Preparation method and application of high-purity carbonic acid system large-particle cobaltosic oxide

Abstract

The invention provides a preparation method of high-purity carbonic acid system large-particle cobaltosic oxide, which comprises the following steps: firstly, adding a cobalt salt solution and an ammonium bicarbonate solution into a reaction container by adopting a one-time feeding mode, and reacting under the conditions of proper temperature and pH value and low-rotating-speed stirring to obtain a first product containing cobalt carbonate seed crystal; then, removing supernate, adding the cobalt salt solution and the ammonium bicarbonate solution into the reaction container in a parallel flow manner according to a certain flow ratio, and continuing to react, so as to obtain a second product containing cobalt carbonate; and finally, washing the cobalt carbonate particles for multiple times by using an ammonium bicarbonate solution, and then carrying out water washing, drying and calcining treatment to obtain the large-particle cobaltosic oxide. The prepared large-particle cobaltosic oxide of the carbonic acid system has the advantages of being good in dispersity, high in sphericity degree, high in purity and the like, preparation of a high-voltage and high-capacitance lithium cobalt oxide battery is facilitated, and the large-particle cobaltosic oxide has wide popularization and application prospects in lithium ion battery positive electrode materials.

Description

Technical Field

[0001] The invention relates to the technical field of lithium ion battery materials, and in particular to a method for preparing high-purity carbonate-based large-particle cobalt tetroxide, and also to application of the carbonate-based large-particle cobalt tetroxide in lithium ion battery positive electrode materials. Background Art

[0002] With the continuous development of economy and science and technology, the consumption of battery energy is increasing day by day. This change has promoted the continuous updating of electronic products, and lithium batteries used in electronic products are also emerging in an endless stream. Smartphones, tablets, drones and other products often use lithium batteries as their power source. Lithium cobalt oxide materials are increasingly widely used as positive electrode materials for lithium batteries due to their high operating voltage, stable charge and discharge structure, high specific energy, good cycle performance, and environmental friendliness. At present, all positive electrode material factories are committed to improving the charging cut-off voltage and capacity of lithium cobalt oxide materials. As a precursor of lithium cobalt oxide, the performance of cobalt oxide has a direct impact on the performance of lithium cobalt oxide materials, and has attracted more and more attention.

[0003] For cobalt tetroxide, its dispersibility, sphericity and purity are all important performance indicators. Among them, good dispersibility can make cobalt tetroxide evenly distributed in the electrode material, increase the contact area between the electrode and the electrolyte, improve the embedding and extraction efficiency of lithium ions, and thus improve the charge and discharge performance and rate performance of the battery. When making electrodes, cobalt tetroxide with high sphericity can be stacked more tightly, making the electrode material distribution more uniform, which is conducive to the embedding and extraction of lithium ions in the electrode, thereby improving the charge and discharge efficiency of the battery and enhancing the cycle stability. In addition, the contact area between particles with high sphericity is relatively small. During the battery charge and discharge cycle, it can reduce the agglomeration and mutual friction between particles, reduce the degree of pulverization of electrode materials, and thus enhance the cycle stability of the battery and extend the battery life. High-purity cobalt tetroxide can reduce the impurity content, reduce the battery self-discharge rate, and improve the storage performance and safety of the battery; at the same time, it can also make the prepared lithium cobalt oxide positive electrode material have a higher specific capacity, thereby improving the energy density and charge and discharge performance of the battery and extending the cycle life of the battery.

[0004] Based on this, it is a technical problem that needs to be solved urgently to provide a method for preparing large-particle cobalt tetroxide in a carbonate system with good dispersibility, high sphericity and high purity. Summary of the invention

[0005] One of the purposes of the present invention is to provide a method for preparing large-particle cobalt tetroxide in a carbonate system with good dispersibility, high sphericity and high purity.

[0006] The second object of the present invention is to provide a carbonate system large particle cobalt tetroxide with good dispersibility, high sphericity and high purity.

[0007] The third object of the present invention is to provide a high-purity carbonate system large-particle cobalt tetroxide for use in lithium-ion battery positive electrode materials.

