METHOD OF PREPARING A TERNARY PRECURSOR

Abstract

The present description describes a method for preparing a ternary precursor, which includes the following steps: S1: mixing a first metal salt solution with a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt, ammonia water, and a sodium hydroxide solution, adjusting the pH, and heating and stirring a resulting mixture to allow a reaction; and aging and filtering a resulting suspension to obtain a precursor seed crystal; S2: adding the precursor seed crystal to a dilute acid solution, and stirring and filtering the resulting mixture to obtain an acidified seed crystal; and S3: mixing a second metal salt solution with a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt, a sodium hydroxide solution, and the acidified seed crystal, adjusting the pH, and heating and stirring the resulting mixture to allow a reaction;and aging, filtering, and drying a resulting suspension to obtain the ternary precursor. In the present description, the precursor seed crystal is added to the dilute acid solution, and the resulting mixture is stirred, so that an amorphous micropowder dissolves on the surface of the seed crystal, the crystal structure is more complete, and the primary particles are also thinned under acid leaching conditions, creating favorable conditions for the continuous growth of a crystal plate on the surface of the seed crystal during the subsequent ammonia-free procedure.

Description

Method for preparing ternary precursor TECHNICAL FIELD The present description belongs to the technical field of lithium ion battery (LIB) cathode materials, and specifically refers to a method of preparing a ternary precursor. BACKGROUND With high energy density and cycle performance, ternary LIBs have become the preferred batteries for electric vehicles with long endurance mileage. Ternary precursors are one of the basic materials for preparing ternary LIBs, and thus the performance of ternary precursors plays an important role in the battery's capacity and stability. In recent years, in order to cope with the rapid development of electric vehicles, many ternary precursor manufacturers in China have begun to establish new factories and improve production capacity, leading to increasingly higher performance requirements and increasingly lower cost requirements for ternary precursors. Furthermore, lithium iron phosphate (LFP) batteries have excellent safety performance, causing a substantial impact on the ternary material market and constantly driving advancements in ternary LIBs. Currently, ternary precursors are primarily produced by the coprecipitation method, using NaOH as the precipitating agent and ammonia water as the complexing agent. That is, the materials are continuously pumped into a reactor, and the stirring speed, reaction temperature, pH, ammonia concentration, and solids content are each controlled within a specific range, resulting in a ternary precursor through continuous nucleation and gradual crystal growth to a specified particle size. The presence of ammonia water allows nickel, cobalt, and manganese with different solubility products to complex with ammonia and precipitate homogeneously, thereby obtaining precursor particles with slow growth, uniform composition, coarse primary particles, high sphericity, and high packed density.However, the use of ammonia water inevitably results in a large amount of wastewater containing ammonia nitrogen, which increases the cost of wastewater treatment and the production cost of a precursor. Furthermore, ammonia water is easy to volatilize, causing harm to the environment and human health. In view of this, it is necessary to study the production methods of low-ammonia and ammonia-free precursors. In the related art, a method for preparing a high-performance LIB ternary cathode material at a low ammonia concentration (equal to or less than 0.1 mol / L) does not fundamentally solve the problem of ammonia nitrogen wastewater and increases the production cost due to the introduction of an ammonium salt as a raw material.In the related art, a method is described for preparing a precursor for a multi-element nickel-cobalt-manganese LIB cathode material that does not use ammonia water as a complexing agent. However, the prepared precursor particles are multi-particle agglomerates, which not only have a large number of interfaces but also have a low overall sphericity. Since the reaction begins without ammonia water as a complexing agent, nickel, cobalt, and manganese precipitate rapidly, resulting in inconsistent particle compositions and high surface energy. This results in easy agglomeration to form deformed agglomerated spheres with multiple interfaces and makes it difficult to form complete spherical particles after further growth. Therefore, it is of great value to study a method that uses ammonia water to prepare a seed crystal and then allows the seed crystal to grow in the absence of ammonia, which can not only reduce the cost of wastewater treatment but also produce a precursor with high sphericity and high specific surface area (SSA). However, this method also has some difficulties.For example, because a seed crystal prepared in the presence of ammonia water has coarse primary particles and the primary particles grown in the absence of ammonia are thin, a seed crystal stage and a growth stage cannot be well connected, and renucleation easily occurs to form deformed agglomerated particles, so that the originally added spherical seed crystal does not play an inherent growth-guiding role. SUMMARY The present disclosure aims to address at least one of the technical problems present in the prior art. In view of this, the present disclosure provides a method for preparing a ternary precursor. According to one aspect of the present disclosure, there is provided a method of preparing a ternary precursor, including the following steps: S1: Mixing a first metal salt solution containing a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt with ammonia water and a sodium hydroxide solution, adjusting the pH, carrying out a reaction with heating and stirring to obtain a suspension; aging and filtering the suspension to obtain a precursor seed crystal; S2: Add the precursor seed crystal to a dilute acid