Process for the preparation of cobalt carbonate and tricobalt tetraoxide

Abstract

The application discloses a preparation method of cobalt carbonate, which comprises the following steps: configuring a solution; under stirring, synthesizing cobalt carbonate seeds by reacting an aluminum-doped cobalt salt solution and a carbonate solution; and under stirring, continuously feeding the aluminum-doped cobalt salt solution and the carbonate solution into a growth kettle containing the cobalt carbonate seeds, so that the cobalt carbonate seeds are synthesized and grown into cobalt carbonate particles and reach a target particle size; wherein, at a predetermined time before the end of feeding, the pH value of the solution in the growth kettle is reduced by more than 0.3 from an initial pH value to reach a low pH value and is kept; then the pH value is increased by more than 0.3 from the low pH value, and is kept at the high pH value until the end of feeding. The application also discloses a preparation method of cobalt carbonate. According to the application, the aluminum-doping uniformity of the cobalt carbonate in the wet synthesis process is improved, and finally the aluminum-doping uniformity of the cobalt carbonate is improved.

Description

Technical Field

[0001] This invention belongs to the field of materials preparation technology, and specifically relates to a method for preparing cobalt carbonate and cobalt tetroxide to improve the uniformity of aluminum doping. Background Technology

[0002] With the continuous upgrading of 3C products, especially 5G mobile phones, the requirements for the battery life and size of lithium-ion batteries are constantly increasing, making it urgent to further improve the volumetric energy density of batteries. Aluminum-doped cobalt tetroxide (LCO) is an important precursor for preparing lithium cobalt oxide (LiCoO2), a high-voltage lithium battery cathode material, and its various properties affect the performance of both the LiCoO2 cathode material and downstream lithium-ion batteries. Aluminum doping can effectively improve the stability of the LCO crystal structure, preventing crystal structure collapse during charge and discharge, allowing more lithium ions to participate in charge and discharge, thereby improving the cycle performance of LCO at high voltage and effectively increasing the specific capacity of LiCoO2. However, currently, the aluminum-doped cobalt tetroxide prepared in the industry generally suffers from uneven aluminum distribution, which seriously affects the electrical performance of downstream cathode materials and the quality of the final product.

[0003] Cobalt carbonate is a crucial raw material in the lithium cobalt oxide cathode material industry. Cobalt carbonate is calcined to form cobalt tetroxide, which can then be further reacted with lithium carbonate to produce lithium cobalt oxide. The uniformity of aluminum doping in cobalt carbonate particles directly affects the uniformity of aluminum doping in the calcined cobalt tetroxide, thus influencing the electrochemical performance of high-voltage LCOs.

[0004] There is an urgent need to improve the uniformity of aluminum doping in cobalt carbonate and cobalt tetroxide. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing cobalt carbonate and cobalt tetroxide with improved aluminum doping uniformity, which improves the aluminum doping uniformity of cobalt carbonate / cobalt tetroxide.

[0006] According to one aspect of the present invention, a method for preparing cobalt carbonate is provided, the method comprising the following steps:

[0007] (1) Prepare aluminum-doped cobalt salt solution and carbonate solution;

[0008] (2) Under stirring conditions, the aluminum-doped cobalt salt solution and the carbonate solution are reacted to synthesize cobalt carbonate seed crystals;

[0009] (3) Under stirring conditions, the aluminum-doped cobalt salt solution and the carbonate solution are continuously added to the growth vessel containing the cobalt carbonate seed crystals, so that the cobalt carbonate seed crystals are synthesized and grown into cobalt carbonate particles and reach the target particle size. In the predetermined time before the end of feeding, the pH value of the solution in the growth vessel is reduced from the initial pH value to a first predetermined value or higher, reaching a low pH value and maintaining it; then the pH value is increased from the low pH value to a second predetermined value or higher, and maintained at the high pH value until the end of feeding.

[0010] Optionally, the first predetermined value and the second predetermined value are both 0.3.

