Preparation method for large-particle cobaltosic oxide

Abstract

The present disclosure relates to the technical field of battery material preparation, and in particular to a preparation method for a large-particle cobaltosic oxide, comprising the following steps: mixing a cobalt salt solution with a carbonate-containing precipitant solution A, performing solid-liquid separation after reaction, taking solid phase substances, and drying and crushing to obtain amorphous nano cobalt carbonate; mixing a cobalt salt solution with a carbonate-containing precipitant solution B and a carbonate-containing precipitant solution C, generating cobalt carbonate particles after reaction, then adding the amorphous nano cobalt carbonate for reaction to obtain a reaction solution containing a cobalt carbonate matrix coated with the amorphous nano cobalt carbonate; and adding a hydroxyl-containing precipitant solution D into the reaction solution, adding the cobalt salt solution and the precipitant solution D, generating mixed particles after reaction, then performing solid-liquid separation, taking solid phase substances to obtain a cobalt carbonate / cobalt hydroxide mixture, performing primary sintering and then mixing with the amorphous nano cobalt carbonate, and performing secondary sintering to obtain a large-particle cobaltosic oxide.

Description

A method for preparing large-particle cobalt tetroxide Technical Field

[0001] The present invention relates to the technical field of battery material preparation, and in particular to a method for preparing large-particle cobalt tetroxide. Background Art

[0002] Lithium cobalt oxide positive electrode materials have the advantage of high energy density and are mainly used in the 3C field. Cobalt trioxide, as a precursor of lithium cobalt oxide positive electrode materials, has been widely studied because of its stable structure, high theoretical capacity, and good electrochemical performance.

[0003] Currently available methods for preparing large-particle cobalt oxide precursors generally involve wet-process synthesis of large-particle cobalt hydroxide or cobalt carbonate, followed by high-temperature calcination. However, in actual preparation, due to the loose structure of cobalt hydroxide, the resulting large-particle cobalt oxide typically has a low tap density. While cobalt carbonate has a compact structure, it releases carbon dioxide during high-temperature calcination, which can easily cause the particles to crack and break, affecting the performance of the resulting cobalt oxide.

[0004] Therefore, there is an urgent need to develop a new method for preparing large-particle cobalt tetroxide.

[0005] Summary of the Invention

[0006] The present disclosure aims to solve at least one of the technical problems existing in the related art. To this end, the present disclosure provides a method for preparing large-particle cobalt tetroxide, which can avoid particle breakage during the preparation process and obtain large-particle cobalt tetroxide with high tap density.

[0007] The above technical objectives of the present disclosure are achieved through the following technical solutions:

[0008] A method for preparing large-particle cobalt trioxide comprises the following steps:

[0009] (1) mixing a cobalt salt solution with a precipitant solution A containing carbonate, separating the solid and the liquid after the reaction, drying and crushing the solid phase to obtain amorphous nano-cobalt carbonate;

[0010] (2) mixing the cobalt salt solution with a precipitant solution B containing carbonate and a precipitant solution C containing carbonate to react and generate cobalt carbonate particles, and then adding the amorphous nano-cobalt carbonate prepared in step (1) to react and obtain a reaction solution containing a cobalt carbonate matrix coated with the amorphous nano-cobalt carbonate;

[0011] (3) Under an inert atmosphere, adding a precipitant solution D containing hydroxide to the reaction solution of step (2) to adjust the pH to neutral or alkaline, then adding a cobalt salt solution and a precipitant solution D containing hydroxide, reacting to form mixed particles, separating the solid and the liquid, taking the solid phase to obtain a cobalt carbonate / cobalt hydroxide mixture, and sintering once to obtain a large-particle cobalt oxide semi-finished product;

[0012] (4) mixing the large-particle cobalt oxide semi-finished product obtained in step (3) with the amorphous nano-cobalt carbonate obtained in step (1), and performing secondary sintering to obtain large-particle cobalt oxide.

[0013] In one embodiment, the cobalt salt solution is at least one of cobalt chloride, cobalt nitrate, and cobalt sulfate.

[0014] In one embodiment, the concentration of cobalt ions in the cobalt salt solution is 1.5-2.0 mol / L.

[0015] In one embodiment, the precipitant solution A is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution, and a potassium carbonate solution, and the concentration of the precipitant solution A is 250-300 g / L.