[0008] The technical solution adopted by the present invention to achieve one of the purposes is: to provide a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system, comprising the following steps: S1. Prepare a cobalt salt solution with a cobalt ion concentration of 100-130 g / L and an ammonium bicarbonate solution with a concentration of 160-180 g / L respectively; S2, using a one-time feeding method, adding a cobalt salt solution and an ammonium bicarbonate solution to a reaction container containing a base liquid at a mass ratio of cobalt ions to ammonium bicarbonate of (1:1.2)-(1:4), reacting at 40-45° C., pH 7.1-7.8, and a stirring speed of 80-120 rpm to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3 μm; S3, stopping the kettle for sedimentation, removing the supernatant, heating again to 40-45° C., introducing the cobalt salt solution and the ammonium bicarbonate solution into the reaction vessel in a parallel flow manner at a flow ratio of (1:1.8)-(1:4), and continuing the reaction at a stirring speed of 300-500 rpm to obtain a second product containing cobalt carbonate; S4. Performing solid-liquid separation on the second product to obtain cobalt carbonate particles, washing the cobalt carbonate particles multiple times with an ammonium bicarbonate solution, and then washing with water, drying and calcining to obtain large particles of cobalt trioxide.

[0009] The overall idea of ​​the present invention is as follows: In order to prepare a large-particle cobalt tetraoxide in a carbonate system with good dispersibility, high sphericity and high purity, the present invention mainly makes the following improvements: First, a combination of one-time feeding and parallel feeding is adopted. In the seeding stage, a one-time feeding method (i.e., adding the cobalt salt solution and ammonium bicarbonate solution to the reaction vessel at one time) is adopted instead of peristaltic pump feeding. This method not only saves reaction time and improves production efficiency, but also helps the cobalt salt solution and ammonium bicarbonate solution to undergo homogeneous precipitation to generate cobalt carbonate particles with higher sphericity. In addition, controlling the stirring speed at 80-120rpm in the seeding stage can avoid the agglomeration of particles in the high-concentration reaction solution and improve the dispersibility of the product.

[0010] Secondly, when the particle size of the product grows to a certain size, the kettle is stopped for sedimentation, and after the supernatant is siphoned, the temperature is raised to 40-45°C again, and the growth stage is entered at this time. Studies have found that when the shutdown particle size is too large, it will cause the cobalt carbonate to contain more large-particle impurities; and if the shutdown particle size is too small, it will slow down the progress of the growth stage. Based on the above considerations, the present invention sets the shutdown particle size to a product particle size D50 of 10.8-11.3μm. In the growth stage, the prepared cobalt salt solution and ammonium bicarbonate solution are added to the reaction vessel in a parallel flow manner according to a certain flow ratio, and then the appropriate reaction temperature, system pH control and stirring speed are combined to control the slow and uniform growth of the particle size to obtain large-particle cobalt carbonate particles with higher sphericity.

[0011] Finally, the present invention uses an ammonium bicarbonate solution to wash the large cobalt carbonate particles multiple times. On the one hand, compared with directly using pure water to wash the product in conventional operations, the ammonium ions and carbonate ions in the ammonium bicarbonate solution used in the present invention can react chemically with the metal ion impurities attached during the preparation of the cobalt carbonate particles to form insoluble carbonates or basic carbonates, thereby effectively removing impurities and improving the purity of the cobalt carbonate; on the other hand, compared with other detergents, the decomposition products of ammonium bicarbonate are ammonia, carbon dioxide, and water, which are all environmentally friendly substances and will not pollute the environment. At the same time, the washed solution can be decomposed and processed by simple methods such as heating, and the subsequent processing cost is also low.

[0012] Furthermore, in step S1, the cobalt salt is selected from a combination of one or more of cobalt chloride, cobalt sulfate and cobalt nitrate.

[0013] Furthermore, in step S2, the base liquid is prepared by mixing the ammonium bicarbonate solution prepared in step S1 with water in a volume ratio of 1:(2-4).

[0014] Furthermore, in step S2, the cumulative reaction time is 18-22 hours.

[0015] Furthermore, in step S3, the cobalt salt solution and the ammonium bicarbonate solution are added into the reaction container in parallel through a peristaltic pump.