[0011] Optionally, in step (3), the time from the start of lowering the pH value to the start of raising the pH value is 2 to 10 hours; the time from the start of raising the pH value to the end of feeding is 5 to 40 hours.

[0012] Optionally, in step (3), the pH value of the lower position is 5.8 to 7.5; and the pH value of the higher position is 7.2 to 8.2.

[0013] Optionally, in step (3), the pH value of the lower position is 6.0 to 7.2; and the pH value of the higher position is 7.5 to 8.0.

[0014] Optionally, in step (3), the initial pH value is 7.2 to 8.5.

[0015] Optionally, in step (3), the initial pH value is 7.5 to 8.0.

[0016] Optionally, the total growth time of cobalt carbonate particles in step (3) is 50 to 180 hours; the target particle size is 3 to 25 μm.

[0017] Optionally, the total time for the synthesis and growth of cobalt carbonate particles in step (3) is 80 to 150 hours.

[0018] Optionally, in step (3), the feed flow rate of the aluminum-doped cobalt salt solution is reduced by 40% to 90% 15 to 50 hours before the end of the feeding process.

[0019] Optionally, in step (3), after the pH value is lowered, the operation of reducing the feed flow rate of the aluminum-cobalt salt solution by 40-90% is carried out.

[0020] Optionally, the aluminum-doped cobalt salt solution includes one or more cobalt salts selected from cobalt sulfate, cobalt chloride, and cobalt nitrate, wherein the cobalt ion concentration in the aluminum-doped cobalt salt solution is 80–145 g / L, and the aluminum-cobalt mass ratio is 0.0027–0.028; and the carbonate solution includes one or more selected from ammonium bicarbonate solution, ammonium carbonate solution, sodium bicarbonate solution, and sodium carbonate solution, wherein the carbonate solution concentration is 200–240 g / L.

[0021] Optionally, in step (3), the feed flow rates of the aluminum-doped cobalt salt solution and the carbonate solution are controlled so that the mass ratio of cobalt to carbonate is 0.16 to 0.30.

[0022] Optionally, in step (2), the diluted solution of the carbonate solution is used as the base liquid, and the aluminum-doped cobalt salt solution and the carbonate solution are added to the reaction vessel under stirring conditions to react and synthesize cobalt carbonate seed crystals, and then the cobalt carbonate seed crystals are transferred to the growth vessel.

[0023] According to another aspect of the present invention, a method for preparing cobalt tetroxide with improved aluminum doping uniformity is provided, comprising: preparing cobalt carbonate particles according to the cobalt carbonate preparation method described above; and calcining the cobalt carbonate particles to obtain cobalt tetroxide.

[0024] According to another aspect of the present invention, cobalt carbonate particles are provided, which are prepared by the cobalt carbonate preparation method described above.

[0025] According to another aspect of the present invention, a cobalt tetroxide material is provided, which is prepared by the cobalt tetroxide preparation method described above.

[0026] According to an embodiment of the present invention, the reaction solution system environment is altered. First, the pH value is lowered, at which point aluminum is amorphously dispersed within the cobalt carbonate bulk phase. Then, the pH value is raised, inducing a transformation in the precipitated components and morphology of aluminum, i.e., a transformation from unstable aluminum carbonate to stable cobalt aluminum hydrotalcite. During this stage, a large number of cobalt aluminum hydrotalcite nuclei are generated, uniformly distributed on the surface of the cobalt carbonate particles, forming tiny pores. Subsequently, the reaction system is maintained at a high pH value to continue the reaction. Due to the large proportion of the cobalt carbonate phase and the small proportion and large number of cobalt aluminum hydrotalcite nuclei, the cobalt carbonate particles accumulate at a much faster rate than cobalt aluminum hydrotalcite. Therefore, the tiny pores on the surface of the spherical particles are gradually filled by the cobalt carbonate particles, forming smooth cobalt carbonate spheres embedded with crystalline aluminum compounds. This achieves uniform aluminum doping in the carbonate system to a certain extent, while the cobalt aluminum hydrotalcite exhibits good stability, thus preventing segregation and enrichment during washing and storage. This is beneficial for industrial production and improves the electrical performance of high-voltage LCOs. Attached Figure Description

