A preparation method of flaky cobalt hydroxide

Abstract

The present disclosure relates to a method for preparing flaky cobalt hydroxide. The preparation method includes the following steps: mixing a precipitant, a cobalt salt solution, and humic acid and performing a precipitation reaction to obtain a slurry; subjecting the slurry to solid-liquid separation, and sequentially washing and drying the separated solid to obtain flaky cobalt hydroxide. The preparation method provided by the present disclosure can prepare flaky cobalt hydroxide with good dispersion and no oxidation, and there is no need for an additional crushing step in the operation process, saving costs and being safe and non-toxic.

Description

Technical Field

[0001] The present disclosure relates to the technical field of metal oxide materials, and particularly to a method for preparing flaky cobalt hydroxide. Background Art

[0002] High-nickel ternary cathode materials have advantages such as high energy density, good rate performance, and long life, and have received wide attention in the field of lithium-ion batteries. At present, an excessive amount of lithium source is usually added during the preparation process of high-nickel ternary cathode materials to make up for the loss of lithium during the sintering process, which in turn leads to the residual of Li2O on the surface of the obtained cathode material. The residual Li2O easily reacts with H2O and CO2 in the atmosphere to form Li2CO3 / LiOH adhering to the surface of the material, and during the charge and discharge process, Li2CO3 / LiOH reacts with the electrolyte to generate CO2, resulting in the expansion and explosion inside the battery.

[0003] Related research has found that coating cobalt hydroxide on the surface of high-nickel ternary cathode materials can not only effectively reduce the residual amount of lithium, but also form a cobalt-rich concentration gradient layer on the surface of the cathode material, thereby improving the cycle performance of the material. However, if the longitudinal size of the cobalt hydroxide wrapped on the surface of the cathode material is too large, it will lead to a high impedance of the cathode material, thereby reducing the electrochemical performance. Therefore, flaky cobalt hydroxide is a better choice for preparing high-nickel cathode materials. However, during the preparation process of flaky cobalt hydroxide materials, there are double problems of particle agglomeration and material oxidation. On the one hand, it is necessary to be processed by crushing equipment such as a disk nest mill and a jet mill to avoid product agglomeration, which not only has a high cost, but also easily causes dust pollution; on the other hand, it is necessary to add a reducing agent to avoid the oxidation of cobalt hydroxide, but the commonly used reducing agents are toxic and flammable, bringing great potential safety hazards.

[0004] For example, CN104261489A discloses a hexagonal β-cobalt hydroxide nanosheet and a preparation method thereof. In this method, ethylene glycol, methanol, and an alkali are mixed to prepare a system solvent, and then a water-soluble cobalt salt and hydrazine hydrate are added to the system to prepare flaky cobalt hydroxide. In the above method, not only is the used hydrazine hydrate highly toxic, but also the obtained flaky cobalt hydroxide cannot achieve a good dispersion effect.

[0005] Therefore, how to safely and economically prepare well-dispersed and non-oxidized flaky cobalt hydroxide is an urgent problem to be solved currently. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of protection of the claims.

[0007] In response to the above problems, the purpose of the present disclosure is to provide a method for preparing flaky cobalt hydroxide. Compared with related technologies, the preparation method provided by the present disclosure can prepare well-dispersed and non-oxidized flaky cobalt hydroxide, and the operation process does not require additional crushing steps, which saves costs and is safe and non-toxic.

[0008] To achieve this disclosure purpose, the embodiments of the present disclosure adopt the following technical solutions:

[0009] The present disclosure provides a method for preparing flaky cobalt hydroxide, the method comprising the following steps:

[0010] A precipitant, a cobalt salt solution and humic acid are mixed and subjected to precipitation reaction to obtain a slurry; the slurry is subjected to solid-liquid separation, and the separated solid is sequentially washed and dried to obtain flaky cobalt hydroxide.

[0011] The disclosed embodiment adds humic acid to the reaction system, and humic acid is both a dispersant and an antioxidant and a chelating agent during the reaction. The role of humic acid is specifically as follows: First, humic acid is used as an organic macromolecule to be attached to the surface of the cobalt hydroxide nanosheet by adsorption or covalent bonding to form an organic protective layer, which can effectively increase the steric hindrance between the nanoparticles, thereby inhibiting the agglomeration between the cobalt hydroxide nanosheets; second, the surface charge of the cobalt hydroxide particles is affected by the carboxyl, hydroxyl and ketone carbonyl groups of humic acid, thereby improving the stability of the cobalt hydroxide nanosheets in the environment, and further inhibiting the spontaneous agglomeration of the cobalt hydroxide nanosheets; third, the antioxidant property of humic acid is used to avoid the risk of cobalt hydroxide being oxidized and deteriorated during the synthesis process; fourth, humic acid is used to chelate with cobalt ions to affect the growth direction of cobalt, promote lateral growth, and inhibit longitudinal growth, thereby showing a lamellar morphology. Through the effects of the above four aspects, the cobalt hydroxide obtained by the preparation method described in the disclosed embodiment not only has an excellent lamellar structure, but also has good dispersibility and no oxidative deterioration.