[0016] Preferably, in step S3, the flow rate of the cobalt salt solution is controlled to be 1.3-1.5 L / h. Studies have shown that, in the growth stage, if the flow rate of the raw material solution is too high, the self-repair efficiency of the cobalt carbonate particles will be reduced, thereby making the particle sphericity worse and causing non-spherical particles to exist.

[0017] Furthermore, in step S3, the stirring speed is controlled to be 300-500 rpm, which can prevent the stirring speed from being too fast to destroy the sphericity of the cobalt carbonate particles, and can also prevent the stirring speed from being too slow to cause particle agglomeration and adversely affect the dispersibility.

[0018] Further, in steps S2 and S3, the pH of the reaction system is controlled to be 7.1-7.8. It has been found that when the pH value is low, the hydrogen ion concentration in the solution is too high, which will inhibit the hydrolysis reaction of the cobalt ions, reduce the nucleation rate, generate a small number of particles but a large particle size, and due to the low surface charge density, the electrostatic repulsion between particles is small, and agglomeration is prone to occur, resulting in poor dispersibility. As the pH increases, the hydrolysis of cobalt ions is accelerated, the nucleation rate increases, the number of particles increases and the particle size becomes smaller, while the surface charge density increases, the electrostatic repulsion between particles is enhanced, and agglomeration can be effectively suppressed, so that dispersibility is improved. But when the pH is too high, there are too many hydroxides in the solution, resulting in the generation of basic salts, so that the purity of cobalt carbonate decreases. Preferably, in steps S2 and S3, the pH of the reaction system is controlled to be 7.2-7.5.

[0019] Furthermore, in steps S2 and S3, the reaction temperature is controlled within the range of 40-45° C. to avoid decomposition of ammonium bicarbonate in the system due to excessively high temperature. The released ammonia molecules are redissolved in water and ionized, increasing the hydroxide in the system, thereby generating partial basic salts, resulting in a decrease in the purity of cobalt carbonate.

[0020] Furthermore, in step S3, when the particle size growth rate gradually slows down, the feeding is stopped. After the reaction is complete, large-particle cobalt carbonate with a particle size D50 of 20.89-21.26 μm can be obtained. The cumulative reaction time of step S3 is 65-75 h.

[0021] Further, in step S4, the wet cobalt carbonate is first separated from the reaction container, and a Buchner funnel is used to perform suction filtration to achieve solid-liquid separation, and then washing and drying are performed. Preferably, the cobalt carbonate is washed with a centrifuge, and then the residual ammonium bicarbonate is removed by washing with pure water, and then the washed cobalt carbonate is dried by a flash evaporator, and the drying temperature is 100-130° C. and the time is 3-5 hours.

[0022] Further, in step S4, the concentration of ammonium bicarbonate used for washing is 40-43 g / L and the temperature is 30-35° C. Under the above conditions, if the number of washings is too small, impurities on the surface of the cobalt carbonate particles cannot be effectively removed, and if the number of washings is too large, the particles will partially dissolve and agglomerate, affecting the performance and dispersibility of the particles. Preferably, the number of washings in step S4 of the present invention is set to 10-13 times.

[0023] Further, in step S4, the calcination treatment includes: calcining the dried cobalt carbonate at 300-350°C for 2-3h, then heating to 400-500°C for 1-2h, and finally heating to 800-850°C for 5-7h. In the process of calcining cobalt carbonate of the present invention, a method of first calcining at low temperature, then transitioning to calcining at medium temperature, and finally calcining at high temperature is adopted. After calcining at low temperature and medium temperature, the surface of the particles is basically crystallized, which can effectively avoid excessive adhesion and agglomeration between particles during subsequent high temperature calcination, and is conducive to the formation of cobalt oxide particles with good dispersibility and uniform particle size.

[0024] The technical solution adopted by the present invention to achieve the second purpose is: to provide a high-purity large-particle cobalt tetroxide in a carbonate system, which is prepared by the preparation method according to one of the purposes of the present invention.

[0025] In some preferred embodiments, the particle size of the high-purity carbonate system large-particle cobaltous oxide is 17.26-17.93 μm.

