 900°C for 5 hours, and introducing air into the calcining equipment; during this process, all cobaltous oxide is oxidized into tricobalt tetroxide;

Then, place the above-mentioned tricobalt tetroxide powder at room temperature to cool, and finally pack into finished products.

The Co ₃ O ₄ particles produced by the above process are spherical, with a Co content of 73.26, a particle size of d ₅₀ =4.50 μm, and a bulk density of 2.15 g/cm ³ . Its powder body color is blue black, and the serial number of this product is 3, and the transmission electron microscope picture of this powder body is shown in Figure 5, and its X-ray diffraction pattern line is shown in Fig. 7 graph line 3.

As shown in Figure 4, the Co ₃ O ₄ product 1, product 2 and product 3 produced by calcining the spherical cobalt oxalate cobalt carbonate and cobalt hydroxide with the method of the present invention and the industry-recognized Co ₃ O _4. The X-ray diffraction pattern line of the standard sample, compared with the standard sample, the product prepared by the preparation method of the present invention has the same X-ray spectral line, which shows that this product has the same structure as the standard sample, that is, where Co ₃ O ₄ content is above 99%.

Claims (10)

1. A method for preparing cobalt tetroxide for lithium ion batteries, using cobalt oxalate, cobalt hydroxide or cobalt carbonate as raw materials, the particle size of the cobalt salt is D ₅₀ =2-8 μm; the preparation steps are: three-stage calcination of the above raw materials : A. One stage calcination: Put the cobalt salt powder in a calcination equipment to heat, the heating temperature is 200-450°C, the heating time is 2-5 hours, and the calcination equipment is a nitrogen atmosphere; the process is to make the remaining moisture and/or water in the cobalt salt powder or water of crystallization is removed; B. Two-stage calcination: Heat the material treated in the previous step at a temperature of 500-800°C for 1-5 hours, and the calcination equipment is still in a nitrogen atmosphere; during this process, the cobalt salt is thermally decomposed into cobaltous oxide; C. Three-stage calcination: Heat the material treated in the previous step at a temperature of 700-1000°C for 2-8 hours, and the calcining equipment is in an air or oxygen atmosphere; during this process, cobaltous oxide is oxidized to tricobalt tetroxide; Then, place the above-mentioned tricobalt tetroxide powder at room temperature to cool, and finally pack into finished products. 2. The preparation method of tricobalt tetroxide according to claim 1, characterized in that: in the method, the grain shape of the cobalt salt powder is spherical. 3. The preparation method of tricobalt tetroxide according to claim 2, characterized in that: the cobalt salt of spherical grains is cobalt oxalate, which comprises the following preparation steps: a, prepare cobalt salt aqueous solution, its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4-1.2; B, configuration cobalt oxalate solution, its concentration is 60-120 gram/liter, and the pH of passing into the described precipitation agent aqueous solution of ammonia is 3-5; c. Spray the ammonium oxalate precipitant aqueous solution into the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution into the ammonium oxalate precipitant aqueous solution, and the ratio of cobalt salt and ammonium oxalate meets the requirements of the equation for the reaction of the two substances The amount until the pH of the mixed solution reaches 1-1.5, the reaction temperature is at room temperature, the highest is not more than 60 ° C, stirring is carried out during the reaction, the speed of the stirrer is more suitable at 500 rpm; the reaction time is 2-15 minute; d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt salt powder. 4. The preparation method of tricobalt tetroxide according to claim 2, characterized in that: the cobalt salt of spherical grains is cobalt carbonate, which comprises the following preparation steps: a, prepare cobalt salt aqueous solution, cobalt salt is cobalt chloride or cobalt sulfate, and its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4- 1.2; B, configuration NH ₄ HCO ₃ solution, its concentration is 60-120 g/liter, and feeds ammoniacal liquor to make the pH of this precipitation agent be 7-9; c. Spray the precipitant aqueous solution in the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution in the precipitant aqueous solution, and the ratio of the cobalt salt and the material obtained in the b step meets the requirements of the equation for the reaction of the two substances During the reaction, the pH of the mixed solution is stable at 7.5-8.5, the reaction temperature is at room temperature, and the maximum does not exceed 60 ° C. Stirring is carried out during the reaction. The speed of the agitator is 500 rpm. It is more suitable; the reaction time is 1-3 Hour; d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt carbonate powder. 5. The preparation method of tricobalt tetroxide according to claim 2, characterized in that: the cobalt salt of spherical grains is cobalt hydroxide, which comprises the following preparation steps: a, preparation of cobalt salt aqueous solution, cobalt salt is cobalt chloride or cobalt sulfate, its concentration is 50-130 g/liter, and add one or more in hydrochloric acid or oxalic acid or sulfuric acid to make the pH of cobalt salt aqueous solution be 0.4- 1.2; B, configuration NaOH solution, its concentration is 10-30% (weight ratio), and feeds ammoniacal liquor and makes precipitation agent, and its feeding amount is: NaOH (10-30%) and ammoniacal liquor (specific gravity=0.9-1.0) Volume ratio 5-10:1; c. Spray the precipitant aqueous solution in the cobalt salt aqueous solution, or spray the cobalt salt aqueous solution in the precipitant aqueous solution, and the ratio of the cobalt salt and the material obtained in the b step meets the requirements of the equation for the reaction of the two substances During the reaction, the pH of the mixed solution is stabilized at a certain value in the range of 10-12 and kept constant. The reaction temperature is at room temperature, and the maximum does not exceed 60°C. Stirring is carried out during the reaction, and the speed of the stirrer is 500 rpm. Minutes are more appropriate; the reaction time is 2-3 hours; d. Separating the crystals produced by the above reaction from the mother liquor and drying to obtain the spherical cobalt hydroxide powder. 6. The preparation method of tricobalt tetroxide according to claim 1, characterized in that: the heating temperature of the one-stage calcination is 250-350°C. 7. The preparation method of tricobalt tetroxide according to claim 1, characterized in that: the heating temperature of the second-stage calcination is 550-650°C. 8. The preparation method of tricobalt tetroxide according to claim 1, characterized in that: the heating temperature of the three-stage calcination is 750-850°C. 9. The preparation method of tricobalt tetroxide according to claim 3, 4 or 5, characterized in that: a dispersant is added to the precipitating agent, which is polyethylene glycol (molecular weight: 4000), or butadiene , or acrylic acid, or a mixture of butadiene and acrylic acid, the amount of the dispersant added is 2-8 grams per 10 liters of precipitant aqueous solution. 10. The preparation method of tricobalt tetroxide according to claim 1, characterized in that: the amount of nitrogen gas introduced in the first-stage calcination or the second-stage calcination is 3-5M ³ /min

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