[0012] In one embodiment, the humic acid is added to the mixing in the form of a humic acid solution.

[0013] In the disclosed embodiment, since humic acid is insoluble in water, in order to promote mixing and avoid direct reaction between humic acid and the precipitant, humic acid is first dissolved to prepare a humic acid-containing solution, and then mixed, which can improve the reaction effect.

[0014] In one embodiment, a reaction base liquid is further added into the mixing.

[0015] In one embodiment, the reaction base liquid is added into the reaction kettle in advance.

[0016] In one embodiment, the volume of the reaction bottom liquid accounts for 30-60% of the volume of the reaction kettle. For example, it can be 30%, 35%, 40%, 45%, 50%, 55% or 60%, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0017] In the embodiments of the present disclosure, it is preferred to control the percentage content of the volume of the reaction bottom liquid in the volume of the reaction kettle within a specific range, which can provide suitable pH reaction conditions for the precipitation reaction in advance.

[0018] In one embodiment, the mixing method includes: adding a precipitant, a cobalt salt solution and a humic acid-containing solution to the reaction bottom liquid simultaneously.

[0019] In one embodiment, the flow rate of the cobalt salt solution when added is 10-1200 L / h. For example, it can be 10 L / h, 50 L / h, 100 L / h, 200 L / h, 400 L / h, 600 L / h, 800 L / h, 1000 L / h or 1200 L / h, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0020] In one embodiment, the reaction bottom liquid includes a sodium hydroxide solution.

[0021] In one embodiment, the concentration of sodium hydroxide in the reaction bottom liquid is 100-400 g / L. For example, it can be 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L or 400 g / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0022] In one embodiment, the solvent of the humic acid-containing solution includes a sodium hydroxide solution.

[0023] In one embodiment, the concentration of sodium hydroxide in the humic acid-containing solution is 10-40 g / L. For example, it can be 10 g / L, 15 g / L, 20 g / L, 25 g / L, 30 g / L, 35 g / L or 40 g / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0024] In one embodiment, the precipitant includes a sodium hydroxide solution.

[0025] In one embodiment, the concentration of sodium hydroxide in the precipitant is 100-400 g / L. For example, it can be 100 g / L, 150 g / L, 200 g / L, 250 g / L, 300 g / L, 350 g / L or 400 g / L, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0026] In one embodiment, the cobalt salt solution contains any one or a combination of at least two of cobalt chloride, cobalt sulfate, or cobalt nitrate. Typical but non-limiting combinations include a combination of cobalt chloride and cobalt sulfate or a combination of cobalt chloride and cobalt nitrate.

[0027] In one embodiment, the concentration of cobalt element in the cobalt salt solution is 90 - 130 g / L. For example, it can be 90 g / L, 95 g / L, 100 g / L, 105 g / L, 110 g / L, 115 g / L, 120 g / L, 125 g / L, or 130 g / L. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0028] In one embodiment, the mass of humic acid in the mixture accounts for 0.03 - 0.3% of the mass of cobalt element in the cobalt salt solution. For example, it can be 0.03%, 0.04%, 0.06%, 0.08%, 0.1%, 0.12%, 0.14%, 0.16%, 0.18%, 0.2%, 0.22%, 0.24%, 0.26%, 0.28%, or 0.3%. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0029] In the embodiments of the present disclosure, it is preferably to control the percentage of the mass of humic acid in the mass of cobalt element within a specific range. On the one hand, it is beneficial to obtain flaky cobalt hydroxide with good dispersibility and no oxidation. On the other hand, it can avoid excessive content of organic matter in cobalt hydroxide, which increases the difficulty of subsequent treatment.

[0030] In one embodiment, stirring is carried out during the precipitation reaction.

[0031] In one embodiment, the stirring rate is 200 - 700 r / min. For example, it can be 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min, 500 r / min, 550 r / min, 600 r / min, 650 r / min, or 700 r / min. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0032] In one embodiment, the temperature of the precipitation reaction is 25 - 50 °C. For example, it can be 25 °C, 28 °C, 30 °C, 32 °C, 35 °C, 38 °C, 40 °C, 42 °C, 45 °C, 48 °C, or 50 °C. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0033] In one embodiment, the pH value of the reaction system in the precipitation reaction is controlled by the addition amount of the precipitant.