[0027] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0028] Figure 1 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Example 1 of this invention;

[0029] Figure 2 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Comparative Example 1 of this invention;

[0030] Figure 3 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Example 2A of the present invention;

[0031] Figure 4 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Example 2B of the present invention;

[0032] Figure 5 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Example 2C of this invention;

[0033] Figure 6 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Comparative Example 2 of this invention;

[0034] Figure 7 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Example 3 of the present invention;

[0035] Figure 8 This is a SEM image (3000x magnification) of aluminum-doped cobalt carbonate obtained in Comparative Example 3 of this invention;

[0036] Figure 9 This is a SEM image (10000x magnification) of aluminum-doped cobalt tetroxide obtained in Example 4 of the present invention;

[0037] Figure 10 This is a SEM image (10000x magnification) of aluminum-doped cobalt tetroxide obtained in Comparative Example 4 of this invention;

[0038] Figure 11 This is a SEM image (10000x magnification) of aluminum-doped cobalt tetroxide obtained in Example 5 of the present invention;

[0039] Figure 12 This is a SEM image (10000x magnification) of aluminum-doped cobalt tetroxide obtained in Comparative Example 5 of this invention. Detailed Implementation

[0040] The present application will now be described in further detail with reference to the accompanying drawings and embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit the invention.

[0041] The inventors of this invention discovered that during the synthesis and growth stage of wet synthesis of cobalt carbonate particles, by changing the pH value of the reaction solution system in a specific manner—specifically, by lowering the pH value used in normal synthesis and growth (referred to as the "initial pH value" in this application, meaning "the pH value before the change") and then raising it again after a period of time—aluminum can first be dispersed in an amorphous state into the cobalt carbonate bulk phase, and then the unstable aluminum carbonate can be induced to transform into stable cobalt aluminum hydrotalcite, generating a large number of cobalt aluminum hydrotalcite nuclei, which are then uniformly distributed on the surface of the cobalt carbonate particles and form fine pores. Subsequently, by maintaining the reaction system at a high pH value and continuing the reaction, the cobalt carbonate particles with a relatively faster stacking rate can be used to fill the fine pores on the surface of the cobalt carbonate spherical particles, thereby embedding crystalline aluminum compounds into the surface of the cobalt carbonate particles and forming smooth cobalt carbonate spheres.

[0042] Based on the above findings, the proposed method for preparing cobalt carbonate of the present invention includes the following steps:

[0043] (1) Solution preparation: Prepare aluminum-doped cobalt salt solution and carbonate solution;

[0044] (2) Seed preparation: Under stirring conditions, aluminum-doped cobalt salt solution and carbonate solution are reacted to synthesize cobalt carbonate seed crystals;

[0045] (3) Synthesis and growth: Under stirring conditions, aluminum-doped cobalt salt solution and carbonate solution are continuously added to the growth vessel containing the cobalt carbonate seed crystals to synthesize and grow the cobalt carbonate seed crystals into cobalt carbonate particles and achieve the target particle size. At a predetermined time before the end of feeding, the pH value of the solution in the growth vessel is reduced from the initial pH value to a first predetermined value or higher, reaching a low pH value and maintaining it; then the pH value is increased from the low pH value to a second predetermined value or higher, and maintained at the high pH value until the end of feeding.

[0046] In step (1), the aluminum-doped cobalt salt solution may include one or more cobalt salts selected from, for example, cobalt sulfate, cobalt chloride, and cobalt nitrate. The carbonate solution may include one or more selected from ammonium bicarbonate solution, ammonium carbonate solution, sodium bicarbonate solution, and sodium carbonate solution. The concentrations of the aluminum-doped cobalt salt and the carbonate solution can be reasonably determined empirically based on conditions such as desired production efficiency and aluminum doping amount. For example, the cobalt ion concentration in the aluminum-doped cobalt salt solution may be 80–145 g / L, the aluminum-cobalt mass ratio may be 0.0027–0.028, and the carbonate solution concentration may be 200–240 g / L.

