A method for preparing a scale-like cobaltosic oxide precursor

Abstract

The present application relates to the technical field of lithium ion battery cathode material precursor preparation, and particularly relates to a preparation method of flaky tricobalt tetroxide precursor, which solves the problems of poor sphericity and easy cracking of large-particle-size tricobalt tetroxide precursor. The method comprises: preparing an ammonium bicarbonate solution and an aluminum-cobalt salt-containing mixed solution, and performing a staged co-precipitation reaction in a reaction kettle; first, a nucleation reaction is performed at a specific pH and stirring speed to generate a spherical cobalt carbonate core; then, a shell forming reaction is performed, the reaction temperature is increased and the stirring speed is reduced when the D50 reaches a preset value, so as to promote the formation of a dense shell layer on the primary particles and uniformly coat the aluminum element. The present application precisely controls the temperature field and fluid field of the reaction stage, so that the surface of the precursor presents a flaky structure, effectively inhibits the particle cracking during the calcination process, and significantly improves the sphericity and structural compactness of the product.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode material precursor preparation technology, specifically to a method for preparing a flake-like cobalt tetroxide precursor. Background Technology

[0002] With the rapid development of lithium-ion battery technology, the market has placed higher demands on the energy density, cycle life, and safety performance of cathode materials. Cobalt tetroxide, as a key precursor for lithium cobalt oxide cathode materials, directly determines the electrochemical characteristics of the final cathode material due to its physicochemical properties. Especially with the expansion of high-voltage, high-capacity battery applications, the demand for cobalt tetroxide precursors with large particle size, high density, and controllable morphology is becoming increasingly urgent. In the preparation of cobalt tetroxide, the particle morphology, particle size distribution, and internal structural integrity of the precursor cobalt carbonate are core factors determining the performance of the final product. How to obtain a precursor with excellent sphericity and dense, crack-free particles through process control has become a focus of attention for those skilled in the art.

[0003] Currently, the mainstream industrial production technology for cobalt tetroxide is the wet co-precipitation-calcination method. This process typically uses cobalt salt solution and a precipitant (such as ammonium bicarbonate) as raw materials, and carries out a liquid-phase precipitation reaction in a reactor to generate a cobalt carbonate intermediate, which is then dehydrated and decomposed at high temperature to obtain cobalt tetroxide. A typical preparation scheme in existing technologies uses a continuous precipitation method with constant process parameters, i.e., maintaining a constant pH value, constant stirring speed, and constant reaction temperature during the reaction. Although this method is simple and easy to control, it has significant structural defects when preparing large-particle-size products. Because the reaction process does not differentiate and control the different stages of crystal growth, the crystal nucleation and crystal growth rates become unbalanced, and the generated cobalt carbonate particles often consist of disordered primary particles with a loose internal structure. This loose structure makes the particles prone to cracking or breakage during subsequent calcination due to uneven release of internal stress, seriously affecting the tap density and electrochemical performance of the product.

[0004] To improve particle morphology, another common approach in existing technologies is to optimize the precursor structure through doping modification. For example, dopants such as aluminum and magnesium are introduced into the reaction system, attempting to strengthen the particle structure through lattice substitution of heteroatoms or grain boundary pinning. However, existing doping processes typically employ a simple co-current feeding method, continuously adding a mixture of dopant salt solution and cobalt salt solution to the reactor. This simple doping method struggles to achieve a uniform distribution of dopants within the precursor particles, often resulting in dopant enrichment on the particle surface or the formation of local segregation. When the dopant distribution is uneven, it not only fails to provide the expected structural support but also causes stress concentration during calcination due to differences in local thermal expansion coefficients, exacerbating particle cracking. Furthermore, this surface enrichment leads to uneven distribution of active sites on the precursor surface, affecting the surface morphology of the subsequent calcined product and hindering the formation of a regular, scaly microstructure.