[0034] In the embodiments of the present disclosure, as the precipitation reaction proceeds, cobalt ions continuously combine with hydroxide ions to form cobalt hydroxide, resulting in a change in the pH value of the reaction system. In the embodiments of the present disclosure, the pH value of the reaction system can be controlled by adding a precipitating agent to maintain the pH value under suitable reaction conditions.

[0035] In one embodiment, the pH value of the reaction system is 11 - 13. For example, it can be 11, 11.5, 12, 12.5, 13, or 13.5, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0036] The embodiments of the present disclosure preferably control the pH value of the reaction system within a specific range, which can further promote the formation of flaky cobalt hydroxide.

[0037] In one embodiment, nitrogen is introduced during the precipitation reaction.

[0038] In one embodiment, the flow rate of the nitrogen is 0.5 - 30 L / min. For example, it can be 0.5 L / min, 1 L / min, 2 L / min, 5 L / min, 8 L / min, 10 L / min, 12 L / min, 15 L / min, 18 L / min, 20 L / min, 22 L / min, 25 L / min, 28 L / min, or 30 L / min, but is not limited to the listed values. Other unlisted values within the numerical range are equally applicable.

[0039] In the embodiments of the present disclosure, it is preferred to introduce nitrogen during the precipitation reaction, which can remove the air in the system and prevent cobalt hydroxide from contacting with air and undergoing oxidation. In the preparation method provided by the embodiments of the present disclosure, adding humic acid can play an antioxidant role. Therefore, compared with the current cobalt hydroxide preparation process, the amount of nitrogen introduced in the preparation method provided by the embodiments of the present disclosure is significantly reduced.

[0040] In one embodiment, the method of solid-liquid separation includes filtration.

[0041] In one embodiment, the washing liquid used for washing includes ammonium bicarbonate solution or ammonia water.

[0042] In the embodiments of the present disclosure, it is preferred to use a washing liquid including ammonium bicarbonate solution or ammonia water because ammonium bicarbonate or ammonia water can decompose into ammonia, carbon dioxide, and water vapor during the drying process, thereby destroying the agglomeration between particles and effectively omitting the crushing step of cobalt hydroxide.

[0043] In one embodiment, the concentration of the washing solution is 5 - 30 g / L. For example, it can be 5 g / L, 8 g / L, 10 g / L, 12 g / L, 15 g / L, 18 g / L, 20 g / L, 22 g / L, 25 g / L, 28 g / L, or 30 g / L. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0044] In one embodiment, humic acid is further added to the washing solution.

[0045] In the embodiments of the present disclosure, it is preferred to add humic acid to the washing solution because cobalt hydroxide is easily oxidized during the washing process, and humic acid can reduce the partially oxidized cobalt hydroxide to achieve the purpose of ensuring product quality.

[0046] In one embodiment, the addition amount of humic acid in the washing solution is 0.03 - 0.3 g / L. For example, it can be 0.03 g / L, 0.04 g / L, 0.06 g / L, 0.08 g / L, 0.1 g / L, 0.12 g / L, 0.14 g / L, 0.16 g / L, 0.18 g / L, 0.2 g / L, 0.22 g / L, 0.24 g / L, 0.26 g / L, 0.28 g / L, or 0.3 g / L. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0047] In the embodiments of the present disclosure, it is preferred to control the addition amount of humic acid in the washing solution within a specific range. On the one hand, it is beneficial to obtain flaky cobalt hydroxide with good dispersibility and no oxidation. On the other hand, it can avoid excessive content of organic matter in cobalt hydroxide, increasing the difficulty of subsequent treatment.

[0048] In one embodiment, the number of washing times ≥ 3 times. For example, it can be 3 times, 4 times, or 5 times. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0049] In one embodiment, the volume of the washing solution used for each washing is 0.5 - 1.5 times the volume of the slurry. For example, it can be 0.5 times, 1 times, or 1.5 times. However, it is not limited to the listed values, and other unlisted values within the numerical range are equally applicable.

[0050] As an alternative technical solution of the embodiments of the present disclosure, the preparation method includes the following steps:

[0051] Using a sodium hydroxide solution with a concentration of 100 - 400 g / L as the reaction bottom solution, a sodium hydroxide solution with a concentration of 100 - 400 g / L as the precipitant, controlling the concentration of cobalt element in the cobalt salt solution to be 90 - 130 g / L, the concentration of sodium hydroxide in the humic acid-containing solution to be 10 - 40 g / L, and the mass of humic acid accounting for 0.03 - 0.3% of the mass of cobalt element in the cobalt salt solution;

