Nanoscale cobaltosic oxide as well as preparation method and application thereof

Abstract

The invention provides nanoscale cobaltosic oxide as well as a preparation method and application thereof. The preparation method comprises the following steps: adding a cobalt salt solution and a precipitant solution into a base solution containing a first dispersant in a parallel flow manner, carrying out a co-precipitation reaction, aging slurry after the co-precipitation reaction, and washing the aged material to obtain a washed material; drying the nanoscale cobalt carbonate to obtain nanometer cobalt carbonate; and calcining the nano cobalt carbonate to obtain the nanoscale cobaltosic oxide, wet iron removal treatment is synchronously carried out in the aging process, and a washing solution adopted in the washing process comprises a second dispersing agent. The nanoscale cobaltosic oxide material which is low in magnetic foreign matter content, uniform in particle morphology, small in particle size and good in dispersity is obtained by synergistically matching the wet iron removal process in the aging process under the action of dispersants in different preparation stages; in addition, no protective gas needs to be additionally introduced in the preparation process, and the preparation process is simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery materials, and relates to a nano cobalt tetroxide, a preparation method thereof and uses thereof. Background Art

[0002] Cobalt tetroxide, an oxide of Group VIII belonging to P-type semiconductors, has relatively good empty electron orbits, so electron pairs are relatively easy to fuse with it. Therefore, cobalt tetroxide is a transition metal oxide with excellent performance and can be used as a catalyst. Existing research shows that the particle size and morphology of cobalt tetroxide also have a great influence on its catalytic performance. Nano cobalt tetroxide is expected to obtain better performance than large particle cobalt tetroxide and has important application values in heterogeneous catalysis, cathode materials for lithium-ion batteries, solar absorption materials, pigments, etc.

[0003] The application of nano cobalt tetroxide in cathode materials for lithium-ion batteries is very important. It can be used as a precursor material for lithium cobalt oxide cathode materials; it can also be used as a surface coating for cathode materials, playing a role in reducing residual lithium, forming a LiCoO2 phase on the material surface, and effectively improving the electrochemical performance of the material.

[0004] Existing experiments have shown that lithium cobalt oxide products prepared from cobalt tetroxide with small and uniform particle size, small specific surface area and quasi-spherical shape have better rate performance. Due to the small particle size of small particle lithium cobalt oxide, during the charge and discharge process, lithium ions have shorter ion channels, so it has the characteristics of high rate.

[0005] Lithium cobalt oxide is prepared by high-temperature calcination of cobalt tetroxide and lithium carbonate. The preparation method of small particle lithium cobalt oxide requires cobalt tetroxide to have small particles, and the market demand for nano cobalt tetroxide is becoming more and more obvious.

[0006] CN111717937A discloses a preparation method of nano cobalt tetroxide. This method prepares porous spherical micron-sized cobalt tetroxide particles by hydrothermal method at high temperature. The cobalt tetroxide is composed of many nano-ions, with a fragile structure and easy to break; by ball milling method, the micron-sized cobalt tetroxide is further broken into nano-particles. Strictly controlling conditions such as ball milling solvent, ball diameter and rotation speed can effectively avoid the agglomeration of nano-particles and reduce the average particle diameter of cobalt tetroxide to more than 100 nanometers; this method uses hydrothermal method, which has high requirements for equipment and limited production capacity. CN105271440A discloses a preparation method of nano cobalt tetroxide. This preparation method includes using sol-gel method to first prepare a precursor, and then performing two calcinations at different temperatures to obtain nano cobalt tetroxide powder with regular octahedral morphology. This method uses sol-gel method to prepare nano cobalt tetroxide products, with high cost and low production capacity.

[0007] In addition, the battery materials industry has strict requirements for magnetic foreign matter, and the currently prepared nano-scale cobalt tetroxide has a small particle size, making it extremely difficult to remove iron through dry screening.

[0008] Therefore, how to obtain small-particle nano-scale cobalt tetroxide materials with low magnetic foreign matter content is a technical problem that needs to be solved urgently. Summary of the invention

[0009] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a nano-scale cobalt oxide and its preparation method and use. The preparation method provided by the present invention, through the effect of dispersants in different preparation stages, cooperates with the wet iron removal process in the aging process, to obtain a nano-scale cobalt oxide material with low magnetic foreign matter content, uniform particle morphology, small particle size and good dispersibility; and no additional protective gas is required during the preparation process, which simplifies the preparation process.