[0016] In one embodiment, the precipitant solution B is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution, and a potassium carbonate solution, and the concentration of the precipitant solution B is 60-120 g / L.

[0017] In one embodiment, the precipitant solution C is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution, and a potassium carbonate solution, and the concentration of the precipitant solution C is 160-240 g.

[0018] In one embodiment, the precipitant solution D is at least one of a sodium hydroxide solution and a potassium hydroxide solution, and the concentration of the precipitant solution D is 320-480 g / L.

[0019] In one embodiment, in step (1), the cobalt salt solution is mixed with the carbonate-containing precipitant solution A with the precipitant solution A as the base solution, and then the cobalt salt solution is added.

[0020] In one embodiment, in step (1), the cobalt salt solution is added gradually under stirring.

[0021] In one embodiment, in step (1), the stirring speed is 40-50 Hz.

[0022] In one embodiment, in step (1), the reaction temperature is 25-30°C.

[0023] In one embodiment, in step (1), the pH of the reaction is 8.0-8.5.

[0024] In one embodiment, in step (1), the drying and crushing is performed using a disc-nest mill.

[0025] In one embodiment, in step (1), the D50 of the amorphous nano-cobalt carbonate is less than 1 μm.

[0026] In one embodiment, in step (2), the cobalt salt solution is mixed with the precipitant solution B containing carbonate and the precipitant solution C containing carbonate, with the precipitant solution B as the base solution, and then the cobalt salt solution and the precipitant solution C containing carbonate are added.

[0027] In one embodiment, in step (2), the adding of the cobalt salt solution and the precipitant solution C containing carbonate ions refers to first adding the cobalt salt solution and the precipitant solution C in parallel at 38-45° C., then maintaining the flow rate of the cobalt salt solution constant, adjusting the flow rate of the precipitant solution C to control the synthesized pH to 7-8, and controlling the stirring frequency to 15-20 Hz to generate cobalt carbonate particles with a D50 of 15-16 μm.

[0028] In one embodiment, in step (2), the mass of the amorphous nano-cobalt carbonate added is 1 / 20-1 / 50 of the total mass of the cobalt carbonate particles and the amorphous nano-cobalt carbonate.

[0029] In one embodiment, in step (3), after adding the precipitant solution B containing hydroxide to the reaction solution of step (2), the reaction temperature is controlled to be 60-70° C. and the stirring frequency is 10-15 Hz.

[0030] In one embodiment, in step (3), the pH is adjusted to 9-10.

[0031] In one embodiment, in step (3), adding the cobalt salt solution and the precipitant solution D means first adding the cobalt salt solution and the precipitant solution D in parallel, then maintaining the flow rate of the cobalt salt solution constant, and adjusting the flow rate of the precipitant solution D to control the synthesized pH to 9-10 until mixed particles with a D50 of 18-20 μm are generated.

[0032] In one embodiment, in step (3), the primary sintering temperature is 350-450° C., and the primary sintering time is 2-4 hours.

[0033] In one embodiment, in step (4), the mass ratio of the large-particle cobalt trioxide semi-finished product to the amorphous nano-cobalt carbonate is (10-15):1.

[0034] In one embodiment, in step (4), the secondary sintering temperature is 720-750° C., and the secondary sintering time is 2-4 hours.

[0035] In one embodiment, a method for preparing large particles of cobalt trioxide comprises the following steps:

[0036] (1) preparing a solution: preparing a cobalt salt solution, a precipitant solution A containing carbonate, a precipitant solution B and a precipitant solution C, and a precipitant solution D containing hydroxide, wherein the cobalt salt solution is one or more of a cobalt chloride solution, a cobalt nitrate solution and a cobalt sulfate solution, and the cobalt ion concentration in the cobalt salt solution is 1.5-2.0 mol / L; the precipitant solution A, the precipitant solution B and the precipitant solution C are one or more of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution and a potassium carbonate solution, the concentration of the precipitant solution A is 250-300 g / L, the concentration of the precipitant solution B is 60-120 g / L, and the concentration of the precipitant solution C is 160-240 g / L; the precipitant solution D is one or more of sodium hydroxide and potassium hydroxide, and the concentration is 320-480 g / L;