[0005] In summary, existing technologies for preparing large-particle-size cobalt tetroxide precursors generally suffer from problems such as poor sphericity due to limited reaction process control methods, loose internal particle structure prone to cracking, and performance degradation due to uneven distribution of dopant elements. Therefore, there is an urgent need for a preparation method that can precisely control the crystal growth process, optimize the internal stress distribution of particles, and achieve uniform embedding of dopant elements to solve the technical challenges of poor sphericity and easy cracking in large-particle-size cobalt tetroxide precursors. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a flake-like cobalt tetroxide precursor. This method achieves precise control of the cobalt carbonate crystal growth process by controlling the process parameters in stages, especially by differentiating the temperature, pH value and stirring intensity in the nucleation and shell-forming stages, thereby preparing a cobalt tetroxide precursor with a dense shell and a flake-like morphology on the surface.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing a flake-like cobalt tetroxide precursor includes the following steps: Step 1: Prepare ammonium bicarbonate solution A and ammonium bicarbonate solution B. Add ammonium bicarbonate solution A to the reaction vessel as the base solution. Step 2: Add aluminum salt to the cobalt salt solution to prepare a cobalt salt mixed solution. Add the cobalt salt mixed solution and ammonium bicarbonate solution B in parallel to the reactor to carry out the first stage of nucleation reaction and generate spherical cobalt carbonate nuclei. The conditions for the nucleation reaction in the first stage are as follows: the pH value of the reaction system is 8.0~8.8, the stirring speed is 300~400 r / min, the reaction time is controlled at 0~30h, the stirring speed is 400~500 r / min, and the reaction time is controlled at 30h until D50 reaches 18μm, the stirring speed is adjusted to 300~400 r / min. Step 3: Continue to introduce the cobalt salt mixed solution and ammonium bicarbonate solution B into the reactor to carry out the second stage of shell-forming reaction. During the shell-forming reaction, the reaction temperature is increased and the stirring speed is decreased, so that the primary particles grow on the surface of the spherical cobalt carbonate core to form a dense shell. After the reaction reaches the target particle size, the cobalt carbonate precursor is obtained by solid-liquid separation. The conditions for the shell-forming reaction in the second stage are as follows: the pH value of the reaction system is 7.2~8.1, the stirring speed is 50~200 r / min; when the D50 reaches 18~20 μm, the reaction temperature is raised to 45~60℃ and maintained for 10~30 h. Step 4: The second stage of the shell-forming reaction continues until the D50 reaches 20~22μm, at which point the feed is stopped, and 1~4 separate reactor operations are performed during this period; the cobalt carbonate precursor is calcined to obtain flake-like cobalt tetroxide. Further, the concentration of the ammonium bicarbonate solution A is 15~27g / L, the temperature is 30~40℃, and the pH value is 8~10; the concentration of the ammonium bicarbonate solution B is 150~300g / L, the temperature is 20~30℃, and the pH value is 8~10.

[0008] Furthermore, the cobalt salt solution is one or a mixture of cobalt chloride solution, cobalt sulfate solution, and cobalt nitrate solution, wherein the cobalt content in the cobalt salt solution is 100~180g / L, the temperature is 20~30℃, and the pH value is 1~3.

[0009] Furthermore, the aluminum salt is one or a mixture of aluminum sulfate, aluminum chloride, and aluminum nitrate, and the amount of aluminum salt added is 0.5-3% of the cobalt content in the cobalt salt solution.

[0010] Furthermore, in both the first and second stages of the reaction, the molar ratio of ammonium bicarbonate solution B to the cobalt salt mixture is 3.5 to 4.5.

[0011] Furthermore, the temperature of the first stage nucleation reaction is 35~45℃, the dense shell is formed by the close arrangement of small pyramidal primary particles, and the aluminum element in the aluminum salt is uniformly embedded inside the shell.

[0012] Compared with the prior art, the present invention has the following beneficial effects: (1) Because the present invention adopts a staged co-precipitation reaction process, especially by clearly dividing the reaction process into a nucleation stage and a shell-forming stage, and by setting the pH value and stirring speed differently according to the characteristics of different stages, the nucleation and growth processes of crystals are decoupled and controlled. Compared with the existing technology that uses constant parameters, resulting in disordered crystal growth and loose internal structure, the method of the present invention can precisely control the growth path of crystals, first forming a spherical nucleus and then growing a dense shell, thereby significantly improving the sphericity and tap density of the final product.