[0010] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0011] In a first aspect, the present invention provides a method for preparing nano-scale cobalt tetroxide, the preparation method comprising the following steps:

[0012] Adding the cobalt salt solution and the precipitant solution to the base liquid containing the first dispersant in parallel to perform a coprecipitation reaction, aging the slurry after the coprecipitation reaction, and washing the aged material to obtain a washed material;

[0013] Drying the nano-scale cobalt carbonate to obtain nano-cobalt carbonate;

[0014] calcining the nano-cobalt carbonate to obtain the nano-scale cobalt tetroxide;

[0015] Wherein, wet iron removal is carried out simultaneously during the aging process, and the washing liquid used in the washing process includes a second dispersant.

[0016] In the preparation method of the present invention, a first dispersant is added to the bottom liquid in the coprecipitation reaction stage to obtain nanoscale cobalt carbonate. In the aging stage, wet iron removal is carried out to reduce the content of magnetic foreign matters in the nanoscale cobalt carbonate. Cooperating with the second dispersant in the washing stage can ensure that well-dispersed nanoscale cobalt tetroxide is obtained in the calcination stage without the need for additional crushing treatment after drying, avoiding the introduction of new magnetic foreign matters in the later crushing process and affecting the product quality. Thus, a nanoscale cobalt tetroxide material with low magnetic foreign matter content, uniform particle morphology, small particle size and good dispersibility is obtained. At the same time, in the preparation process of the present invention, there is no need to first prepare nano cobalt hydroxide and then nano cobalt tetroxide. During the preparation of cobalt hydroxide, since cobalt is easily oxidized, a protective gas needs to be introduced additionally, while the present invention does not require the addition of a protective gas, so it also simplifies the preparation process and reduces the cost.

[0017] In the present invention, the first dispersant, wet iron removal and the second dispersant must cooperate synergistically and act together to obtain nanoscale cobalt tetroxide and simultaneously achieve the purpose of reducing the magnetic foreign matters therein.

[0018] In addition, wet iron removal is carried out in the aging stage of the present invention because the efficiency and yield of the ordinary dry screening iron removal method for nanoscale particles are extremely low and cannot meet the production requirements.

[0019] The following are the preferred technical solutions of the present invention, but do not limit the technical solutions provided by the present invention. Through the following preferred technical solutions, the technical objectives and beneficial effects of the present invention can be better achieved.

[0020] Preferably, the cobalt salt includes cobalt sulfate.

[0021] The present invention preferably uses cobalt sulfate as the preparation raw material, and products with the same indexes as cobalt chloride can be made through the adjustment of the preparation process. Compared with the commonly used cobalt chloride system, the sulfate system has less corrosion and lower requirements for the equipment material, which can greatly reduce the equipment investment cost.

[0022] Preferably, the concentration of the cobalt salt solution is 140-180 g / L, such as 140 g / L, 150 g / L, 160 g / L, 170 g / L or 180 g / L, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0023] Preferably, the concentration of the precipitant solution is 180-220 g / L, such as 180 g / L, 190 g / L, 200 g / L, 210 g / L or 220 g / L, etc., but not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0024] Preferably, based on the addition amount of pure water in the bottom liquid being 1 L, the addition amount of the first dispersant in the bottom liquid is 0.5 - 3 g.

[0025] In the present invention, based on the addition amount of pure water in the bottom liquid being 1 L, the addition amount of the first dispersant in the bottom liquid is adjusted to 0.5 - 3 g, which can better avoid particle aggregation and prepare nanoscale particles in the reaction stage. This concentration of dispersant is easier to wash off in the washing stage, reducing the introduction of impurity ions.

[0026] Preferably, the first dispersant includes sodium hexametaphosphate and / or sodium pyrophosphate.

[0027] The type of the first dispersant provided by the present invention is an inorganic dispersant, which is more stable than organic dispersants such as polyethylene glycol or sodium dodecyl sulfate, and can play a role in stable dispersion within a wider pH range.