[0052] Pre-add the reaction bottom liquid into the reaction kettle, where the volume of the reaction bottom liquid accounts for 30 - 60% of the volume of the reaction kettle. Then, add a precipitant, a cobalt salt solution, and a humic acid-containing solution to the reaction bottom liquid. Control the flow rate of the cobalt salt solution during addition to be 10 - 1200 L / h, and control the addition amount of the precipitant to make the pH value of the reaction system be 11 - 13. Conduct a precipitation reaction under the conditions of a temperature of 25 - 50 °C, a nitrogen flow rate of 0.5 - 30 L / min, and a stirring rate of 200 - 700 r / min to obtain a slurry;

[0053] Filter the said slurry, wash the obtained solid with a washing liquid ≥3 times, and then dry it to obtain flaky cobalt hydroxide;

[0054] The volume of the washing liquid used for each washing is 0.5 - 1.5 times the volume of the slurry. The washing liquid includes an ammonium bicarbonate solution or ammonia water. The concentration of the washing liquid is 5 - 30 g / L, and the concentration of humic acid in the washing liquid is 0.03 - 0.3 g / L.

[0055] Compared with the related technology, the present disclosure has the following beneficial effects:

[0056] (1) In the preparation method provided by the present disclosure, humic acid is adsorbed or covalently bonded to the surface of cobalt hydroxide, which can form steric hindrance to avoid the agglomeration of flaky cobalt hydroxide particles. Moreover, functional groups such as carboxyl, hydroxyl, and ketone carbonyl groups contained in humic acid affect the surface charge of cobalt hydroxide particles, promoting the stability of cobalt hydroxide in the environment and further inhibiting the agglomeration of flaky cobalt hydroxide, thereby achieving a good dispersion effect.

[0057] (2) The preparation method provided by the present disclosure also utilizes the antioxidant property of humic acid to avoid the oxidation and deterioration of cobalt hydroxide during the preparation process. Moreover, humic acid is safe, non-toxic, inexpensive, and easily available, improving the economy and safety of production.

[0058] (3) In the preparation method provided by the present disclosure, chelation occurs between humic acid and cobalt ions, which can promote the lateral growth of cobalt hydroxide and inhibit the longitudinal growth, thereby obtaining flaky cobalt hydroxide with excellent structure. The I(001) / I(100) value of the obtained cobalt hydroxide reaches above 3.42, and can reach above 6.11 under better conditions.

[0059] (4) In the preparation method provided by the present disclosure, using an ammonium bicarbonate solution or ammonia water as the washing liquid can break the agglomeration of the product during the drying process, avoid adding an additional crushing step, simplify the operation process, and reduce the production cost.

[0060] Other aspects can be understood after reading and understanding the drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] The accompanying drawings are used to provide a further understanding of the technical solutions herein, and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solutions herein, and do not constitute a limitation to the technical solutions herein.

[0062] Figure 1 It is the SEM image of cobalt hydroxide obtained in Example 1 of the present disclosure;

[0063] Figure 2 It is the SEM image of cobalt hydroxide obtained in Example 2 of the present disclosure;

[0064] Figure 3 It is the SEM image of cobalt hydroxide obtained in Example 3 of the present disclosure;

[0065] Figure 4 It is the SEM image of cobalt hydroxide obtained in Example 4 of the present disclosure;

[0066] Figure 5 It is the SEM image of cobalt hydroxide obtained in Example 5 of the present disclosure;

[0067] Figure 6 It is the SEM image of cobalt hydroxide obtained in Example 6 of the present disclosure;

[0068] Figure 7 It is the SEM image of cobalt hydroxide obtained in Example 7 of the present disclosure;

[0069] Figure 8 It is the SEM image of cobalt hydroxide obtained in Example 8 of the present disclosure;

[0070] Figure 9 It is the SEM image of cobalt hydroxide obtained in Example 9 of the present disclosure;

[0071] Figure 10 It is the SEM image of cobalt hydroxide obtained in Example 10 of the present disclosure;

[0072] Figure 11 It is the SEM image of cobalt hydroxide obtained in Comparative Example 1 of the present disclosure;

[0073] Figure 12 It is the XRD pattern of cobalt hydroxide obtained in Examples 1-4 and Examples 7-8 of the present disclosure. Detailed Embodiments

[0074] The technical solutions of the present disclosure will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only for helping to understand the present disclosure and should not be regarded as specific limitations to the present disclosure.