[0026] The technical solution adopted by the present invention to achieve the third purpose is: to provide an application of the high-purity carbonate-based large-particle cobalt tetroxide described in the second purpose of the present invention in the positive electrode material of a lithium-ion battery.

[0027] The large-particle cobalt tetroxide in the carbonate system prepared by the present invention has the advantages of good dispersibility, high sphericity and high purity, and can better meet the preparation requirements of high-voltage and high-capacity lithium cobalt oxide batteries.

[0028] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention provides a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system. The method adopts a combination of one-time feeding and parallel feeding. The one-time feeding method is adopted in the seed stage, which saves reaction time and improves production efficiency. The one-time feeding helps the cobalt salt solution and the ammonium bicarbonate solution to undergo homogeneous precipitation to generate cobalt carbonate particles with higher sphericity. By reducing the stirring speed, the particles in the high-concentration reaction solution are prevented from agglomerating, thereby improving the dispersibility. In the growth stage, the flow rate, temperature, rotation speed, pH value and other conditions of the reaction solution are controlled to control the slow and uniform growth of the particle size to obtain large-particle cobalt carbonate particles with higher sphericity. In addition, the present invention uses ammonium bicarbonate solution to wash the large-particle cobalt carbonate particles multiple times to effectively remove impurities and improve the purity of cobalt carbonate and the final product. The preparation method provided by the present invention is simple to operate, time-saving and efficient, and easy to industrialize.

[0029] (2) The large-particle cobalt tetroxide in the carbonate system prepared by the present invention has the advantages of good dispersibility, high sphericity and high purity. The particle size D50 of the prepared cobalt tetroxide is 17.26-17.93 μm, which is conducive to the preparation of high-voltage and high-capacity lithium cobalt oxide batteries and has broad promotion and application prospects in lithium-ion battery positive electrode materials. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a SEM image of large-particle cobalt tetroxide in a carbonate system obtained in Example 1 of the present invention; Figure 2 Another SEM image of the large-particle cobalt tetroxide in the carbonate system obtained in Example 1 of the present invention; Figure 3 This is a particle size distribution diagram of the intermediate product cobalt carbonate particles obtained in Example 1 of the present invention; Figure 4 This is a particle size distribution diagram of large-particle cobalt tetroxide in the carbonate system prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0032] It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments may be combined with each other.

[0033] The embodiment of the present invention provides a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system, comprising the following steps: Step 1: preparing a cobalt salt solution with a cobalt ion concentration of 100-130 g / L and an ammonium bicarbonate solution with a concentration of 160-180 g / L respectively; the cobalt salt is selected from a combination of one or more of cobalt chloride, cobalt sulfate, and cobalt nitrate; Step 2: adding a base liquid to a reaction container, wherein the base liquid is prepared by mixing the ammonium bicarbonate solution prepared in step 1 with water in a volume ratio of 1:(2-4), and adding the cobalt salt solution and the ammonium bicarbonate solution to the reaction container containing the base liquid at a mass ratio of cobalt ions to ammonium bicarbonate of (1:1.2)-(1:4) in a one-time feeding manner, reacting for 18-22 hours at 40-45° C., pH 7.1-7.8, and a stirring speed of 80-120 rpm to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3 μm; Step 3: Stop the kettle for sedimentation, remove the supernatant by siphoning, heat up to 40-45° C. again, and pass the cobalt salt solution and the ammonium bicarbonate solution into the reaction container in a parallel flow manner at a flow ratio of (1:1.8)-(1:4) through a peristaltic pump, wherein the flow rate of the cobalt salt solution is controlled to be 1.3-1.5 L / h, and continue the reaction for 65-75 h at a stirring speed of 300-500 rpm to obtain a second product containing cobalt carbonate, wherein the particle size D50 of the cobalt carbonate in the second product is 20.89-21.26 μm; Step 4: Separate the wet cobalt carbonate from the reaction vessel, use a Buchner funnel to filter and separate the solid and liquid, and then wash and dry. The cobalt carbonate is washed with a centrifuge, the washing solution is an ammonium bicarbonate solution with a concentration of 40-43g / L, the washing temperature is 30-35°C, and the number of washings is 10-13 times; then wash with water, and then use a flash evaporator to dry the washed cobalt carbonate, the drying temperature is 100-130°C, and the time is 3-5h; finally, the dried cobalt carbonate is first calcined at 300-350°C for 2-3h, then heated to 400-500°C for 1-2h, and finally heated to 800-850°C for 5-7h, and finally large particles of cobalt tetroxide are obtained.