[0013] (2) By increasing the reaction temperature to 45–60 °C and decreasing the stirring speed to 50–200 r / min during the shell-forming stage (i.e., when D50 reaches 18–20 μm), a fundamental transformation of the crystal microstructure was achieved. The high temperature promoted crystal growth and densification, while the low shear force provided a mild environment for the orderly arrangement of primary particles. This measure enabled the primary particles to form a small pyramidal structure and be tightly packed, constructing a high-strength, dense shell, effectively solving the problem of particle cracking caused by the release of internal stress during the subsequent calcination of large-diameter precursors.

[0014] (3) Because the present invention introduces a specific proportion (0.5-3%) of aluminum salt into the cobalt salt solution and uses a staged feeding method, the aluminum element can be uniformly embedded in the cobalt carbonate lattice. Especially in the shell-forming stage, the aluminum element is effectively coated inside the dense shell layer. Compared with the prior art where dopants tend to accumulate on the surface or have uneven distribution, the aluminum distribution in the precursor prepared by the present invention is more uniform. This not only promotes the formation of a flake-like surface morphology, but also effectively inhibits grain coarsening and caking during calcination, thereby improving the electrochemical activity of the material.

[0015] (4) By controlling the molar ratio of ammonium bicarbonate solution B to cobalt salt mixture between 3.5 and 4.5, and in conjunction with a specific pH range, this invention establishes a suitable complexation equilibrium in the reaction system. The presence of ammonium ions plays an important role in complexation, controlling the release rate of cobalt ions, avoiding explosive nucleation, and thus ensuring the uniformity of particle size distribution. At the same time, this parameter setting also effectively reduces the generation of by-products and improves the utilization rate of raw materials. Attached Figure Description

[0016] Figure 1 This is a microscope image of product A of the present invention.

[0017] Figure 2 This is a microscope image of product D of the present invention. Detailed Implementation

[0018] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0019] This embodiment addresses the technical bottlenecks in the existing preparation of large-particle cobalt tetroxide precursors, such as poor sphericity, easy cracking of particles, and uneven distribution of doping elements. It proposes a new method for preparing flake-like cobalt tetroxide precursors through staged parameter control and the synergistic effect of aluminum doping.

[0020] This embodiment provides a method for preparing a flake-like cobalt tetroxide precursor, which includes the following steps: a base solution preparation step, a nucleation reaction step, a shell-forming reaction step, and a calcination step.

[0021] In the base solution preparation step, a specific concentration of ammonium bicarbonate solution is prepared as the reaction substrate environment. In the nucleation reaction step, a mixed solution containing aluminum cobalt salt and a precipitant are added in parallel flow, generating spherical cobalt carbonate nuclei under high pH and high stirring speed conditions. In the shell-forming reaction step, crystal growth is induced to form a dense shell by lowering the pH, increasing the temperature, and significantly reducing the stirring speed. Finally, in the calcination step, the final product is obtained through gradient temperature heat treatment. The design logic of the entire process is to decouple and control the crystal nucleation and growth processes, utilizing the synergistic effect of the hydrodynamic field and the thermodynamic field to achieve precise control of the microstructure.