[0047] In step (2), a diluted solution of carbonate solution can be added to the reactor as a base solution, and the aluminum-doped cobalt salt solution and carbonate solution can be added to the reactor under stirring conditions to synthesize cobalt carbonate seed crystals. If necessary, the obtained cobalt carbonate seed crystals can be transferred to a growth reactor for subsequent synthesis and growth reactions; however, those skilled in the art will understand that this is not necessary.

[0048] In step (3), the first predetermined value associated with a decrease in pH and the second predetermined value associated with an increase in pH can be selected as 0.3. It should be understood that the first predetermined value and the second predetermined value can be the same as or different from each other.

[0049] In step (3), the feed flow rates of the aluminum-doped cobalt salt solution and the carbonate solution can be controlled to ensure that the mass ratio of cobalt to carbonate is 0.16 to 0.30.

[0050] In step (3), the time from the start of lowering the pH value to the start of raising the pH value can be 2 to 10 hours. If this time is too short, there may not be enough time for the amorphous aluminum compound to be fully formed and dispersed in the cobalt carbonate bulk phase; if it is too long, an excessive amount of amorphous aluminum compound may be formed, which is not conducive to the subsequent fixation of the aluminum sheet by cobalt carbonate microcrystals.

[0051] Furthermore, the time from the start of pH increase to the end of feeding can be 5 to 40 hours. If this time is too short, the generated crystalline aluminum compound cannot be sufficiently fixed; if it is too long, localized honeycomb-like aluminum enrichment may still recur on the surface of the continuing-growing cobalt carbonate particles.

[0052] In this application, the initial pH value refers to the pH value used in the wet synthesis of cobalt carbonate particles without incorporating the pH value alteration treatment of this invention. The initial pH value may vary depending on conditions and expectations, such as the concentration of the solution used, the feed flow rate, and the target particle size. For example, it may be 7.2 to 8.5, or optionally 7.5 to 8.0.

[0053] In step (3), the lower pH value can be 5.8 to 7.5, or 6.0 to 7.2; the higher pH value can be 7.2 to 8.2, or 7.5 to 8.0.

[0054] The cobalt carbonate preparation method of the present invention can be used to prepare cobalt carbonate particles with a particle size of 3 to 25 μm. Correspondingly, the synthesis and growth time in the preparation process can vary within a wide range, for example, it can be 50 to 180 hours, and optionally 80 to 150 hours.

[0055] Optionally, in step (3), the feed flow rate of the aluminum cobalt salt solution can be reduced by 40-90% 15-50 hours before the end of the feeding process. For example, the operation of reducing the feed flow rate of the aluminum cobalt salt solution by 40-90% can be carried out after the pH value is lowered.

[0056] The embodiments and comparative examples of the present invention are described below. It should be understood that the present invention is not limited to these embodiments in any way.

[0057] <Example 1>

[0058] Solution preparation: Prepare an aluminum-doped cobalt sulfate solution with a cobalt ion concentration of 100 g / L and an aluminum-cobalt mass ratio of 0.0125; prepare an ammonium bicarbonate solution with an ammonium bicarbonate concentration of 200 g / L.

[0059] Seed preparation: Ammonium bicarbonate solution and water were injected into the reactor as the base liquid. While the reactor was being stirred, the prepared cobalt aluminum sulfate solution and ammonium bicarbonate solution were pumped into the reactor in proportion, wherein the mass ratio of cobalt metal to ammonium bicarbonate was 0.3, the temperature was 50℃, the stirring speed was 180 rpm, and after 40 hours, 9.0 μm seed crystals were obtained and transferred to the growth reactor.