[0028] Preferably, the bottom liquid further includes a precipitant, and the concentration of the precipitant in the bottom liquid is 100 - 150 g / L, such as 100 g / L, 110 g / L, 120 g / L, 130 g / L, 140 g / L or 150 g / L, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0029] Preferably, the pH value of the coprecipitation reaction is 8 - 8.5, such as 8, 8.1, 8.2, 8.3, 8.4 or 8.5, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0030] Preferably, the reaction temperature of the coprecipitation reaction is 30 - 50 °C, such as 30 °C, 35 °C, 40 °C, 45 °C or 50 °C, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0031] Preferably, the rotation speed of the coprecipitation reaction is 450 - 500 rpm, such as 450 rpm, 460 rpm, 470 rpm, 480 rpm, 490 rpm or 500 rpm, etc., and other unlisted values within this numerical range are equally applicable.

[0032] Preferably, during the coprecipitation reaction, the feeding is stopped after 6 - 10 h of reaction, such as 6 h, 7 h, 8 h, 9 h or 10 h, etc., but is not limited to the listed values, and other unlisted values within this numerical range are equally applicable.

[0033] Preferably, the wet iron removal includes using a wet electromagnetic iron remover to circulate and remove iron for 4 - 10 h, such as 4 h, 5 h, 6 h, 7 h, 8 h, 9 h or 10 h, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0034] In the aging stage of the present invention, iron is removed by circulating for 4 - 10 h, and magnetic foreign matters are removed while removing impurity sulfur.

[0035] Preferably, after the aging is completed, the aged slurry is subjected to cyclic dehydration, and the number of times of cyclic feeding is 2 - 3 times, such as 2 times or 3 times.

[0036] Preferably, the concentration of the second dispersant in the washing liquid is 0.1 - 1 g / L, such as 0.1 g / L, 0.2 g / L, 0.3 g / L, 0.4 g / L, 0.5 g / L, 0.6 g / L, 0.7 g / L, 0.8 g / L, 0.9 g / L or 1 g / L, etc.

[0037] Preferably, the washing temperature in the washing process of the present invention is 50 - 80 °C (such as washing with hot water containing a second dispersant), such as 50 °C, 60 °C, 70 °C or 80 °C, etc., and the number of washing times is 1 - 2 times, such as 1 time or 2 times, etc.

[0038] Preferably, the second dispersant includes any one or a combination of at least two of polyacrylate, polyvinyl acetate or polyvinyl alcohol.

[0039] In the present invention, an organic dispersant is used in the washing stage because the organic matter can be decomposed by high temperature in the calcination stage and has no influence on the impurity content of the product.

[0040] Preferably, the drying method includes flash drying.

[0041] Preferably, the calcination method includes rotary kiln calcination.

[0042] Furthermore, since the crushing process is extremely likely to introduce magnetic foreign matters, and the dry iron removal effect of nano - cobalt ferrite is poor and the yield is extremely low, the present invention preferably adopts the method of flash drying in cooperation with dynamic calcination in a rotary kiln, which plays a role in preventing material caking, eliminates the need for a crushing process, reduces the introduction of magnetic foreign matters, and at the same time ensures that the obtained cobalt ferrite material is nano - sized.

[0043] Preferably, the calcination temperature is 400 - 600 °C, such as 400 °C, 450 °C, 500 °C, 550 °C or 600 °C, etc., but not limited to the listed values, and other unlisted values within this range are equally applicable.

[0044] As a preferred technical solution, the preparation method includes the following steps:

[0045] A cobalt sulfate solution with a concentration of 140 - 180 g / L and a precipitant solution with a concentration of 180 - 220 g / L are fed in parallel into a bottom liquid containing a first dispersant. Based on the addition amount of pure water in the bottom liquid being 1 L, the addition amount of the first dispersant in the bottom liquid is 0.5 - 3 g. The bottom liquid also includes a precipitant with a concentration of 100 - 150 g / L. A coprecipitation reaction is carried out in an environment with a pH value of 8 - 8.5, and the feeding is stopped after 6 - 10 h of reaction.

[0046] The slurry after the coprecipitation reaction is aged, and the aged slurry is subjected to cyclic dehydration with the number of cyclic feeding times being 2 - 3 times to obtain an aged material. The aged material is washed to obtain a washed material.

[0047] The nano - cobalt carbonate is flash - dried to obtain nano - cobalt carbonate.

[0048] The nano - cobalt carbonate is calcined in a rotary kiln at 400 - 600 °C to obtain the nano - cobalt tetroxide.