[0022] Regarding the preparation of the base solution: This step is fundamental to the co-precipitation reaction. The ammonium bicarbonate solution A is added to the reaction vessel as the base solution, with a concentration controlled between 15 and 27 g / L, preferably 20 g / L. The selection of this concentration range is crucial: if the concentration is too low (<15 g / L), the concentration of ammonium ions in the solution is insufficient to form an effective buffer system, leading to drastic pH fluctuations in the initial stage of the reaction and difficulty in controlling the crystal nucleation rate; if the concentration is too high (>27 g / L), it will result in excessively high solution viscosity, affecting the subsequent stirring and mixing efficiency. The temperature of the base solution is controlled between 30 and 40°C, preferably 35°C. This temperature range ensures the solubility stability of ammonium bicarbonate, preventing low-temperature crystallization, and also avoids high-temperature decomposition and ammonia volatilization. The pH of the base solution is adjusted to 8 to 10, preferably 9.0, by adding ammonia or dilute nitric acid dropwise for fine adjustment. This weakly alkaline environment provides a suitable initial chemical potential for the subsequent precipitation of cobalt ions, avoiding boiling over or excessive fine powder due to excessive local supersaturation in the initial stage of the reaction.

[0023] Regarding the nucleation reaction step: This step constructs a nucleus with good sphericity. The cobalt salt mixed solution is prepared by adding aluminum salt to the cobalt salt solution. The cobalt salt solution is preferably a cobalt chloride solution, with a cobalt content controlled at 100–180 g / L, preferably 140 g / L. Cobalt chloride is chosen because of its high solubility, relatively low price, and the fact that chloride ions do not participate in the precipitation reaction in the reaction system and are easily removed by water washing. The solution temperature is maintained at 20–30°C, and the pH value is 1–3, exhibiting weak acidity. This is to prevent hydrolysis and precipitation of cobalt and aluminum ions in the storage tank. The aluminum salt is preferably an aluminum sulfate solution, with the amount added being 0.5–3% of the cobalt content, preferably 1.5%. The introduction of aluminum acts as a lattice regulator, because Al… 3+ Radius (0.0535nm) and Co 2+ The difference in radius (0.074nm) can cause lattice distortion after doping into the crystal lattice, which can change the growth habit of the crystal and promote the formation of plate-like or pyramidal primary particles.

[0024] In the nucleation stage, a cobalt salt mixed solution and ammonium bicarbonate solution B are added to the reactor in a parallel flow. The concentration of ammonium bicarbonate solution B is much higher than that of the base solution, controlled at 150–300 g / L, preferably 200 g / L. This high concentration of precipitant provides a sufficient source of carbonate ions, maintaining the supersaturation of the reaction system. The parallel flow is controlled by a precision metering pump, and the molar ratio of ammonium bicarbonate solution B to the cobalt salt mixed solution is controlled at 3.5–4.5, preferably 4.0. This molar ratio is slightly higher than the stoichiometric ratio, aiming to ensure complete precipitation of cobalt ions while utilizing excess ammonium ions to form a cobalt-ammonia complex, thus regulating the precipitation reaction rate.

[0025] Controlling the process parameters during the nucleation stage is crucial. The reaction time from 0 to 30 hours is defined as the nucleus generation and initial growth stage. During this stage, the reaction temperature is controlled at 35–45°C, preferably 40°C. The stirring speed is set to 400–500 r / min, preferably 450 r / min. The high stirring speed is designed to provide strong fluid shear force in the early stages of the reaction, allowing the reactants to disperse rapidly and uniformly, avoiding excessively high local concentrations that could lead to nucleus agglomeration. Simultaneously, the high shear force also helps to break up and disperse the generated fine nuclei, forming a large number of uniform seed crystals, providing a foundation for subsequent growth. At this time, the pH of the system is maintained at 8.0–8.8, preferably 8.4. Under this pH condition, the solution has a high degree of supersaturation, resulting in a faster nucleation rate. The generated cobalt carbonate primary particles are small dots, randomly stacked to form spherical cobalt carbonate nuclei. Although this disordered stacking structure is internally loose, it provides a large specific surface area and active sites for subsequent densification growth.

[0026] As the reaction progresses, when the reaction time exceeds 30 hours and the D50 particle size reaches 18–20 μm, a critical switch in process parameters is required. At this point, the reaction enters the transition stage from nucleation to shell formation. The stirring speed is reduced to 300–400 r / min, preferably 350 r / min. The purpose of reducing the speed is to decrease the fluid shear force, prevent the already formed larger particles from colliding and breaking during vigorous stirring, and simultaneously create a relatively stable fluid environment for the orderly growth of crystals. During this stage, the pH value is maintained at 8.0–8.8, and the reaction temperature is maintained at 35–45℃ to ensure continuous crystal growth.