[0060] Synthetic growth: Under stirring at 100 rpm, aluminum-doped cobalt sulfate solution and ammonium bicarbonate solution were pumped into the growth vessel in a specific ratio, with the mass ratio of cobalt metal to ammonium bicarbonate being 0.3. The flow rate of the aluminum-doped cobalt sulfate solution was 50 ml / min. Once the material in the growth vessel reached its upper limit, feeding and stirring were stopped. After settling, the supernatant was removed, and stirring and feeding were resumed. This process was repeated multiple times until the target particle size D50 of 20–21 μm was achieved. Feeding was then stopped, yielding an aluminum-doped cobalt carbonate slurry, which was then temporarily stored in an aging tank.

[0061] The above-mentioned synthesis and growth process is divided into an initial stage, a pH decrease stage, and a pH increase stage. In the initial stage, the pH value of the solution in the growth vessel is controlled at 7.5, and the duration of the initial stage is T0, which is 138 hours. Then, the pH decrease stage is entered, in which the pH value is decreased from 7.5 to 7.2, and the duration of the pH decrease stage is T1, which is 2 hours. Finally, the pH increase stage is entered, in which the pH value is increased from 7.2 to 7.5 by adding cobalt aluminum sulfate solution and ammonium bicarbonate solution and the pH value is maintained until the end of the feeding, and the duration of the pH increase stage is T2, which is 10 hours.

[0062] Washing and Drying: The aluminum-doped cobalt carbonate slurry in the aging tank was pumped into a centrifuge and rinsed with pure water. After centrifugation and dehydration, wet aluminum-doped cobalt carbonate was obtained. The wet aluminum-doped cobalt carbonate was then dried. The SEM image of the obtained aluminum-doped cobalt carbonate is shown below. Figure 1 .

[0063] Calcination: The dried aluminum-doped cobalt carbonate is calcined in a rotary kiln in two stages. The first stage calcination temperature is 500℃ and the calcination time is 3 hours; the second stage calcination temperature is 850℃ and the calcination time is 5 hours. After calcination, the mixture is stirred for 5 minutes to obtain aluminum-doped cobalt tetroxide.

[0064] <Comparative Example 1>

[0065] In Comparative Example 1, the synthesis and growth process was maintained at pH 7.5, without any pH decreasing or increasing stages, and otherwise proceeded in the same manner as in Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 2 .

[0066] <Example 2A>

[0067] In Example 2A, the pH of the solution in the growth vessel was controlled at 7.7 in the initial stage for 100 hours (T0); in the pH-decreasing stage, the pH was decreased from 7.7 to 7.0 for 10 hours (T1); and in the pH-increasing stage, the pH was increased from 7.0 to 7.7 and maintained until the feeding was completed for 40 hours (T2). Otherwise, Example 2A was performed identically to Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 3 .

[0068] <Example 2B>

[0069] In Example 2B, the pH of the solution in the growth vessel was controlled at 7.7 in the initial stage for 100 hours (T0); in the pH-decreasing stage, the pH was decreased from 7.7 to 7.0 for 10 hours (T1); and in the pH-increasing stage, the pH was increased from 7.0 to 7.7 and maintained until the end of the feeding process for 40 hours (T2). Simultaneously with the pH increase, the feed flow rate of the aluminum-doped cobalt sulfate solution was reduced by 60%, i.e., to 20 ml / min. Otherwise, Example 2B was performed identically to Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 4 .

[0070] <Example 2C>

[0071] In Example 2C, the pH of the solution in the growth vessel was controlled at 7.7 in the initial stage for 138 hours (T0); in the pH-decreasing stage, the pH was lowered from 7.7 to 6.0 for 2 hours (T1); and in the pH-raising stage, the pH was raised from 6.0 to 8.0 and maintained until the end of the feeding process for 10 hours (T2). Otherwise, Example 2C was performed in the same manner as Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 5 .

[0072] <Comparative Example 2>

[0073] In Comparative Example 2, the pH value was maintained at 7.7 during the synthesis and growth process, without any pH decrease or increase phases. Otherwise, the process was the same as in Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 6 .

[0074] <Example 3>

[0075] In Example 3, the pH of the solution in the growth vessel was controlled at 8.0 in the initial stage for 115 hours (T0); the pH was lowered from 8.0 to 7.0 in the initial stage for 10 hours (T1); and the pH was raised from 7.0 to 8.0 in the subsequent stage until the feeding was completed for 25 hours (T2). Otherwise, Example 3 was performed in the same manner as Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 7 .