[0075] Example 1

[0076] This example provides a method for preparing flaky cobalt hydroxide, and the preparation method includes the following steps:

[0077] Using a sodium hydroxide solution with a concentration of 100 g / L as the reaction bottom liquid, a sodium hydroxide solution with a concentration of 100 g / L as the precipitant, a cobalt chloride solution as the cobalt salt solution, controlling the concentration of cobalt element in the cobalt salt solution to be 90 g / L, the concentration of sodium hydroxide in the humic acid-containing solution to be 10 g / L, and the mass of humic acid to account for 0.03% of the mass of cobalt element in the cobalt salt solution;

[0078] Pre-add the reaction bottom liquid into the reaction kettle, with the volume of the reaction bottom liquid accounting for 30% of the volume of the reaction kettle. Simultaneously add the precipitant, cobalt salt solution, and humic acid-containing solution to the reaction bottom liquid. Control the flow rate of the cobalt salt solution during addition to be 10 L / h, control the addition amount of the precipitant to make the pH value of the reaction system 11, and carry out the precipitation reaction at a temperature of 25 °C, a nitrogen flow rate of 0.5 L / min, and a stirring rate of 200 r / min until the reaction liquid level reaches the overflow port of the reaction kettle to stop the reaction, obtaining a slurry;

[0079] Filter the slurry, wash the filtered solid 3 times with a washing liquid, and then dry it to obtain flaky cobalt hydroxide;

[0080] The volume of the washing liquid used for each washing is 0.5 times the volume of the slurry, and the washing liquid is 5 g / L ammonia water with humic acid added at an amount of 0.03 g / L.

[0081] The SEM image of the cobalt hydroxide obtained in this example is as Figure 1 shown. It can be seen from Figure 1 that the cobalt hydroxide has a flaky structure, with a primary particle size of 90 - 100 nm and a thickness of approximately 32 nm.

[0082] Example 2

[0083] This example provides a method for preparing flaky cobalt hydroxide, and the preparation method includes the following steps:

[0084] Using a sodium hydroxide solution with a concentration of 400 g / L as the reaction bottom liquid, a sodium hydroxide solution with a concentration of 400 g / L as the precipitant, a cobalt chloride solution as the cobalt salt solution, controlling the concentration of cobalt element in the cobalt salt solution to be 130 g / L, the concentration of sodium hydroxide in the humic acid-containing solution to be 40 g / L, and the mass of humic acid to account for 0.3% of the mass of cobalt element in the cobalt salt solution;

[0085] Pre-add the reaction bottom liquid into the reaction kettle. The volume of the reaction bottom liquid accounts for 60% of the volume of the reaction kettle. Add a precipitant, a cobalt salt solution, and a humic acid-containing solution to the reaction bottom liquid simultaneously. Control the flow rate of the cobalt salt solution during addition to be 1200 L / h. Control the addition amount of the precipitant to make the pH value of the reaction system 13. Conduct a precipitation reaction under the conditions of a temperature of 50 °C, a nitrogen flow rate of 30 L / min, and a stirring rate of 700 r / min until the reaction liquid level reaches the overflow port of the reaction kettle to stop the reaction, obtaining a slurry;

[0086] Filter the said slurry. Wash the filtered solid with a washing liquid 3 times, and then dry it to obtain flaky cobalt hydroxide;

[0087] The volume of the washing liquid used each time is 1.5 times the volume of the slurry. The washing liquid is a 30 g / L ammonium bicarbonate solution and humic acid is added to the ammonium bicarbonate solution at an addition amount of 0.3 g / L.

[0088] The SEM image of the cobalt hydroxide obtained in this example is as Figure 2 shown. From Figure 2 it can be seen that the cobalt hydroxide has a flaky structure, the primary particle size is 100 - 120 nm, and the thickness is about 25 nm.

[0089] Example 3

[0090] This example provides a preparation method of flaky cobalt hydroxide. The preparation method includes the following steps:

[0091] Use a sodium hydroxide solution with a concentration of 200 g / L as the reaction bottom liquid, a sodium hydroxide solution with a concentration of 200 g / L as the precipitant, a cobalt nitrate solution as the cobalt salt solution. Control the concentration of cobalt element in the cobalt salt solution to be 100 g / L, the concentration of sodium hydroxide in the humic acid-containing solution to be 20 g / L, and the mass of humic acid to account for 0.2% of the mass of cobalt element in the cobalt salt solution;

[0092] Pre-add the reaction bottom liquid into the reaction kettle. The volume of the reaction bottom liquid accounts for 50% of the volume of the reaction kettle. Add a precipitant, a cobalt salt solution, and a humic acid-containing solution to the reaction bottom liquid simultaneously. Control the flow rate of the cobalt salt solution during addition to be 800 L / h. Control the addition amount of the precipitant to make the pH value of the reaction system 12, and conduct a precipitation reaction under the conditions of a temperature of 40 °C, a nitrogen flow rate of 10 L / min, and a stirring rate of 500 r / min until the reaction liquid level reaches the overflow port of the reaction kettle to stop the reaction, obtaining a slurry;

[0093] Filter the said slurry. Wash the filtered solid with a washing liquid 3 times, and then dry it to obtain flaky cobalt hydroxide;

[0094] The volume of the washing solution used for each washing is 1 time the volume of the slurry. The washing solution is an ammonium bicarbonate solution with a concentration of 20 g / L, and humic acid is added to the ammonium bicarbonate solution at an addition amount of 0.2 g / L.