[0049] Among them, during the aging process, wet iron removal treatment is carried out synchronously. The wet iron removal includes using a wet electromagnetic iron remover to remove iron cyclically for 4 - 10 h. The washing liquid used in the washing process includes a second dispersant, and the concentration of the second dispersant in the washing liquid is 0.1 - 1 g / L.

[0050] It should also be noted that the precipitant in the present invention is a conventional substance, and any conventional precipitant type applicable to the preparation process of cobalt carbonate is applicable in the present invention. For example, the precipitant includes, but is not limited to, ammonium bicarbonate and / or ammonium carbonate.

[0051] In a second aspect, the present invention provides a nano - cobalt tetroxide, which is prepared by the preparation method as described in the first aspect.

[0052] Preferably, the median particle size D50 of the nano - cobalt tetroxide is 100 - 500 nm, such as 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm or 500 nm, etc., but not limited to the listed values. Other unlisted values within this numerical range are equally applicable.

[0053] The nano - cobalt tetroxide material obtained by the present invention has a smaller particle size, and the particle morphology is complete and uniform. A product structure with a median particle size D50 of 100 - 500 nm can be obtained, which broadens its application range and improves its performance when used as a cathode material for batteries.

[0054] In a third aspect, the present invention also provides a use of nano cobalt ferrite, and the use includes using the nano cobalt ferrite as described in the second aspect in the preparation of lithium cobalt oxide cathode materials or the modification of cathode materials.

[0055] It should be noted that the nano cobalt ferrite obtained in the present invention is mainly used as a coating material in the coating process of other cathode materials (such as nickel cobalt manganese lithium oxide cathode materials). It reacts with the residual alkali on the surface of the cathode material, reduces the residual alkali, and forms a lithium cobalt oxide coating layer on the surface, thereby improving the electrochemical performance of the material.

[0056] Compared with the prior art, the present invention has the following beneficial effects:

[0057] In the preparation method of the present invention, a first dispersant is added to the bottom liquid in the coprecipitation reaction stage to obtain nano cobalt carbonate. In the aging stage, wet iron removal is carried out to reduce the content of magnetic foreign matters in the nano cobalt carbonate. In cooperation with the second dispersant in the washing stage, it can ensure that nano cobalt ferrite with good dispersibility is obtained in the calcination stage, without the need for additional crushing treatment after drying, avoiding the introduction of new magnetic foreign matters in the later crushing process and affecting the quality of the product. Thus, a nano cobalt ferrite material with low content of magnetic foreign matters, uniform particle morphology, small particle size and good dispersibility is obtained. At the same time, in the preparation process of the present invention, there is no need to first prepare nano cobalt hydroxide and then nano cobalt ferrite. During the preparation of cobalt hydroxide, due to the easy oxidation of cobalt, a protective gas needs to be additionally introduced, while the present invention does not require the addition of a protective gas, so it also simplifies the preparation process and reduces the cost. Description of the Drawings

[0058] Figure 1 SEM image of cobalt ferrite prepared in Example 1. Detailed Embodiments

[0059] The technical solutions of the present invention 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 invention and should not be regarded as specific limitations on the present invention.

[0060] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in this application are intended to cover non-exclusive inclusion.

[0061] In the description of this application, technical terms such as "first" and "second" are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity, specific order, or primary-secondary relationship of the indicated technical features. In the description of the embodiments of this application, "a plurality of" means more than two, unless otherwise specifically defined.

[0062] Example 1

[0063] This example provides a method for preparing nano cobalt tetroxide, and the preparation method is as follows:

[0064] (1) Prepare cobalt sulfate solution A with a concentration of 150 g / L; prepare precipitant ammonium bicarbonate solution B with a concentration of 200 g / L;

[0065] Bottom liquid preparation: Add 1 cubic meter of pure water to a reactor with a volume of 6 cubic meters, and add ammonium bicarbonate. Adjust the concentration of ammonium bicarbonate in the bottom liquid to 120 g / L, and at the same time add 1 kg of the first dispersant sodium pyrophosphate;

[0066] (2) Add solution A and solution B into the bottom liquid of the reactor in a co-current manner for coprecipitation reaction. The reaction conditions are: reaction temperature 40 °C, reaction pH 8.2, rotation speed 450 rpm, and stop feeding after reacting for 10 h;

[0067] (3) Transfer the materials in the reactor to the aging tank, adjust the concentration of ammonium bicarbonate to 50 g / L, keep the temperature at 40 °C, and circulate for 8 h through a wet electromagnetic separator to obtain an aged slurry;

[0068] (4) Dehydrate the aged slurry through a filter press, circulate the feeding 3 times, and rinse it once with 80 °C hot water (the concentration of polyvinyl alcohol is 0.1 g / L) added with the second dispersant polyvinyl alcohol, and then unload the material to obtain a washed material;

[0069] (5) Dry the washed material at 150 °C using a flash dryer to obtain nano cobalt carbonate;

[0070] (6) Calcinate the nano cobalt carbonate at 400 °C using a rotary kiln, and pass the calcined material through a 100-mesh sieve to finally obtain the finished product of nano cobalt tetroxide.