[0076] <Comparative Example 3>

[0077] In Comparative Example 3, the pH value was maintained at 8.0 during the synthesis and growth process, without any pH decrease or increase phases. Otherwise, the process was the same as in Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt carbonate is shown below. Figure 8 .

[0078] <Example 4>

[0079] Solution preparation: Prepare an aluminum-doped cobalt sulfate solution with a cobalt ion concentration of 145 g / L and an aluminum-cobalt mass ratio of 0.0139; prepare an ammonium bicarbonate solution with an ammonium bicarbonate concentration of 220 g / L.

[0080] Seed preparation: Ammonium bicarbonate solution and water were injected into the reactor as the base liquid. While the reactor was being stirred, the prepared aluminum-doped cobalt sulfate solution and ammonium bicarbonate solution were pumped into the reactor in proportion. The mass ratio of cobalt metal to ammonium bicarbonate was 1:1. The temperature was 1:1. The stirring speed was 200 rpm. After 10 hours, 1.8 μm seed crystals were obtained and transferred to the growth reactor.

[0081] Synthetic growth: Under stirring at 200 rpm, aluminum-doped cobalt sulfate solution and ammonium bicarbonate solution were pumped into the growth vessel in a specific ratio, with the mass ratio of cobalt metal to ammonium bicarbonate being 0.16. The feed flow rate of the aluminum-doped cobalt sulfate solution was 40 ml / min. Once the material in the growth vessel reached its upper limit, feeding and stirring were stopped. After the material settled, the supernatant was removed, and stirring and feeding were resumed. This process was repeated multiple times until the target particle size D50 of 3.0–4.0 μm was achieved. Feeding was then stopped, yielding an aluminum-doped cobalt carbonate slurry, which was then temporarily stored in an aging tank.

[0082] The above-mentioned synthesis and growth process is divided into an initial stage, a pH decreasing stage, and a pH increasing stage. In the initial stage, the pH of the solution in the growth vessel is controlled at 7.5, and the duration of the initial stage is T0, which is 55 hours. Then, the pH decreasing stage is entered, in which the pH is decreased from 7.5 to 7.2, and the duration of the pH decreasing stage is T1, which is 10 hours. Finally, the pH increasing stage is entered, in which the pH is increased from 7.2 to 7.5 by adding cobalt aluminum sulfate solution and ammonium bicarbonate solution and the pH is maintained until the feeding is completed, and the duration of the pH increasing stage is T2, which is 25 hours.

[0083] Washing and drying: The aluminum-doped cobalt carbonate slurry in the aging tank is pumped into a centrifuge and rinsed with pure water. After centrifugation and dehydration, the aluminum-doped cobalt carbonate wet material is obtained. The aluminum-doped cobalt carbonate wet material is then dried to obtain aluminum-doped cobalt carbonate.

[0084] Calcination: The dried aluminum-doped cobalt carbonate was calcined in a rotary kiln in two stages. The first stage calcination temperature was 400℃, and the calcination time was 3 hours; the second stage calcination temperature was 750℃, and the calcination time was 5 hours. After calcination, the mixture was stirred for 15 minutes to obtain aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt tetroxide is shown below. Figure 9 .

[0085] <Comparative Example 4>

[0086] In Comparative Example 4, the pH value was maintained at 7.5 during the synthesis and growth process, without any pH decrease or increase phases. Otherwise, the process was the same as in Example 4, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt tetroxide is shown below. Figure 10 .

[0087] <Example 5>

[0088] In Example 5, the pH of the solution in the growth vessel was controlled at 8.0 in the initial stage for 70 hours (T0); in the pH-decreasing stage, the pH was decreased from 8.0 to 7.2 for 5 hours (T1); and in the pH-increasing stage, the pH was increased from 7.2 to 7.8 and maintained until the feeding was completed for 5 hours (T2). Otherwise, Example 5 was performed in the same manner as Example 1, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt tetroxide is shown below. Figure 11 .