solution, stir, and filter the resulting mixture to obtain an acidified seed crystal; and S3: Mixing a second metal salt solution containing a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt with a sodium hydroxide solution and the acidified seed crystal, adjusting the pH, and carrying out a reaction under heating and stirring; and aging, filtering, and drying the resulting suspension to obtain the ternary precursor. In some embodiments of the present invention, in S1, the pH is 10 to 13. In some embodiments of the present invention, in S1, heating is carried out at 40°C to 80°C. In some embodiments of the present invention, in S1, the particles in the suspension have a D50 particle size of 1.5-4 pm. In some embodiments of the present invention, in S2, the dilute acid solution is one or more selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid; and preferably, the dilute acid solution has a concentration of 0.1-1 mol / L. In some embodiments of the present invention, in S2, stirring is carried out for 0.5-2 h. In some embodiments of the present invention, in S3, heating is carried out at 40-80°C. In some embodiments of the present invention, in S3, the pH is 9.0 to 12.0. In some embodiments of the present invention, in S3, the particles in the suspension have a D50 particle size of 3-12 pm. In some embodiments of the present invention, the first metal salt solution and the second metal salt solution may be the same or different. When the two metal salt solutions are the same, the precursor obtained has a uniform composition, and when the two metal salt solutions are different, the precursor obtained is a material with a concentration gradient. In some implementations of the present disclosure, S3 may specifically include: adding the acidified seed crystal and water to the reactor, and starting stirring and heating; introducing an inert gas, and adding the sodium hydroxide solution to the reactor to adjust the pH; and simultaneously pumping the sodium hydroxide solution and the second metal salt solution to allow a reaction, during which the pH of the reaction is constantly adjusted to control nucleation and growth of the precursor particles, a supernatant is filtered into the reactor to maintain a highly stable liquid level, and the particles continuously grow to a target particle size. According to a preferred implementation of the present disclosure, the present disclosure has at least the following beneficial effects: 1. In the present disclosure, ammonia water is used as a complexing agent in the seed crystal preparation step, so that metal ions can be precipitated slowly and uniformly, the phenomenon of multi-particle agglomeration into deformed secondary particles in the absence of ammonia does not easily occur, and the obtained seed crystal has high sphericity and excellent dispersibility. The seed crystal preparation step takes a very short time in the entire reaction procedure, but the amount of seed crystal obtained is sufficient to sustain multiple experiments. 2. In the present disclosure, the precursor seed crystal is added to the dilute acid solution, and the resulting mixture is stirred, so that an amorphous micropowder is dissolved on the surface of the seed crystal, the crystal structure is more complete, and the primary particles are also thinned under acid leaching conditions, which creates favorable conditions for the continuous growth of a crystal plate on the surface of the seed crystal during the subsequent ammonia-free process. 3. In the present disclosure, ammonia water is not used during the subsequent growth stage, and the particles can still continue to grow along the seed crystal morphology and retain a relatively high sphericity, which leads to wastewater containing no ammonia and thereby reduces the cost of wastewater treatment. 4. The ternary precursor prepared by the present disclosure has thin primary particles and large ASE, which helps to improve the reaction activity, contact area with other materials, and uniformity of a cathode material, thus giving a high production capacity. BRIEF DESCRIPTION OF THE DRAWINGS The present description is further described below with reference to the accompanying drawings and examples. FIG. 1 is a scanning electron microscopy (SEM) image of the precursor product obtained in Example 1 of the present disclosure at a magnification of 50,000; FIG. 2 is an SEM image of the precursor product obtained in Example 1 of the present disclosure at a magnification of 1,000; FIG. 3 is an SEM image of the precursor product obtained in Comparative Example 1 of the present disclosure at a magnification of 50,000; and FIG. 4 is an SEM image of the precursor product obtained in Comparative Example 1 of the present disclosure at a magnification of 1,000. DETAILED DESCRIPTION The technical concepts and effects of the present disclosure are clearly and fully described below, along with examples, to enable the objectives, features, and effects of the present disclosure to be fully understood. Apparently, the examples described are merely a few of all the examples in the present disclosure. All other examples obtained by those skilled in the art based on the examples in the present disclosure without creative efforts should be within the scope of protection of the present disclosure. Example 1 In this example, a ternary precursor was prepared, and a specific preparation procedure was as follows: (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water in a ratio of 83:12:5 to prepare a mixed metal salt solution A, and then the mixed metal salt solution A, ammonia water, and sodium hydroxide solution were simultaneously added to a reactor for precipitation; the resulting mixture was stirred to allow a reaction at a pH of 12.0 and a temperature of 60 °C; after a D50 particle size reached 4 pm, the resulting precipitate was aged, filtered, and washed to obtain a precursor seed crystal with high sphericity; the precursor seed crystal was filtered and added to a 1 mol / L dilute hydrochloric acid solution, and the resulting mixture was stirred for 1 h; and an acidified seed crystal was filtered and washed. (2) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in pure water in a ratio of 83:12:5 to prepare a mixed metal salt solution