[0071] Figure 1 The SEM diagram of the cobalt tetroxide prepared in Example 1 is shown. It can be seen from the figure that the cobalt tetroxide sample particles are nano-scale and have good dispersibility.

[0072] Example 2

[0073] This example provides a method for preparing nano cobalt tetroxide, and the preparation method is as follows:

[0074] (1) Prepare a cobalt sulfate solution A with a concentration of 180 g / L; prepare a precipitant ammonium bicarbonate solution B with a concentration of 220 g / L;

[0075] Bottom liquid preparation: Add 1 cubic meter of pure water to a reaction kettle with a volume of 6 cubic meters, and add ammonium bicarbonate to adjust the ammonium bicarbonate concentration of the bottom liquid to 150 g / L. At the same time, add 0.5 kg of the first dispersant sodium pyrophosphate;

[0076] (2) Add solution A and solution B to the bottom liquid of the reaction kettle in a co-current manner for coprecipitation reaction. The reaction conditions are: reaction temperature 50 °C, reaction pH 8.5, rotation speed 500 rpm, and stop feeding after reacting for 6 h;

[0077] (3) Transfer the materials in the reaction kettle to the aging tank, adjust the ammonium bicarbonate concentration to 50 g / L, maintain the temperature at 40 °C, and circulate through a wet electromagnetic iron remover for 4 h to obtain an aged slurry;

[0078] (4) Dehydrate the aged slurry through a filter press, feed it in a cycle 2 times, and wash it 2 times with 50 °C hot water (the concentration of polyvinyl alcohol is 0.5 g / L) added with the second dispersant polyvinyl alcohol, and then unload the material to obtain a washed material;

[0079] (5) Dry the washed material at 150 °C using a flash dryer to obtain nano-scale cobalt carbonate;

[0080] (6) Calcinate the nano-scale cobalt carbonate at 600 °C using a rotary kiln, and pass the calcined material through a 100-mesh sieve to finally obtain a nano-scale cobalt tetroxide finished product.

[0081] Example 3

[0082] This example provides a method for preparing nano-scale cobalt tetroxide, and the preparation method is as follows:

[0083] (1) Prepare a cobalt sulfate solution A with a concentration of 150 g / L; prepare a precipitant ammonium bicarbonate solution B with a concentration of 200 g / L;

[0084] Bottom liquid preparation: Add 1 cubic meter of pure water to a reaction kettle with a volume of 6 cubic meters, and add ammonium bicarbonate to adjust the ammonium bicarbonate concentration of the bottom liquid to 120 g / L. At the same time, add 3 kg of the first dispersant sodium pyrophosphate;

[0085] (2) Add solution A and solution B to the bottom liquid of the reaction kettle in a co-current manner for coprecipitation reaction. The reaction conditions are: reaction temperature 45 °C, reaction pH 8.2, rotation speed 450 rpm, and stop feeding after reacting for 8 h;

[0086] (3) Transfer the materials in the reaction kettle to the aging tank, adjust the ammonium bicarbonate concentration to 50 g / L, maintain the temperature at 40 °C, and circulate through a wet electromagnetic iron remover for 8 h to obtain an aged slurry;

[0087] (4) Dehydrate the aged slurry through a filter press, feed it cyclically 3 times, and rinse it once with 60°C hot water (the concentration of polyvinyl alcohol is 1 g / L) added with a second dispersant polyvinyl alcohol, then unload to obtain the washed material;

[0088] (5) Dry the washed material at 150°C using a flash dryer to obtain nanoscale cobalt carbonate;

[0089] (6) Calcinate the nanoscale cobalt carbonate in a rotary kiln at 500°C, sieve the calcined material through a 100-mesh sieve, and finally obtain the finished product of nanoscale cobalt tetroxide.