[0037] (2) Preparation of amorphous nano-cobalt carbonate: Precipitant solution A was added to the reactor as a base liquid, accounting for 50% of the reactor volume. The reaction temperature was controlled at 25-30°C, the stirring speed was 40-50 Hz, and the cobalt salt solution was passed through the reactor in a single flow. The reaction pH was controlled at 8.0-8.5. When the volume of the reactor liquid reached 80% of the effective volume, the liquid addition was stopped. The obtained slurry was completely discharged into a centrifuge for centrifugal dehydration, washed with pure water 3-5 times, and then dried and pulverized in a disc mill to obtain amorphous nano-cobalt carbonate with a D50 of less than 1 μm.

[0038] (3) Synthesis of cobalt carbonate matrix: add precipitant solution B as the bottom liquid in the reactor, accounting for 50% of the volume of the reactor, add a certain amount of cobalt salt solution and precipitant solution C in parallel at 38-45°C, keep the flow rate of the cobalt salt solution constant, adjust the flow rate of the precipitant solution C to control the synthesis pH to 7-8, stir at 15-20Hz, let the reactor stand after it is full, remove the supernatant, continue to add materials, and terminate the reaction when D50 reaches 15-16μm, add the amorphous nano-cobalt carbonate prepared in step (2) into the reactor and stir for 30-60min, wherein the added mass is 1 / 20-1 / 50 of the mass of the material in the reactor, to obtain a reaction solution containing a cobalt carbonate matrix coated with amorphous nano-cobalt carbonate;

[0039] (4) Synthesis of the cobalt hydroxide coating layer: The reactor of step (3) is continuously filled with an inert gas, wherein the inert gas is nitrogen or argon, and then a certain amount of precipitant solution D is pumped into the reaction solution of step (3), and the pH value of the bottom liquid is adjusted to 9.0-10.0, the temperature is 60-70°C, and the stirring frequency is 10-15 Hz. Then, the cobalt salt solution and the precipitant solution D are added in parallel, and the flow rate of the cobalt salt solution is kept constant. The flow rate of the precipitant solution D is adjusted to control the pH of the synthesis to 9-10, and the inert gas is continuously introduced. The reaction is terminated when the D50 reaches 18-20 μm. The material is filtered in a centrifuge to dry the mother liquor, and washed with pure water 3-5 times to obtain a cobalt carbonate / cobalt hydroxide mixture;

[0040] (5) Primary sintering: calcining the cobalt carbonate / cobalt hydroxide mixture obtained in step (4) at 350-450° C. in a box furnace for 2-4 h to obtain a large-particle cobalt oxide semi-finished product;

[0041] (6) Coating amorphous cobalt carbonate: The large-particle cobalt oxide semi-finished product obtained in step (5) and the amorphous cobalt carbonate obtained in step (2) are mixed thoroughly on a spiral mixer at a mass ratio of (10-15):1 for 30-60 minutes to obtain a sample of cobalt oxide-coated amorphous cobalt carbonate;

[0042] (7) Secondary sintering: The sample obtained in step (6) is calcined in a box furnace at 720-750° C. for 2-4 h to obtain a large-particle cobalt oxide product.

[0043] The beneficial effects of the present disclosure are:

[0044] (1) Cobalt hydroxide is synthesized in the form of an intercalated stack of hexagonal chips, which is usually loose and has a low tap density. After being sintered into cobalt tetroxide, it will also inherit its loose structure, which will ultimately affect the volume energy density of the positive electrode material; cobalt carbonate is synthesized in the form of a granular primary particle stacking growth mode, which is usually compact and has a high tap density. However, during the sintering process into cobalt tetroxide, if the carbon dioxide gas cannot be released in time, it will cause the internal stress of the particles to increase, resulting in the cracking and crushing of the spherical particles, affecting the processing performance of the material. The present invention synthesizes a large-particle mixed material with a core of cobalt carbonate and an outer shell of cobalt hydroxide, thereby ensuring the compactness of the core and making it have a higher tap density; at the same time, the flaky structure on the surface of the particles can provide a wider channel for the release of carbon dioxide gas generated during the thermal decomposition of the core cobalt carbonate, reducing the internal stress of the particles, completely releasing the gas under low-temperature sintering conditions, and avoiding particle damage. To address the relatively loose surface structure, the present invention first synthesizes amorphous cobalt carbonate and grinds and dries it using a disc-nest mill to improve its dispersibility. The amorphous cobalt carbonate is then fully mixed with a semi-finished cobalt oxide product after primary sintering in a certain proportion to fill the surface gaps. High-temperature sintering is then performed to fully decompose the amorphous cobalt carbonate coated on the surface and fuse and grow with the cobalt oxide matrix, thereby improving the overall crystallinity of the particles. Ultimately, large cobalt oxide particles with a complete surface, a dense core and an outer layer are prepared, and have a high tap density.