[0089] <Comparative Example 5>

[0090] In Comparative Example 5, the pH value was maintained at 8.0 during the synthesis and growth process, without any pH decrease or increase phases. Otherwise, the process was the same as in Example 4, yielding aluminum-doped cobalt carbonate and aluminum-doped cobalt tetroxide. The SEM image of the aluminum-doped cobalt tetroxide is shown below. Figure 12 .

[0091] The preparation conditions of the above embodiments and comparative examples are shown in Table 1, and the relevant parameters of the aluminum-doped cobalt tetroxide obtained in each embodiment and comparative example are shown in Table 2.

[0092] [Table 1]

[0093]

[0094] [Table 2]

[0095]

[0096] Figure 1 , Figure 3 , Figure 4 , Figure 5 and Figure 7 The image shown is a SEM image of the cobalt carbonate particles obtained in Examples 1, 2A-2C, and 3. Figure 2 , Figure 6 and Figure 8 The image shown is a SEM image of the cobalt carbonate particles obtained in Comparative Examples 1–3. Figure 2 , Figure 6 and Figure 8 As can be seen, the cobalt carbonate particles in Comparative Examples 1-3 all exhibit localized honeycomb-like aluminum enrichment, as shown by the dark spots on the particle surface in the figure. In contrast, as... Figure 1 , Figure 3 , Figure 4 , Figure 5 and Figure 7 As shown in the corresponding embodiment, the large dark spots (caused by aluminum enrichment) on the particle surface have essentially disappeared, indicating that the honeycomb aluminum enrichment has been eliminated or alleviated. Instead, aluminum compounds are more uniformly embedded on the surface of the cobalt carbonate particles, indicating that the uniformity of aluminum distribution in the cobalt carbonate particles has been improved.

[0097] Furthermore, in comparison Figure 3 SEM images of cobalt carbonate particles obtained in Example 2A and Figure 4 The SEM image of the cobalt carbonate particles obtained in Example 2B shows that the surface of the cobalt carbonate particles obtained in Example 2B is significantly more uniform and smooth. The areas with and without aluminum compounds are virtually indistinguishable to the naked eye in the image. Accordingly, this indicates that in Example 2B, compared to Example 2A, reducing the feed flow rate of the aluminum-doped cobalt salt solution while initially increasing the pH value further improved the aluminum doping uniformity of the obtained cobalt carbonate particles.

[0098] Figure 9 and Figure 11 The image shown is an SEM image of the cobalt tetroxide particles obtained in Examples 4 and 5. Figure 10 and Figure 12 The image shown is a SEM image of the cobalt tetroxide particles obtained in Comparative Examples 4 and 5. From... Figure 10 and Figure 12 As can be seen, on the surface of the cobalt tetroxide particles in Comparative Examples 4 and 5, aluminum flakes clearly protrude (see the sheet-like structure shown in the figure) and aggregate to form localized honeycomb-like aluminum enrichment. In contrast, as... Figure 9 and Figure 11 As shown in Examples 4 and 5, there are basically no obvious protruding aluminum flakes on the surface of the cobalt tetroxide particles. The aluminum flakes are embedded relatively evenly in the particle surface, and no obvious honeycomb-like aluminum enrichment is formed.

[0099] Furthermore, as can be seen from the relevant parameters of aluminum-doped cobalt tetroxide obtained in the various embodiments and comparative examples shown in Table 2, the preparation methods of cobalt carbonate and cobalt tetroxide according to the embodiments of the present invention are beneficial to obtaining better tap density characteristics of cobalt tetroxide particles.