[0090] Example 4

[0091] The difference between this example and Example 1 is that the first dispersant in step (1) of this example is sodium hexametaphosphate, and the second dispersant in step (4) is polyvinyl acetate.

[0092] The remaining preparation methods and parameters are the same as those in Example 1.

[0093] Example 5

[0094] The difference between this example and Example 1 is that the cobalt salt in step (1) of this example is cobalt chloride instead of cobalt sulfate.

[0095] The remaining preparation methods and parameters are the same as those in Example 1.

[0096] Example 6

[0097] The difference between this example and Example 1 is that the addition amount of the first dispersant sodium pyrophosphate in step (1) of this example is 0.3 kg.

[0098] The remaining preparation methods and parameters are the same as those in Example 1.

[0099] Example 7

[0100] The difference between this example and Example 1 is that the addition amount of the first dispersant sodium pyrophosphate in step (1) of this example is 3.3 kg.

[0101] The remaining preparation methods and parameters are the same as those in Example 1.

[0102] Example 8

[0103] The difference between this example and Example 1 is that the first dispersant in step (1) of this example is polyethylene glycol.

[0104] The remaining preparation methods and parameters are the same as those in Example 1.

[0105] Example 9

[0106] The difference between this example and Example 1 is that in step (4) of this example, the concentration of the second dispersant is 0.05 g / L.

[0107] The remaining preparation methods and parameters are the same as those in Example 1.

[0108] Example 10

[0109] The difference between this example and Example 1 is that in step (4) of this example, the concentration of the second dispersant is 1.5 g / L.

[0110] The remaining preparation methods and parameters are the same as those in Example 1.

[0111] Example 11

[0112] The difference between this example and Example 1 is that in step (4) of this example, the second dispersant is polyvinyl alcohol.

[0113] The remaining preparation methods and parameters are the same as those in Example 1.

[0114] Example 12

[0115] The difference between this example and Example 1 is that in step (5) of this example, the drying method is drying in a common oven.

[0116] The remaining preparation methods and parameters are the same as those in Example 1.

[0117] Example 13

[0118] The difference between this example and Example 1 is that in step (6) of this example, the calcination method is calcination in a muffle furnace.

[0119] The remaining preparation methods and parameters are the same as those in Example 1.

[0120] Comparative Example 1

[0121] The difference between this comparative example and Example 1 is that in the bottom liquid of step (1) of this example, the first dispersant is not added.

[0122] The remaining preparation methods and parameters are the same as those in Example 1.

[0123] Comparative Example 2

[0124] The difference between this comparative example and Example 1 is that in the aging process of step (3) of this comparative example, wet iron removal is not carried out.

[0125] The remaining preparation methods and parameters are the same as those in Example 1.

[0126] Comparative Example 3

[0127] The difference between this comparative example and Example 1 is that in step (4) of this comparative example, no second dispersant is added.

[0128] The remaining preparation methods and parameters are the same as those in Example 1.

[0129] The Co₃O₄ finished products obtained from Examples 1 - 13 and Comparative Examples 1 - 3 were tested for particle size and the content of magnetic foreign substances.

[0130] Particle size test: A laser particle size analyzer was used to test the particle size.

[0131] Test for the content of magnetic foreign substances: The ICP test method was used.

[0132] The test results of the above tests are shown in Table 1.

[0133] Table 1

[0134]

[0135]

[0136] Note: PPb in the table is one part per billion.

[0137] In summary, in the preparation method of the present invention, a first dispersant is added to the bottom liquid in the coprecipitation reaction stage to obtain nano - sized cobalt carbonate. Wet - process iron removal is carried out in the aging stage to reduce the content of magnetic foreign substances in the nano - sized cobalt carbonate. Cooperating with the second dispersant in the washing stage can ensure that well - dispersed nano - sized Co₃O₄ is obtained in the calcination stage, without the need for additional crushing treatment after drying, avoiding the introduction of new magnetic foreign substances in the later crushing process and affecting the product quality; thus, a nano - sized Co₃O₄ material with a low content of magnetic foreign substances, uniform particle morphology, small particle size and good dispersion is obtained. At the same time, in the preparation process of the present invention, there is no need to first prepare nano - cobalt hydroxide and then nano - Co₃O₄. During the preparation of cobalt hydroxide, since cobalt is easily oxidized, additional protective gas is introduced, while the present invention does not require the addition of protective gas, so it also simplifies the preparation process and reduces costs.