[0045] (2) The present disclosure adopts a positive addition method in the process of synthesizing amorphous cobalt carbonate: the cobalt salt solution is added separately to the solution with the carbonate-containing precipitant solution as the base liquid, which can increase the supersaturation at the moment of feeding and is conducive to the formation of amorphous cobalt carbonate.

[0046] (3) In order to make cobalt hydroxide uniformly coated on the cobalt carbonate matrix, the present invention utilizes the characteristics of amorphous nano-cobalt carbonate with high specific surface area, adsorption capacity and surface energy, and first coats it on the cobalt carbonate matrix. This not only improves the density of the cobalt carbonate matrix, fills surface defects, and further improves the tap density of the finished product, but also enables the cobalt carbonate matrix to have strong adsorption capacity and surface energy. In the early stage of synthesizing cobalt hydroxide, it helps the primary particles of cobalt hydroxide to be uniformly adsorbed and grown on the surface of the cobalt carbonate matrix, rather than cobalt hydroxide being nucleated alone in the system, so that the product has better consistency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] FIG1 is a SEM image of amorphous cobalt carbonate obtained in step (2) of Example 1 of the present disclosure;

[0048] FIG2 is a SEM image of the semi-finished large-particle cobalt trioxide obtained in step (5) of Example 1 of the present disclosure;

[0049] FIG3 is a SEM image of the large-particle cobalt tetroxide product obtained in Example 1 of the present disclosure;

[0050] FIG4 is an XRD pattern of the large-particle cobalt trioxide product obtained in Example 1 of the present disclosure;

[0051] FIG5 is a SEM image of the large-particle cobalt tetroxide product obtained in Comparative Example 1 of the present disclosure;

[0052] FIG6 is a SEM image of the coated cobalt hydroxide obtained in Comparative Example 2 of the present disclosure. DETAILED DESCRIPTION

[0053] The present disclosure is further described below with reference to specific embodiments.

[0054] Example 1:

[0055] A method for preparing large-particle cobalt trioxide comprises the following steps:

[0056] (1) Prepare the following solutions: 1.5 mol / L cobalt chloride solution, 250 g / L ammonium bicarbonate solution A, 60 g / L ammonium bicarbonate solution B, 160 g / L ammonium bicarbonate solution C, and 320 g / L sodium hydroxide solution D;

[0057] (2) Preparation of amorphous cobalt carbonate:

[0058] Ammonium bicarbonate solution A was added to the reactor as a base liquid, accounting for 50% of the reactor volume. The temperature was 25° C. and the stirring speed was 50 Hz. Cobalt chloride solution was introduced separately, and the flow rate of the cobalt chloride solution was adjusted to control the pH to 8.2. When the volume of the reactor liquid reached 80% of the effective volume, the liquid addition was stopped. The obtained slurry was discharged into a centrifuge for centrifugal dehydration, washed with pure water 5 times, and dried and pulverized in a disc nest mill to obtain amorphous cobalt carbonate with D50=0.82 μm. The SEM image of the obtained amorphous cobalt carbonate is shown in FIG1 . As can be seen from FIG1 , the obtained amorphous cobalt carbonate has good dispersibility.