[0034] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited thereto.

[0035] Example 1 This embodiment provides a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system, comprising the following steps: Step 1: prepare a cobalt salt solution with a cobalt ion concentration of 110 g / L and an ammonium bicarbonate solution with a concentration of 170 g / L respectively; the cobalt salt is cobalt chloride; Step 2: Add a base liquid into a reaction container, wherein the base liquid is a mixture of 6L of deionized water and 2L of the ammonium bicarbonate solution prepared in step 1; add 4L of the cobalt salt solution and 3.11L of the ammonium bicarbonate solution (the mass ratio of cobalt ions to ammonium bicarbonate is 1:1.2) into the reaction container containing the base liquid at the same time by a one-time feeding method, react for 20 hours at 40° C., pH 7.2±0.1, and a stirring speed of 80 rpm to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3 μm; Step 3: Stop the kettle for sedimentation, remove the supernatant by siphoning, heat up to 40°C again, and pass the cobalt salt solution and ammonium bicarbonate solution prepared in step 1 into the reaction vessel in a parallel flow manner at a flow ratio of 1:1.8 through a peristaltic pump (wherein the flow rate of the cobalt salt solution is 1.5 L / h, and the flow rate of the ammonium bicarbonate solution is 2.7 L / h), and continue the reaction under the condition of a stirring speed of 300 rpm, so that the particle size of the cobalt carbonate particles gradually increases. When the particle size growth rate gradually slows down, stop feeding. After the reaction is complete, a second product containing large particles of cobalt carbonate is obtained. The cumulative reaction time of step 3 is 68 hours; Step 4: Separate the wet cobalt carbonate from the reaction vessel, use a Buchner funnel to filter and separate the solid and liquid, and then wash and dry. The cobalt carbonate is washed with a centrifuge, and the washing solution is an ammonium bicarbonate solution with a concentration of 40g / L, the washing temperature is 30°C, and the number of washings is 12 times; then wash with water, and then use a flash evaporator to dry the washed cobalt carbonate, the drying temperature is 100°C, and the time is 3h; finally, the dried cobalt carbonate is first calcined at 300°C for 2h, then heated to 400°C for 2h, and finally heated to 800°C for 6h, and finally large particles of cobalt tetroxide are obtained.

[0036] Figure 1 and 2 This is a SEM image of the large particles of cobalt tetraoxide in the carbonate system obtained in Example 1 of the present invention. Figure 1 and 2 It can be seen that the final product cobalt oxide prepared in the present invention has very good sphericity and dispersibility, no non-spherical particles and quasi-spherical particles exist, and no agglomeration occurs.

[0037] Further, according to Figure 3 and Figure 4 It can be seen from the particle size distribution diagram that the particle size D50 of the intermediate product cobalt carbonate particles obtained in Example 1 is 21.259 μm, and the particle size D50 of the final product carbonate system large particle cobalt tetroxide is 17.927 μm.