[0138] The applicant declares that the above - mentioned is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of nano cobalt tetroxide, characterized in that, The preparation method comprises the following steps: A cobalt salt solution and a precipitant solution are added in parallel into a bottom liquid containing a first dispersant for coprecipitation reaction. The slurry after the coprecipitation reaction is aged, and the aged material is washed to obtain a washed material; The nano cobalt carbonate is dried to obtain nano cobalt carbonate; The nano cobalt carbonate is calcined to obtain the nano cobalt tetroxide; Wherein, during the aging process, wet iron removal treatment is synchronously carried out, and the washing liquid used in the washing process includes a second dispersant.

2. The preparation method according to claim 1, wherein The cobalt salt includes cobalt sulfate; Preferably, the concentration of the cobalt salt solution is 140 - 180 g / L; Preferably, the concentration of the precipitant solution is 180 - 220 g / L; Preferably, based on the addition amount of pure water in the bottom liquid being 1 L, the addition amount of the first dispersant in the bottom liquid is 0.5 - 3 g; Preferably, the first dispersant includes sodium hexametaphosphate and / or sodium pyrophosphate; Preferably, the bottom liquid further includes a precipitant, and the concentration of the precipitant in the bottom liquid is 100 - 150 g / L.

3. The preparation method according to claim 1, characterized in that, The pH value of the coprecipitation reaction is 8 - 8.5, the reaction temperature of the coprecipitation reaction is 30 - 50 °C, the rotation speed of the coprecipitation reaction is 450 - 500 rpm, and during the coprecipitation reaction, the feeding is stopped after reacting for 6 - 10 h.

4. The preparation method according to claim 1 or 2, characterized in that, The wet iron removal includes using a wet electromagnetic iron remover for cyclic iron removal for 4 - 10 h; Preferably, after aging, the aged slurry is subjected to cyclic dehydration, and the number of times of cyclic feeding is 2 - 3 times.

5. The preparation method according to claim 1 or 2, characterized in that, The concentration of the second dispersant in the washing liquid is 0.1 - 1 g / L; Preferably, the second dispersant includes any one or a combination of at least two of polyacrylate, polyvinyl acetate or polyvinyl alcohol; 6. The preparation method according to claim 1, characterized in that, The drying method includes flash drying; Preferably, the calcination method includes rotary kiln calcination; Preferably, the calcination temperature is 400 - 600 °C.

7. The preparation method according to claim 1, characterized in that, The preparation method comprises the following steps: A cobalt sulfate solution with a concentration of 140 - 180 g / L and a precipitant solution with a concentration of 180 - 220 g / L are added in parallel into a bottom liquid containing a first dispersant. Based on the addition amount of pure water in the bottom liquid being 1 L, the addition amount of the first dispersant in the bottom liquid is 0.5 - 3 g, and the bottom liquid further includes a precipitant with a concentration of 100 - 150 g / L. The coprecipitation reaction is carried out in an environment with a pH value of 8 - 8.5, and the feeding is stopped after reacting for 6 - 10 h; The slurry after the coprecipitation reaction is aged, the aged slurry is subjected to cyclic dehydration, and the number of times of cyclic feeding is 2 - 3 times to obtain an aged material. The aged material is washed to obtain a washed material; The nano cobalt carbonate is flash dried to obtain nano cobalt carbonate; The nano cobalt carbonate is calcined in a rotary kiln at 400 - 600 °C to obtain the nano cobalt tetroxide; Among them, during the aging process, wet iron removal treatment is carried out synchronously. The wet iron removal includes using a wet electromagnetic iron remover to circulate and remove iron for 4 to 10 hours; the washing liquid used during the washing process includes a second dispersant, and the concentration of the second dispersant in the washing liquid is 0.1 to 1 g / L.

8. A nanoscale cobalt ferrite, characterized in that, The nano cobalt ferrite is prepared by the preparation method according to any one of claims 1-7.

9. The nano cobalt ferrite according to claim 8, characterized in that, The median particle size D50 of the nano cobalt ferrite is 100 to 500 nm.

10. Use of nano cobalt ferrite, characterized in that, The uses include using the nano cobalt ferrite according to claim 8 or 9 in the preparation of lithium cobalt oxide cathode materials or the modification of cathode materials.

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