[0059] (3) Cobalt carbonate matrix synthesis:

[0060] Add ammonium bicarbonate solution B as a bottom liquid in the reactor, accounting for 50% of the volume of the reactor, add 5L / h of cobalt chloride solution and ammonium bicarbonate solution C in parallel at 38°C, keep the flow rate of the cobalt chloride solution constant, adjust the flow rate of the ammonium bicarbonate solution C to control the pH value of the synthesis to 7.0, stir at 20Hz, let the reactor stand after it is full, remove the supernatant, continue to add materials, and terminate the reaction when D50 reaches 15.2μm, add the amorphous nano-cobalt carbonate prepared in step (2) into the reactor and stir for 30min, wherein the added mass is 1 / 30 of the mass of the material in the reactor, to obtain a reaction solution containing a cobalt carbonate matrix coated with amorphous nano-cobalt carbonate;

[0061] (4) Synthesis of cobalt hydroxide coating layer:

[0062] The reactor in step (3) was continuously charged with nitrogen, and then a certain amount of sodium hydroxide solution D was pumped into the reaction solution to adjust the bottom solution pH to 9.0, the temperature to 60° C., and the stirring frequency to 15 Hz. Then, the cobalt chloride solution and the sodium hydroxide solution D were flowed in parallel, the flow rate of the cobalt chloride solution was maintained at 5 L / h, and the flow rate of the sodium hydroxide solution D was adjusted to control the pH of the synthesis to 9.0. Nitrogen was continuously introduced during the parallel flow. The reaction was terminated when the D50 reached 18.3 μm. The material was filtered to dry the mother liquor in a centrifuge and washed three times to obtain a cobalt carbonate / cobalt hydroxide mixture;

[0063] (5) Primary sintering: The cobalt carbonate / cobalt hydroxide mixture obtained in step (4) was calcined in a box furnace at 350° C. for 4 h to obtain a large-particle cobalt oxide semi-finished product. The SEM image of the obtained large-particle cobalt oxide semi-finished product is shown in FIG2 . FIG2 shows that a large number of voids exist on the surface of the obtained large-particle cobalt oxide semi-finished product.

[0064] (6) Coated amorphous cobalt carbonate

[0065] The large-particle cobalt oxide semi-finished product obtained in step (5) and the amorphous cobalt carbonate obtained in step (2) are fully mixed in a spiral mixer at a mass ratio of 10:1 for 30 to 60 minutes to obtain a sample of cobalt oxide-coated amorphous cobalt carbonate;

[0066] (7) Secondary sintering: the sample obtained in step (6) was calcined at 750° C. in a box furnace for 4 h to obtain a large-particle cobalt tetroxide product. The SEM image of the obtained large-particle cobalt tetroxide product is shown in FIG3 , and the XRD pattern of the obtained large-particle cobalt tetroxide product is shown in FIG4 . It can be seen from FIG3 that the surface of the obtained large-particle cobalt tetroxide product is dense and smooth. FIG4 shows that the obtained large-particle cobalt tetroxide product is pure cobalt tetroxide with good crystallinity. The D50 of the obtained large-particle cobalt tetroxide product is 16.7 μm, and the tap density is 2.74 g / cm 3 , where the measurement standard for tap density is: GB / T 5162-2006.

[0067] Example 2:

[0068] A method for preparing large-particle cobalt trioxide comprises the following steps:

[0069] (1) Prepare the following solutions: 1.8 mol / L cobalt chloride solution, 300 g / L ammonium bicarbonate solution A, 80 g / L ammonium bicarbonate solution B, 200 g / L ammonium bicarbonate solution C, and 400 g / L sodium hydroxide solution D;

[0070] (2) Preparation of amorphous cobalt carbonate:

[0071] Ammonium bicarbonate solution A was added to the reactor as a base liquid, accounting for 50% of the reactor volume. The temperature was 30° C. and the stirring speed was 45 Hz. Cobalt chloride solution was introduced separately, and the flow rate of the cobalt chloride solution was adjusted to control the pH to 8.5. When the volume of the reactor liquid reached 80% of the effective volume, the liquid addition was stopped. The resulting slurry was discharged into a centrifuge for centrifugal dehydration, washed with pure water 5 times, and dried and pulverized in a disc mill to obtain amorphous cobalt carbonate with a D50 of 0.74 μm.