[0038] Example 2 This embodiment provides a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system, comprising the following steps: Step 1: prepare a cobalt salt solution with a cobalt ion concentration of 100 g / L and an ammonium bicarbonate solution with a concentration of 160 g / L respectively; the cobalt salt is cobalt chloride; Step 2: Add a base liquid into a reaction container, wherein the base liquid is a mixture of 6L of deionized water and 2L of the ammonium bicarbonate solution prepared in step 1; add 2L of the cobalt salt solution and 2.5L of the ammonium bicarbonate solution (the mass ratio of cobalt ions to ammonium bicarbonate is 1:2) into the reaction container containing the base liquid at the same time by a one-time feeding method, react at 42° C., pH 7.3±0.1, and a stirring speed of 100 rpm for 21 hours to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3 μm; Step 3: Stop the kettle for sedimentation, remove the supernatant by siphoning, heat up to 42°C again, and pass the cobalt salt solution and ammonium bicarbonate solution prepared in step 1 into the reaction vessel in a parallel flow manner at a flow ratio of 1:2.1 through a peristaltic pump (wherein the flow rate of the cobalt salt solution is 1.5 L / h, and the flow rate of the ammonium bicarbonate solution is 3.15 L / h), and continue the reaction under the condition of a stirring speed of 400 rpm, so that the particle size of the cobalt carbonate particles gradually increases. When the particle size growth rate gradually slows down, stop feeding. After the reaction is complete, a second product containing large particles of cobalt carbonate is obtained. The cumulative reaction time of step 3 is 70 hours; Step 4: Separate the wet cobalt carbonate from the reaction vessel, use a Buchner funnel to filter and separate the solid and liquid, and then wash and dry. The cobalt carbonate is washed with a centrifuge, and the washing solution is an ammonium bicarbonate solution with a concentration of 42g / L, the washing temperature is 32°C, and the number of washings is 13 times; then wash with water, and then use a flash evaporator to dry the washed cobalt carbonate, the drying temperature is 110°C, and the time is 5h; finally, the dried cobalt carbonate is first calcined at 350°C for 2h, then heated to 450°C for 1h, and finally heated to 850°C for 7h, and finally large particles of cobalt tetroxide are obtained.

[0039] The intermediate cobalt carbonate particles and the final cobalt oxide prepared in this example both have very good sphericity and dispersibility, and there are no non-spherical particles or quasi-spherical particles, and no agglomeration occurs.

[0040] After testing, the particle size D50 of the intermediate product cobalt carbonate particles obtained in Example 2 is 20.89 μm, and the particle size D50 of the final product carbonate system large particle cobalt tetroxide is 17.26 μm.

[0041] Example 3 This embodiment provides a method for preparing large-particle cobalt tetroxide in a high-purity carbonate system, comprising the following steps: Step 1: prepare a cobalt salt solution with a cobalt ion concentration of 130 g / L and an ammonium bicarbonate solution with a concentration of 180 g / L respectively; the cobalt salt is cobalt chloride; Step 2: Add a base liquid into a reaction container, wherein the base liquid is a mixture of 6L of deionized water and 2L of the ammonium bicarbonate solution prepared in step 1; add 5L of the cobalt salt solution and 8.31L of the ammonium bicarbonate solution (the mass ratio of cobalt ions to ammonium bicarbonate is 1:2.3) into the reaction container containing the base liquid at the same time by a one-time feeding method, react at 45°C, pH 7.5±0.1, and stirring speed 120rpm for 20.5h to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3μm; Step 3: Stop the kettle for sedimentation, remove the supernatant by siphoning, heat up to 45°C again, and pass the cobalt salt solution and ammonium bicarbonate solution prepared in step 1 into the reaction vessel in a parallel flow manner at a flow ratio of 1:3.2 through a peristaltic pump (wherein the flow rate of the cobalt salt solution is 1.3 L / h, and the flow rate of the ammonium bicarbonate solution is 4.16 L / h), and continue the reaction at a stirring speed of 450 rpm, so that the particle size of the cobalt carbonate particles gradually increases. When the particle size growth rate gradually slows down, stop feeding. After the reaction is complete, a second product containing large particles of cobalt carbonate is obtained. The cumulative reaction time of step 3 is 71 hours; Step 4: Separate the wet cobalt carbonate from the reaction vessel, use a Buchner funnel to filter and separate the solid and liquid, and then wash and dry. The cobalt carbonate is washed with a centrifuge, and the washing solution is an ammonium bicarbonate solution with a concentration of 43g / L, the washing temperature is 35°C, and the number of washings is 10 times; then wash with water, and then use a flash evaporator to dry the washed cobalt carbonate, the drying temperature is 130°C, and the time is 4h; finally, the dried cobalt carbonate is first calcined at 300°C for 3h, then heated to 500°C for 1h, and finally heated to 800°C for 5h, and finally large particles of cobalt tetroxide are obtained.