[0100] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the inventive concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. A method for preparing cobalt carbonate, comprising the following steps: (1) Prepare aluminum-doped cobalt salt solution and carbonate solution; (2) Under stirring conditions, the aluminum-doped cobalt salt solution and the carbonate solution are reacted to synthesize cobalt carbonate seed crystals; (3) Under stirring conditions, the aluminum-doped cobalt salt solution and the carbonate solution are continuously added to the growth vessel containing the cobalt carbonate seed crystals, so that the cobalt carbonate seed crystals are synthesized and grown into cobalt carbonate particles and reach the target particle size. The step (3) is divided into an initial stage, a pH decrease stage, and a pH increase stage. In the initial stage, the pH value of the solution in the growth vessel is maintained at the initial pH value; The pH reduction stage is entered at a predetermined time before the feeding ends, wherein the pH value of the solution in the growth vessel is reduced from the initial pH value to a first predetermined value or higher, reaching a low pH value and maintaining it, so as to generate unstable aluminum carbonate, wherein the low pH value is 5.8 to 7.

5. During the pH-raising stage, the pH value is raised from the low pH value to a higher pH value of greater than 7.5 and less than or equal to 8.2, thereby inducing the unstable aluminum carbonate to transform into stable cobalt aluminum hydrotalcite, generating cobalt aluminum hydrotalcite crystal nuclei, and then maintaining the high pH value until the feeding is completed.

2. The method for preparing cobalt carbonate as described in claim 1, wherein, The first predetermined value is 0.3, and the second predetermined value is 0.

3.

3. The method for preparing cobalt carbonate as described in claim 1, wherein, In step (3), the time from the start of lowering the pH value to the start of raising the pH value is 2 to 10 hours; the time from the start of raising the pH value to the end of feeding is 5 to 40 hours.

4. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, The lower pH value is 6.0~7.2, and the higher pH value is greater than 7.5 and less than or equal to 8.

0.

5. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, In step (3), the initial pH value is 7.2~8.

5.

6. The method for preparing cobalt carbonate as described in claim 5, wherein, The initial pH value is 7.5~8.

0.

7. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, The total growth time for the cobalt carbonate particles in step (3) is 50 to 180 hours; the target particle size is 3 to 25 μm.

8. The method for preparing cobalt carbonate as described in claim 7, wherein, The total time for the synthesis and growth of cobalt carbonate particles in step (3) is 80 to 150 hours.

9. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, In step (3), 15 to 50 hours before the end of feeding, the feeding flow rate of the aluminum-cobalt salt solution is reduced by 40 to 90%.

10. The method for preparing cobalt carbonate as described in claim 9, wherein, In step (3), after the pH value is lowered, the operation of reducing the feed flow rate of the aluminum-doped cobalt salt solution by 40-90% is carried out.

11. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, The aluminum-doped cobalt salt solution comprises one or more cobalt salts selected from cobalt sulfate, cobalt chloride, and cobalt nitrate, wherein the cobalt ion concentration in the aluminum-doped cobalt salt solution is 80~145 g / L, and the aluminum-to-cobalt mass ratio is 0.0027~0.028; and The carbonate solution includes one or more selected from ammonium bicarbonate solution, ammonium carbonate solution, sodium bicarbonate solution, and sodium carbonate solution, and the concentration of the carbonate solution is 200~240 g / L.

12. The method for preparing cobalt carbonate as described in claim 11, wherein, In step (3), the feed flow rates of the aluminum-doped cobalt salt solution and the carbonate solution are controlled so that the mass ratio of cobalt to carbonate is 0.16 to 0.

30.

13. The method for preparing cobalt carbonate according to any one of claims 1-3, wherein, In step (2), the diluted solution of the carbonate solution is used as the base liquid. The aluminum-doped cobalt salt solution and the carbonate solution are added to the reaction vessel under stirring conditions to synthesize cobalt carbonate seed crystals. Then, the cobalt carbonate seed crystals are transferred to the growth vessel.

14. A method for preparing cobalt tetroxide, comprising: Cobalt carbonate particles are prepared according to the cobalt carbonate preparation method according to any one of claims 1-13; And the cobalt carbonate particles are calcined to obtain cobalt tetroxide.

15. A cobalt carbonate particle prepared by any one of claims 1-13.

16. A cobalt tetroxide particle, which is prepared by the method of claim 14.

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