[0072] (3) Cobalt carbonate matrix synthesis:

[0073] Add ammonium bicarbonate solution B as a bottom liquid in the reactor, accounting for 50% of the volume of the reactor, add 50L / h of cobalt chloride solution and ammonium bicarbonate solution C in parallel at 41°C, keep the flow rate of the cobalt chloride solution constant, adjust the flow rate of ammonium bicarbonate solution C to control the pH of the synthesis to 7.5, stir at 18Hz, let the reactor stand after it is full, remove the supernatant, continue to feed, and terminate the reaction when D50 reaches 15.7μm, add the amorphous nano-cobalt carbonate prepared in step (2) into the reactor and stir for 60min, wherein the added mass is 1 / 20 of the mass of the material in the reactor, to obtain a reaction solution containing a cobalt carbonate matrix coated with amorphous nano-cobalt carbonate;

[0074] (4) Synthesis of cobalt hydroxide coating layer:

[0075] The reactor in step (3) is continuously filled with argon, and then a certain amount of sodium hydroxide solution D is pumped into the reaction solution to adjust the bottom liquid pH to 9.5, the temperature to 65° C., and the stirring frequency to 13 Hz. Then, the cobalt chloride solution and the sodium hydroxide solution D are flowed in parallel, the flow rate of the cobalt chloride solution is maintained at 50 L / h, and the flow rate of the sodium hydroxide solution D is adjusted to control the synthesized pH to 9.5. Argon is continuously introduced during the parallel flow, and the reaction is terminated when the D50 reaches 19.2 μm. The material is filtered and the mother liquor is dried in a centrifuge and washed 5 times to obtain a cobalt carbonate / cobalt hydroxide mixture;

[0076] (5) Primary sintering: calcining the cobalt carbonate / cobalt hydroxide mixture obtained in step (4) in a box furnace at 400° C. for 4 h to obtain a large-particle cobalt trioxide semi-finished product;

[0077] (6) Coated amorphous cobalt carbonate

[0078] The large-particle cobalt oxide semi-finished product obtained in step (5) and the amorphous cobalt carbonate obtained in step (2) were fully mixed on a spiral mixer at a mass ratio of 12:1 for 50 minutes to obtain a sample of cobalt oxide-coated amorphous cobalt carbonate;

[0079] (7) Secondary sintering: the sample obtained in step (6) was calcined in a box furnace at 730°C for 4 hours to obtain a large-particle cobalt tetroxide product. The obtained large-particle cobalt tetroxide product had a D50 of 16.7 μm and a tap density of 2.69 g / cm 3 ;

[0080] Comparative Example 1:

[0081] A method for preparing large-particle cobalt trioxide comprises the following steps:

[0082] (1) Prepare the following solutions: 1.5 mol / L cobalt chloride solution, 60 g / L ammonium bicarbonate solution A, and 160 g / L ammonium bicarbonate solution B;

[0083] (2) Cobalt carbonate synthesis:

[0084] A 60 g / L ammonium bicarbonate solution A was added to the reactor as a bottom liquid, accounting for 50% of the volume of the reactor. A 5 L / h cobalt chloride solution and an ammonium bicarbonate solution B were added in parallel at 38° C., while maintaining the flow rate of the cobalt chloride solution constant. The flow rate of the ammonium bicarbonate solution B was adjusted to control the pH value to 7.0. The stirring frequency was 20 Hz. After the reactor was full, the mixture was allowed to stand, and after removing the supernatant, the mixture was continued to be fed until the D50 value reached 18.4 μm. The reaction was terminated, and the mother liquor was filtered out in a centrifuge to obtain large-particle cobalt carbonate.

[0085] (3) Calcination

[0086] The large-particle cobalt carbonate obtained in the above step (2) was calcined at 720° C. in a box furnace for 4 h to obtain a large-particle cobalt tetroxide product. The SEM image of the obtained large-particle cobalt tetroxide product is shown in FIG5 , which shows that the particles are cracked and de-powdered. The D50 of the obtained large-particle cobalt tetroxide product is 16.4 μm and the tap density is 2.10 g / cm 3 .

[0087] Comparative Example 2: (The only difference from Example 1 is that amorphous nano-cobalt carbonate is not coated in step (3))

[0088] A method for preparing large-particle cobalt trioxide comprises the following steps:

[0089] (1) Prepare the following solutions: 1.5 mol / L cobalt chloride solution, 250 g / L ammonium bicarbonate solution A, 60 g / L ammonium bicarbonate solution B, 160 g / L ammonium bicarbonate solution C, and 320 g / L sodium hydroxide solution D;

[0090] (2) Preparation of amorphous cobalt carbonate:

[0091] Ammonium bicarbonate solution A was added to the reactor as a base liquid, accounting for 50% of the reactor volume. The temperature was maintained at 25° C. and the stirring speed was 50 Hz. Cobalt chloride solution was introduced separately, and the flow rate of the cobalt chloride solution was adjusted to control the pH to 8.2. When the volume of the reactor liquid reached 80% of the effective volume, the liquid addition was stopped. The resulting slurry was discharged into a centrifuge for centrifugal dehydration, washed with pure water 5 times, and dried and pulverized in a disc mill to obtain amorphous cobalt carbonate with a D50 of 0.82 μm.