[0027] Regarding the shell-forming reaction step: This step directly determines the density and surface morphology of the final product. When the D50 particle size reaches 18–20 μm, the shell-forming stage officially begins. At this point, a crucial "heating and deceleration" operation is required.

[0028] First, the reaction temperature is increased from 35–45℃ to 45–60℃, preferably 55℃. According to the principles of crystallization kinetics, increased temperature increases the kinetic energy of solute molecules, improves the diffusion coefficient, and makes it easier for ions to migrate to low-energy positions on the crystal surface and align, thereby promoting crystal growth and densification. Simultaneously, high temperature helps eliminate lattice defects within the crystal, increasing crystallinity. More importantly, in the presence of aluminum doping, high temperature promotes the solid solution of aluminum in the lattice, enhancing lattice strength.

[0029] Secondly, the stirring speed is significantly reduced to 50–200 r / min, preferably 100 r / min. This parameter setting breaks with conventional thinking. It is generally believed that high speed is required for the suspension of large particles, but this invention does the opposite. The technical logic is that the low speed creates a laminar or transitional flow fluid environment, which greatly reduces the scouring and shearing of the particle surface by the fluid. In this mild environment, the primary particles are no longer broken up and piled up, but are arranged in an orderly manner along the preferred growth direction of the crystal lattice. Combined with the pH value being reduced to 7.2–8.1 (preferably 7.6), the supersaturation of the solution is reduced, the nucleation tendency is suppressed, and the crystal growth tendency is enhanced. Under the dual effects of low supersaturation and low shear force, the primary particles grow into small pyramidal primary particles 21 with specific geometric shapes, and are closely arranged on the surface of the spherical cobalt carbonate nucleus 10, forming a dense shell 20. This dense shell 20 uniformly coats the aluminum element inside, preventing the precipitation of aluminum and surface caking during subsequent calcination.

[0030] The shell-forming stage typically lasts 10–30 hours until the D50 particle size reaches the preset 20–22 μm. During this period, 1–4 separate-reactor operations are required to control the solid content and particle size distribution. Separation refers to removing a portion of the liquid (a suspension containing solids) from the reactor to an aging reactor or centrifuge. Separation reduces the solid content in the reactor, decreases the probability of particle collisions, prevents particle agglomeration and growth, and ensures uniform particle size distribution.

[0031] After the reaction is complete, the slurry is sent to a centrifuge for solid-liquid separation and washed with pure water until the conductivity is qualified to remove residual chloride ions, ammonium ions and sulfate ions, and obtain cobalt carbonate precursor filter cake.

[0032] Regarding the calcination process: The cobalt carbonate precursor filter cake is fed into a rotary kiln for calcination. The calcination temperature is 750℃, during which the crystal transformation and lattice reconstruction are completed, forming cobalt tetroxide. The total sintering time is controlled within 2–4 hours. Calcination avoids thermal stress concentration caused by excessively rapid heating, ensuring the integrity of the particles. The final obtained flake-like cobalt tetroxide precursor retains the microstructure of tightly packed small pyramidal primary particles on its surface, exhibiting a unique flake-like structure.

[0033] The following section describes the preparation of different products using specific data.

[0034] The preparation method of flake-like cobalt tetroxide precursor A, the specific steps are as follows: (1) Preparation of base solution: Prepare ammonium bicarbonate solution A with a concentration of 20 g / L, adjust the temperature to 35℃, adjust the pH value to 9.0 with ammonia water, and add 200 L of this solution to a stainless steel reactor with an effective volume of 1000 L as the base solution.

[0035] (2) Preparation of cobalt salt mixed solution: Prepare a cobalt chloride solution with a cobalt content of 140 g / L at 25 °C. Add aluminum sulfate solution to the solution, controlling the mass of aluminum to be 1.0% of the mass of cobalt, and mix thoroughly to obtain a cobalt salt mixed solution.