[0095] The SEM image of the cobalt hydroxide obtained in this example is as Figure 3 shown. From Figure 3 it can be seen that the cobalt hydroxide has a flaky structure, the primary particle size is 100 - 110 nm, and the thickness is about 30 nm.

[0096] Example 4

[0097] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that the mass of humic acid accounts for 0.01% of the mass of cobalt element in the cobalt salt solution.

[0098] The SEM image of the cobalt hydroxide obtained in this example is as Figure 4 shown. From Figure 4 it can be seen that the flaky structure of the cobalt hydroxide is not obvious, and there is a phenomenon of adhesion between some particles, mainly because oxidation occurs during the reaction to generate cobalt oxyhydroxide.

[0099] Example 5

[0100] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that the addition amount of the precipitant is controlled to make the pH value of the reaction system 10.

[0101] The SEM image of the cobalt hydroxide obtained in this example is as Figure 5 shown. From Figure 5 it can be seen that the cobalt hydroxide has a flaky structure, but the sizes are uneven.

[0102] Example 6

[0103] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that the addition amount of the precipitant is controlled to make the pH value of the reaction system 14.

[0104] The SEM image of the cobalt hydroxide obtained in this example is as Figure 6 shown. From Figure 6 it can be seen that the cobalt hydroxide has a flaky structure, but some products agglomerate.

[0105] Example 7

[0106] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that the addition amount of humic acid in the washing solution is 0.01 g / L.

[0107] Part of the surface of the cobalt hydroxide obtained in this example is black, and partial oxidation of some products occurs. The SEM image of the obtained cobalt hydroxide is asFigure 7 As shown, from Figure 7 it can be seen that cobalt hydroxide is in a flaky structure, but a large number of products agglomerate.

[0108] Example 8

[0109] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that humic acid is not added to the washing solution.

[0110] The surface of the cobalt hydroxide obtained in this example is black, and the product is severely oxidized. The SEM image of the obtained cobalt hydroxide is as Figure 8 shown, from Figure 8 it can be seen that cobalt hydroxide is in a flaky structure, but a large number of products agglomerate.

[0111] Example 9

[0112] This example provides a method for preparing flaky cobalt hydroxide. The difference compared with Example 1 is only that ammonia water is replaced with a sodium hydroxide solution, and the concentration of the sodium hydroxide solution is the same as the concentration of ammonia water in Example 1.

[0113] The SEM image of the cobalt hydroxide obtained in this example is as Figure 9 shown, from Figure 9 it can be seen that cobalt hydroxide is in a flaky structure, but there is a large amount of product agglomeration and caking.

[0114] Example 10

[0115] This example provides a method for preparing cobalt hydroxide. The difference compared with Example 1 is only that in the precipitation reaction, a solution containing humic acid is not added. After mixing humic acid and a precipitant, the obtained mixed solution is added, and the mixed solution and a cobalt salt solution are added to the reaction bottom liquid;

[0116] The mass of humic acid in the mixed solution is the same as the mass of humic acid in Example 1. Since mixing the precipitant and humic acid will cause the pH value of the precipitant to decrease, it is necessary to increase the amount of the precipitant to keep the pH value of the reaction system the same as that in Example 1.

[0117] The SEM image of the cobalt hydroxide obtained in this example is as Figure 10 shown, from Figure 10 it can be seen that the obtained cobalt hydroxide particles have uneven sizes. This is because in order to maintain the pH value of the reaction system, the addition amount of the precipitant increases, resulting in an increase in the supersaturation of the reaction system. The reaction system is more likely to nucleate, and finally the cobalt hydroxide particles have uneven sizes.

[0118] Comparative Example 1

[0119] This comparative example provides a method for preparing cobalt hydroxide, which is only different from Example 1 in that no humic acid-containing solution is added during the precipitation reaction.

[0120] The SEM image of the cobalt hydroxide obtained in this comparative example is as Figure 11 shown. It can be seen from Figure 11 this that the obtained cobalt hydroxide agglomerates seriously.

[0121] The cobalt hydroxides obtained in Examples 1-10 and Comparative Example 1 were subjected to XRD detection to obtain the characteristic peak intensities of the (001) crystal plane and the (100) crystal plane, which were denoted as I(001) and I(100) respectively. The ratio of I(001) to I(100), i.e., I(001) / I(100), was calculated. The results are shown in Table 1. The ratio of the exposed areas of the (001) plane and the (100) plane of cobalt hydroxide was characterized by I(001) / I(100). The larger the value of I(001) / I(100), the closer the cobalt hydroxide is to the flaky shape, thereby reducing the impedance of the positive electrode material.