[0092] (3) Cobalt carbonate matrix synthesis:

[0093] Add ammonium bicarbonate solution B as a base liquid to the reactor, accounting for 50% of the volume of the reactor, and add 5 L / h of cobalt chloride solution and ammonium bicarbonate solution C in parallel at 38° C., maintaining the flow rate of the cobalt chloride solution constant, adjusting the flow rate of the ammonium bicarbonate solution C to control the synthesized pH to 7.0, and stirring at a frequency of 20 Hz. After the reactor is full, let it stand, remove the supernatant, and continue adding materials. The reaction is terminated when the D50 reaches 15.2 μm to obtain a reaction solution containing a cobalt carbonate matrix;

[0094] (4) Synthesis of cobalt hydroxide coating layer:

[0095] The reactor in step (3) is continuously filled with nitrogen, and then a certain amount of sodium hydroxide solution D is pumped into the reaction solution to adjust the bottom liquid pH to 9.0, the temperature to 60° C., and the stirring frequency to 15 Hz. Then, the cobalt chloride solution and the sodium hydroxide solution D are flowed in parallel, the flow rate of the cobalt chloride solution is maintained at 5 L / h, and the flow rate of the sodium hydroxide solution D is adjusted to control the pH of the synthesis to 9.0. Nitrogen is continuously introduced during the parallel flow. The reaction is terminated when the D50 reaches 18.3 μm. The material is filtered and the mother liquor is dried in a centrifuge and washed three times to obtain a cobalt carbonate / cobalt hydroxide mixture;

[0096] (5) Primary sintering: The cobalt carbonate / cobalt hydroxide mixture obtained in step (4) was calcined in a box furnace at 350° C. for 4 h to obtain a large-particle cobalt oxide semi-finished product. The SEM image of the obtained large-particle cobalt oxide semi-finished product is shown in FIG6 , which shows that cobalt hydroxide is independently nucleated in the obtained large-particle cobalt oxide semi-finished product;

[0097] (6) Coated amorphous cobalt carbonate

[0098] The large-particle cobalt oxide semi-finished product obtained in step (5) and the amorphous cobalt carbonate obtained in step (2) are fully mixed in a spiral mixer at a mass ratio of 10:1 for 30 to 60 minutes to obtain a sample of cobalt oxide-coated amorphous cobalt carbonate;

[0099] (7) Secondary sintering: the sample obtained in step (6) was calcined in a box furnace at 750°C for 4 hours to obtain a large-particle cobalt tetroxide product with a D50 of 15.8 μm and a tap density of 2.4 g / cm 3 .

Claims

1. A method for preparing large-particle cobalt trioxide, characterized in that: The following steps are involved: (1) mixing a cobalt salt solution with a precipitant solution A containing carbonate, separating the solid and the liquid after the reaction, drying and crushing the solid phase to obtain amorphous nano-cobalt carbonate; (2) mixing the cobalt salt solution with the precipitant solution B containing carbonate and the precipitant solution C containing carbonate to react and generate cobalt carbonate particles, and then adding the amorphous nano-cobalt carbonate prepared in step (1) to react and obtain a reaction solution containing a cobalt carbonate matrix coated with the amorphous nano-cobalt carbonate; (3) under an inert atmosphere, adding a precipitant solution D containing hydroxide to the reaction solution of step (2) to adjust the pH to neutral or alkaline, then adding a cobalt salt solution and a precipitant solution D containing hydroxide, reacting to generate mixed particles, separating the solid and the liquid, taking the solid phase to obtain a cobalt carbonate / cobalt hydroxide mixture, and sintering once to obtain a large particle cobalt oxide semi-finished product; (4) mixing the large-particle cobalt oxide semi-finished product obtained in step (3) with the amorphous nano-cobalt carbonate obtained in step (1), and performing secondary sintering to obtain large-particle cobalt oxide.