[0036] (3) Preparation of precipitant: Prepare ammonium bicarbonate solution B with a concentration of 200 g / L at a temperature of 25℃ and a pH of 9.0.

[0037] (4) Nucleation reaction: Turn on the stirrer in the reactor, set the speed to 450 r / min, and control the temperature at 40℃. Add the cobalt salt mixed solution and ammonium bicarbonate solution B to the reactor in parallel flow, controlling the molar ratio of ammonium bicarbonate solution B to cobalt salt mixed solution to be 4.0. Adjust the flow rate to stabilize the pH of the reaction system at 8.4. After the reaction has been running for 30 hours, take a sample for testing. The D50 particle size is about 15 μm, and spherical cobalt carbonate nuclei are obtained by the accumulation of dot-like primary particles.

[0038] (5) Shell formation reaction: Continue feeding until D50 reaches 19 μm, then switch processes. Increase the reaction temperature to 55℃, reduce the stirring speed to 100 r / min, and adjust the feed flow rate to lower the pH of the system to 7.6. Continue the reaction for 20 hours, dividing the reactor twice during this period. Stop feeding when D50 reaches 21 μm. Pump the slurry into a centrifuge for centrifugal washing to obtain the cobalt carbonate precursor.

[0039] (6) Calcination: The cobalt carbonate precursor is fed into a rotary kiln at a temperature of 750°C for 3 hours to obtain a flake-like cobalt tetroxide precursor.

[0040] Testing revealed that the product prepared in this embodiment exhibited good sphericity, a distinct scaly surface structure, and a tap density of 2.3 g / cm³. 3 The particles showed no cracking, such as Figure 1 As shown.

[0041] The preparation method of flake-like cobalt tetroxide precursor B differs from that of product A in that: In step (2), the amount of aluminum salt added is 0.5% of the mass of cobalt. In step (4), the stirring speed during the nucleation reaction stage is 500 r / min, and the pH value is 8.0. In step (5), the temperature during the shell-forming reaction stage is increased to 60℃, the stirring speed is decreased to 50 r / min, and the pH value is 7.2.

[0042] Testing revealed that the product prepared in this embodiment exhibited a more pronounced scaly structure on its surface, with primary particles displaying a sharp, pyramidal shape, and a slightly increased specific surface area compared to Example 1.

[0043] The preparation method of the flake-like cobalt tetroxide precursor C differs from that of product A in that: In step (4), the stirring speed during the nucleation reaction stage is 400 r / min and the pH value is 8.8. In step (5), the temperature during the shell-forming reaction stage is increased to 45℃, the stirring speed is decreased to 200 r / min, and the pH value is 8.1.

[0044] Testing revealed that the product prepared in this embodiment has a high tap density and a dense, smooth particle surface, making it suitable for applications requiring extremely high energy density.

[0045] The preparation method of cobalt tetroxide precursor D adopts a conventional constant parameter process, and the specific steps are as follows: (1) Preparation of the base solution: Same as product A. (2) Preparation of the cobalt salt mixed solution: The amount of aluminum added is 4.0% of the mass of cobalt (outside the scope of this invention). (3) Preparation of the precipitant: Same as product A. (4) Reaction process: The reaction temperature is controlled at a constant 40℃, the stirring speed is controlled at a constant 300r / min, and the pH value is controlled at a constant 8.5. The molar ratio of ammonium bicarbonate solution B to cobalt salt mixed solution is 5.0. The reaction process is not controlled in stages, and the feed is continuously fed until D50 reaches 21μm. (5) Calcination: Same as product A.

[0046] Testing revealed that the product prepared in Comparative Example 1 had a smooth surface but no flaky structure, obvious internal cracks in the particles, and a tap density of only 2.0 g / cm³. 3 This is because the lack of phased control resulted in disordered particle arrangement at one stage, and the excessively high aluminum doping level led to severe lattice distortion. Uneven stress release during calcination caused cracking. Figure 2 As shown.