[0122] Among Examples 1-10 and Comparative Example 1, there are impurity peaks in the XRD patterns of Examples 4 and 7-8, and the XRD patterns of other examples and comparative examples all show pure phases of cobalt hydroxide. Taking Examples 1-4 and 7-8 as examples, their XRD patterns and the standard PDF card of cobalt hydroxide are as Figure 12 shown. It can be seen from Figure 12 this that there are impurity peaks of cobalt oxyhydroxide in Example 4, and impurity peaks of cobalt oxide in Examples 7-8.

[0123] Table 1

[0124] I(001) / I(100) Example 1 6.11 Example 2 7.21 Example 3 6.53 Example 4 4.23 Example 5 5.26 Example 6 4.76 Example 7 3.42 Example 8 3.86 Example 9 5.14 Example 10 5.32 Comparative Example 1 3.25

[0125] It can be seen from the data in Table 1 that:

[0126] (1) From the data of Examples 1-10, it can be seen that the I(001) / I(100) value of the cobalt hydroxide obtained by the preparation method described in the present disclosure reaches 3.42 or more, and can reach 6.11 or more under better conditions. The flaky structure is excellent, and it can better reduce the impedance of the positive electrode material.

[0127] (2) By comprehensively comparing the data of Example 1, Example 4 and Comparative Example 1, it can be seen that the difference between Example 4 and Example 1 is only that the mass of humic acid accounts for 0.01% of the mass of cobalt element in the cobalt salt solution, and the difference between Comparative Example 1 and Example 1 is only that the humic acid-containing solution is not added in the precipitation reaction. The I(001) / I(100) value in Example 1 reaches 6.11, while Example 4 and Comparative Example 1 can only reach 4.23 and 3.25 respectively. Thus, it can be seen that adding the humic acid-containing solution and controlling the addition amount of humic acid in the precipitation reaction of the present disclosure is beneficial to the formation of flaky cobalt hydroxide.

[0128] (3) By comprehensively comparing the data of Example 1 and Examples 5-6, it can be seen that the pH value of the reaction system in Examples 5-6 is not within the preferred range of the present disclosure compared with Example 1, and the I(001) / I(100) value in Example 1 is significantly higher than that in Examples 5-6. Thus, it can be seen that the present disclosure preferably controls the pH value of the reaction system within a specific range, which is beneficial to further forming a flaky morphology.

[0129] (4) By comprehensively comparing the data of Example 1 and Examples 7-9, it can be seen that the differences between Examples 7-8 and Example 1 are only that the addition amount of humic acid in the washing solution is 0.01 g / L and no humic acid is added to the washing solution respectively, and the difference between Example 9 and Example 1 is only that ammonia water in the washing solution is replaced with sodium hydroxide solution. The I(001) / I(100) value in Example 1 is significantly higher than that in Examples 7-9. Thus, it can be seen that by adding humic acid to the washing solution and controlling the addition amount of humic acid, the dispersion of cobalt hydroxide can be promoted, and by controlling the use of ammonia water or ammonium bicarbonate solution in the washing solution, material caking can be avoided, so that no additional crushing step is required.

[0130] (5) By comprehensively comparing the data of Example 1 and Example 10, it can be seen that the difference between Example 10 and Example 1 is only that after the precipitant and humic acid are mixed, they are then mixed with the cobalt salt solution. The I(001) / I(100) value in Example 1 is significantly higher than that in Example 10, and the sizes of cobalt hydroxide in Example 10 are uneven. Thus, it can be seen that by mixing with the humic acid-containing solution and controlling the mixing method, the morphology of cobalt hydroxide can be further adjusted to be flaky and the sizes are uniform.

[0131] In summary, the preparation method provided by the present disclosure can prepare well-dispersed and non-oxidized flaky cobalt hydroxide, and no additional crushing step is required in the operation process, saving costs and being safe and non-toxic.

Claims

1. A preparation method of flaky cobalt hydroxide, the preparation method comprising the following steps: Mix a precipitant, a cobalt salt solution and humic acid and carry out a precipitation reaction to obtain a slurry; Carry out solid-liquid separation on the slurry, and the separated solid is washed and dried in sequence to obtain flaky cobalt hydroxide; In the mixing, the mass of humic acid accounts for 0.03-0.3% of the mass of cobalt element in the cobalt salt solution; The humic acid serves as a dispersant, an antioxidant and a chelating agent, wherein the humic acid chelates with cobalt ions, promotes the lateral growth of cobalt hydroxide and inhibits the longitudinal growth, thereby obtaining flaky cobalt hydroxide, and the I(001) / I(100) value of the obtained cobalt hydroxide reaches more than 3.

42.