2. The method for preparing large-particle cobalt tetroxide according to claim 1, characterized in that: The cobalt salt solution is at least one of a cobalt chloride solution, a cobalt nitrate solution and a cobalt sulfate solution.

3. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: The concentration of cobalt ions in the cobalt salt solution is 1.5-2.0 mol / L.

4. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: The precipitant solution A is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution and a potassium carbonate solution, and the concentration of the precipitant solution A is 250-300 g / L.

5. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: The precipitant solution B is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution and a potassium carbonate solution, and the concentration of the precipitant solution B is 60-120 g / L.

6. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: The precipitant solution C is at least one of a sodium carbonate solution, a potassium bicarbonate solution, a sodium bicarbonate solution and a potassium carbonate solution, and the concentration of the precipitant solution C is 160-240 g / L.

7. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: The precipitant solution D is at least one of a sodium hydroxide solution and a potassium hydroxide solution, and the concentration of the precipitant solution D is 320-480 g / L.

8. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (1), the cobalt salt solution is mixed with the precipitant solution A containing carbonate, with the precipitant solution A as the base solution, and then the cobalt salt solution is added.

9. The method for preparing large-particle cobalt trioxide according to claim 8, characterized in that: In step (1), the cobalt salt solution is added gradually under stirring.

10. The method for preparing large-particle cobalt trioxide according to claim 9, characterized in that: In step (1), the stirring speed is 40-50 Hz.

11. The method for preparing large-particle cobalt trioxide according to claim 10, characterized in that: In step (1), the reaction temperature is 25-30°C.

12. The method for preparing large-particle cobalt trioxide according to claim 11, characterized in that: In step (1), the pH of the reaction is 8.0-8.

5.

13. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (1), the drying and crushing is carried out using a disc-nest mill.

14. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (1), the D50 of the amorphous nano-cobalt carbonate is less than 1 μm.

15. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (2), the cobalt salt solution is mixed with the precipitant solution B containing carbonate and the precipitant solution C containing carbonate, with the precipitant solution B as the base solution, and then the cobalt salt solution and the precipitant solution C containing carbonate are added.

16. The method for preparing large-particle cobalt trioxide according to claim 15, characterized in that: In step (2), the adding of the cobalt salt solution and the precipitant solution C containing carbonate refers to first adding the cobalt salt solution and the precipitant solution C in parallel at 38-45° C., then keeping the flow rate of the cobalt salt solution unchanged, adjusting the flow rate of the precipitant solution C to control the synthesized pH to 7-8, and controlling the stirring frequency to 15-20 Hz to generate cobalt carbonate particles with a D50 of 15-16 μm.

17. The method for preparing large-particle cobalt trioxide according to claim 16, characterized in that: In step (2), the mass of the amorphous nano-cobalt carbonate added is 1 / 20-1 / 50 of the total mass of the cobalt carbonate particles and the amorphous nano-cobalt carbonate.

18. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (3), after adding the precipitant solution B containing hydroxide to the reaction solution of step (2), the reaction temperature is controlled to be 60-70° C. and the stirring frequency is controlled to be 10-15 Hz.

19. The method for preparing large-particle cobalt trioxide according to claim 18, characterized in that: In step (3), the pH is adjusted to 9-10.

20. The method for preparing large-particle cobalt trioxide according to claim 19, characterized in that: In step (3), adding the cobalt salt solution and the precipitant solution D means first adding the cobalt salt solution and the precipitant solution D in parallel, then keeping the flow rate of the cobalt salt solution unchanged, and adjusting the flow rate of the precipitant solution D to control the synthesized pH to 9-10 to generate mixed particles with a D50 of 18-20 μm.

21. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (3), the primary sintering temperature is 350-450° C., and the primary sintering time is 2-4 hours.

22. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (4), the mass ratio of the large-particle cobalt oxide semi-finished product to the amorphous nano-cobalt carbonate is (10-15):

1.

23. The method for preparing large-particle cobalt trioxide according to claim 1, characterized in that: In step (4), the secondary sintering temperature is 720-750° C., and the secondary sintering time is 2-4 hours.

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