[0047] The preparation method of cobalt tetroxide precursor E differs from that of product 1 in that: During the shell-forming stage (when D50 reaches 19μm), no heating was performed, and the temperature remained at 40℃; no significant speed reduction was performed, and the stirring speed was only reduced to 250r / min.

[0048] Testing revealed that the product prepared in Comparative Example 2 had insufficient surface roughness, with primary particles exhibiting rounded and blunt shapes, failing to form a distinct pyramidal dense shell. This indicates that pH adjustment alone cannot achieve the construction of a dense shell; the synergistic effect of temperature and stirring speed is crucial.

[0049] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a flake-like cobalt tetroxide precursor, characterized in that, Includes the following steps: Step 1: Prepare ammonium bicarbonate solution A and ammonium bicarbonate solution B. Add ammonium bicarbonate solution A to the reaction vessel as the base solution. Step 2: Add aluminum salt to the cobalt salt solution to prepare a cobalt salt mixed solution. Add the cobalt salt mixed solution and ammonium bicarbonate solution B in parallel to the reactor to carry out the first stage of nucleation reaction and generate spherical cobalt carbonate nuclei. The conditions for the nucleation reaction in the first stage are as follows: the pH value of the reaction system is 8.0~8.8, the stirring speed is 300~400 r / min, the reaction time is controlled at 0~30h, the stirring speed is 400~500 r / min, and the reaction time is controlled at 30h until D50 reaches 18μm, the stirring speed is adjusted to 300~400 r / min. Step 3: Continue to introduce the cobalt salt mixed solution and ammonium bicarbonate solution B into the reactor to carry out the second stage of shell-forming reaction. During the shell-forming reaction, the reaction temperature is increased and the stirring speed is decreased, so that the primary particles grow on the surface of the spherical cobalt carbonate core to form a dense shell. After the reaction reaches the target particle size, the cobalt carbonate precursor is obtained by solid-liquid separation. The conditions for the shell-forming reaction in the second stage are as follows: the pH value of the reaction system is 7.2~8.1, the stirring speed is 50~200 r / min; when the D50 reaches 18~20 μm, the reaction temperature is raised to 45~60℃ and maintained for 10~30 h. Step 4: The second stage of the shell-forming reaction is stopped when the D50 reaches 20~22μm, and the process is carried out in separate reactors 1~4 times during the process; the cobalt carbonate precursor is calcined to obtain a flake-like cobalt tetroxide precursor.

2. The method for preparing a flake-like cobalt tetroxide precursor according to claim 1, characterized in that, The concentration of ammonium bicarbonate solution A is 15~27 g / L, the temperature is 30~40℃, and the pH value is 8~10; the concentration of ammonium bicarbonate solution B is 150~300 g / L, the temperature is 20~30℃, and the pH value is 8~10.

3. The method for preparing a flake-like cobalt tetroxide precursor according to claim 1, characterized in that, The cobalt salt solution is one or a mixture of cobalt chloride solution, cobalt sulfate solution, and cobalt nitrate solution. The cobalt content in the cobalt salt solution is 100~180g / L, the temperature is 20~30℃, and the pH value is 1~3.

4. The method for preparing a flake-like cobalt tetroxide precursor according to claim 1, characterized in that, The aluminum salt is one or a mixture of aluminum sulfate, aluminum chloride, and aluminum nitrate, and the amount of aluminum salt added is 0.5-3% of the cobalt content in the cobalt salt solution.

5. The method for preparing a flake-like cobalt tetroxide precursor according to claim 1, characterized in that, In both the first and second stages of the reaction, the molar ratio of ammonium bicarbonate solution B to the cobalt salt mixture is 3.5 to 4.

5.

6. The method for preparing a flake-like cobalt tetroxide precursor according to claim 1, characterized in that, The temperature of the first stage nucleation reaction is 35~45℃, the dense shell is formed by the close arrangement of small pyramidal primary particles, and the aluminum element in the aluminum salt is uniformly embedded in the shell.

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