[0042] The intermediate cobalt carbonate particles and the final cobalt oxide prepared in this example both have very good sphericity and dispersibility, and there are no non-spherical particles or quasi-spherical particles, and no agglomeration occurs.

[0043] After testing, the particle size D50 of the intermediate product cobalt carbonate particles obtained in Example 3 was 21.05 μm, and the particle size D50 of the final product carbonate system large particle cobalt tetroxide was 17.62 μm.

[0044] Comparative Example The difference between this comparative example and Example 1 is that in the washing process of step 4, pure water is directly used to wash the cobalt carbonate without using an ammonium bicarbonate solution. The remaining steps and operations remain unchanged.

[0045] After testing, the purity of the intermediate product cobalt carbonate obtained in the comparative example is 99.21%, while in Example 1, the cobalt carbonate is washed multiple times with an ammonium bicarbonate solution before washing with water and then washed with water, and the purity of the intermediate product cobalt carbonate obtained can reach 99.85%.

[0046] The above are only preferred embodiments of the present invention, and are not intended to limit the implementation methods and protection scope of the present invention. Those skilled in the art should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing high-purity large-particle cobalt tetroxide in a carbonate system, characterized in that: The following steps are involved: S1. Prepare a cobalt salt solution with a cobalt ion concentration of 100-130 g / L and an ammonium bicarbonate solution with a concentration of 160-180 g / L respectively; S2, using a one-time feeding method, adding a cobalt salt solution and an ammonium bicarbonate solution to a reaction container containing a base liquid at a mass ratio of cobalt ions to ammonium bicarbonate of (1:1.2)-(1:4), reacting at 40-45° C., pH 7.1-7.8, and a stirring speed of 80-120 rpm to obtain a first product containing cobalt carbonate seeds, wherein the particle size D50 of the cobalt carbonate seeds is 10.8-11.3 μm; S3, stopping the kettle for sedimentation, removing the supernatant, heating again to 40-45° C., introducing the cobalt salt solution and the ammonium bicarbonate solution into the reaction vessel in a parallel flow manner at a flow ratio of (1:1.8)-(1:4), and continuing the reaction at a stirring speed of 300-500 rpm to obtain a second product containing cobalt carbonate; S4, performing solid-liquid separation on the second product to obtain cobalt carbonate particles; washing the cobalt carbonate particles multiple times with an ammonium bicarbonate solution, and then washing with water, drying and calcining to obtain large particles of cobalt trioxide.

2. The preparation method according to claim 1, characterized in that: In step S1, the cobalt salt is selected from a combination of one or more of cobalt chloride, cobalt sulfate and cobalt nitrate.

3. The preparation method according to claim 1, characterized in that: In step S2, the base liquid is prepared by mixing the ammonium bicarbonate solution and water in a volume ratio of 1:(2-4).

4. The preparation method according to claim 1, characterized in that: The reaction time of step S2 is 18-22 hours, and the reaction time of step S3 is 65-75 hours.

5. The preparation method according to claim 1, characterized in that: In step S3, the particle size D50 of cobalt carbonate in the second product is 20.89-21.26 μm.

6. The preparation method according to claim 1, characterized in that: In step S4, the concentration of the ammonium bicarbonate solution used for washing is 40-43 g / L, the temperature is 30-35° C., and the number of washing times is 10-13 times.

7. The preparation method according to claim 1, characterized in that: In step S4, the drying is performed by a flash evaporator at a temperature of 100-130° C. for 3-5 hours.

8. The preparation method according to claim 1, characterized in that: In step S4, the calcination treatment includes: calcining the dried cobalt carbonate at 300-350°C for 2-3h, then heating it to 400-500°C for 1-2h, and finally heating it to 800-850°C for 5-7h.

9. A high-purity carbonic acid system large particle cobalt tetroxide, characterized in that: It is prepared by the preparation method according to any one of claims 1 to 8; the particle size of the high-purity carbonate system large-particle cobalt tetroxide is 17.26-17.93 μm.

10. Use of the high-purity carbonate-based large-particle cobalt tetroxide according to claim 9 in positive electrode materials for lithium-ion batteries.

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