2. The preparation method according to claim 1, wherein In the mixing, the humic acid is added in the form of a humic acid-containing solution.

3. The preparation method according to claim 2, wherein, The mixing method includes: adding a precipitant, a cobalt salt solution and a humic acid-containing solution to the reaction bottom liquid simultaneously.

4. The preparation method according to claim 3, wherein The flow rate of the cobalt salt solution when added is 10-1200 L / h.

5. The preparation method according to claim 1, wherein, A reaction bottom liquid is also added in the mixing.

6. The preparation method according to claim 5, wherein, The reaction bottom liquid is pre-added to the reaction kettle.

7. The preparation method according to claim 6, wherein The volume of the reaction bottom liquid accounts for 30-60% of the volume of the reaction kettle.

8. The preparation method according to claim 5, wherein, The reaction bottom liquid includes a sodium hydroxide solution.

9. The preparation method according to claim 8, wherein The concentration of sodium hydroxide in the reaction bottom liquid is 100-400 g / L.

10. The preparation method according to claim 2, wherein, The solvent of the humic acid-containing solution includes a sodium hydroxide solution.

11. The preparation method according to claim 10, wherein, The concentration of sodium hydroxide in the humic acid-containing solution is 10-40 g / L.

12. The preparation method according to claim 1, wherein, The precipitant includes a sodium hydroxide solution.

13. The preparation method according to claim 12, wherein, The concentration of sodium hydroxide in the precipitant is 100-400 g / L.

14. The preparation method according to claim 1, wherein, The cobalt salt solution contains any one or a combination of at least two of cobalt chloride, cobalt sulfate or cobalt nitrate.

15. The preparation method according to claim 14, wherein, The concentration of cobalt element in the cobalt salt solution is 90-130 g / L.

16. The preparation method according to claim 1, wherein, Stirring is carried out during the precipitation reaction.

17. The preparation method according to claim 16, wherein, The stirring rate is 200-700 r / min.

18. The preparation method according to claim 1, wherein The temperature of the precipitation reaction is 25-50 °C.

19. The preparation method according to claim 1, wherein In the precipitation reaction, the pH value of the reaction system is controlled by the addition amount of the precipitant.

20. The preparation method according to claim 19, wherein, The pH value of the reaction system is 11-13.

21. The preparation method according to claim 1, wherein, Nitrogen is introduced during the precipitation reaction.

22. The preparation method according to claim 21, wherein, The flow rate of the nitrogen is 0.5-30 L / min.

23. The preparation method according to claim 1, wherein The solid-liquid separation method includes filtration.

24. The preparation method according to claim 1, wherein, The washing liquid used for washing includes an ammonium bicarbonate solution or ammonia water.

25. The preparation method according to claim 24, wherein, The concentration of the washing liquid is 5-30 g / L.

26. The preparation method according to claim 24, wherein, Humic acid is also added to the washing liquid.

27. The preparation method according to claim 26, wherein, The concentration of humic acid in the washing liquid is 0.03-0.3 g / L.

28. The preparation method according to claim 1, wherein, The number of washing times ≥ 3 times.

29. The preparation method according to claim 28, wherein The volume of the washing liquid used for each washing is 0.5-1.5 times the volume of the slurry.

30. The preparation method according to claim 1, wherein The preparation method includes the following steps: Using a sodium hydroxide solution with a concentration of 100-400 g / L as the reaction bottom liquid, using a sodium hydroxide solution with a concentration of 100-400 g / L as the precipitant, controlling the concentration of cobalt element in the cobalt salt solution to be 90-130 g / L, the concentration of sodium hydroxide in the humic acid-containing solution to be 10-40 g / L, and the mass of humic acid to account for 0.03-0.3% of the mass of cobalt element in the cobalt salt solution; Pre-add the reaction bottom liquid into the reaction kettle, where the volume of the reaction bottom liquid accounts for 30-60% of the volume of the reaction kettle. Then, add a precipitant, a cobalt salt solution, and a humic acid-containing solution to the reaction bottom liquid. Control the flow rate of the cobalt salt solution during addition to be 10-1200 L / h, and control the addition amount of the precipitant to make the pH value of the reaction system 11-13. Conduct a precipitation reaction under the conditions of a temperature of 25-50 °C, a nitrogen flow rate of 0.5-30 L / min, and a stirring rate of 200-700 r / min to obtain a slurry; Filter the slurry, wash the obtained solid with a washing liquid ≥3 times, and then dry it to obtain flaky cobalt hydroxide; The volume of the washing liquid used for each washing is 0.5-1.5 times the volume of the slurry. The washing liquid includes an ammonium bicarbonate solution or ammonia water. The concentration of the washing liquid is 5-30 g / L, and the concentration of humic acid in the washing liquid is 0.03-0.3 g / L.

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