B; an acidified seed crystal and an appropriate amount of pure water were added to a reactor, the resulting mixture was stirred and heated (maintained at 65°C), and nitrogen was continuously introduced into the reactor to prevent oxidation;and a small amount of a sodium hydroxide solution was added to the reactor to adjust the pH in the reactor to 10.0, and then the sodium hydroxide solution and the mixed metal salt solution B were simultaneously pumped into the reactor for co-precipitation, wherein the pH of the reaction was constantly adjusted to control the nucleation and growth of the precursor particles, a supernatant in the reactor was filtered through a microporous filtration device to keep the liquid level in the reactor stable, the solid content in the material in the reactor was continuously increased, and the particles continuously grew to a D50 particle size of 10 pm; (3) Material collection: A material that met the requirements prepared in step (2) was collected in an aging tank, and then filtered, washed, dried, and sieved to obtain a precursor product. FIG. 1 and FIG. 2 are SEM images of the precursor product obtained in Example 1 at magnifications of 50,000 and 1,000, respectively. FIG. 1 shows the surface morphology of a single particle. Since there is no ammonia in the later stage of the reaction, the primary particles grow into small flakes without amorphous micropowder between the flakes, and the secondary particles have high sphericity and show no obvious boundaries on the surface, indicating a complete crystal structure. FIG. 2 shows the overall morphology of a large number of particles, almost all of which are well-developed spherical particles. FIG. 1 and FIG. 2 show that the acidified seed crystal plays an excellent growth-guiding role. Example 2 In this example, a ternary precursor was prepared, and a specific preparation procedure was as follows: (1) Nickel nitrate, cobalt nitrate, and manganese nitrate were dissolved in pure water in a ratio of 92:4:4 to prepare a mixed metal salt solution A, and then the mixed metal salt solution A, ammonia water, and sodium hydroxide solution were simultaneously added to a reactor for precipitation; the resulting mixture was stirred to allow a reaction at a pH of 11.5 and a temperature of 60 °C; after a D50 particle size reached 4 pm, the resulting precipitate was aged, filtered, and washed to obtain a precursor seed crystal with high sphericity; the precursor seed crystal was filtered and added to a 0.8 mol / L dilute sulfuric acid solution, and the resulting mixture was stirred for 1 h; and an acidified seed crystal was filtered and washed. (2) Nickel nitrate, cobalt nitrate and manganese nitrate were dissolved in pure water in a ratio of 82:12:6 to prepare a mixed metal salt solution B; an acidified seed crystal and an appropriate amount of pure water were added to a reactor, the resulting mixture was stirred and heated (maintained at 65°C), and nitrogen was continuously introduced into the reactor to prevent oxidation;and a small amount of a sodium hydroxide solution was added to the reactor to adjust the pH in the reactor to 10.2, and then the sodium hydroxide solution and the mixed metal salt solution B were simultaneously pumped into the reactor for co-precipitation, wherein the pH of the reaction was constantly adjusted to control the nucleation and growth of the precursor particles, a supernatant in the reactor was filtered through a microporous filtration device to keep the liquid level in the reactor stable, the solid content in the material in the reactor was continuously increased, and the particles continuously grew to a D50 particle size of 10 pm; (3) Material collection: A material that met the requirements prepared in step (2) was collected in an aging tank, and then filtered, washed, dried, and sieved to obtain a precursor product. Example 3 In this example, a ternary precursor was prepared, and a specific preparation procedure was as follows: (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water in a ratio of 8:1:1 to prepare a mixed metal salt solution A, and then the mixed metal salt solution A, ammonia water, and sodium hydroxide solution were simultaneously added to a reactor for precipitation; the resulting mixture was stirred to allow a reaction at a pH of 11.8 and a temperature of 65 °C; after a D50 particle size reached 2 pm, the resulting precipitate was aged, filtered, and washed to obtain a precursor seed crystal with high sphericity; the precursor seed crystal was filtered and added to a dilute 0.5 mol / L nitric acid solution, and the resulting mixture was stirred for 1 h; and an acidified seed crystal was filtered and washed. (2) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in pure water in a ratio of 6:2:2 to prepare a mixed metal salt solution B; an acidified seed crystal and an appropriate amount of pure water were added to a reactor, the resulting mixture was stirred and heated (maintained at 65°C), and nitrogen was continuously introduced into the reactor to prevent oxidation;and a small amount of a sodium hydroxide solution was added to the reactor to adjust the pH in the reactor to 10.0, and then the sodium hydroxide solution and the mixed metal salt solution B were simultaneously pumped into the reactor for co-precipitation, wherein the pH of the reaction was constantly adjusted to control the nucleation and growth of the precursor particles, a supernatant in the reactor was filtered through a microporous filtration device to keep the liquid level in the reactor stable, the solid content in the material in the reactor was continuously increased, and the particles continuously grew to a D50 particle size of 5 pm; (3) Material collection: A material that met the requirements prepared in step (2) was collected in an aging tank, and then filtered, washed, dried, and sieved to obtain a precursor product. Example 4 (1) Nickel acetate, cobalt acetate, and manganese acetate were dissolved in pure water in a ratio of 65:15:20 to prepare a mixed metal salt solution A, and then the mixed metal salt solution A, ammonia water, and sodium hydroxide solution were simultaneously added to a reactor for precipitation; the resulting mixture was stirred to allow a reaction at a pH of 12.0 and a temperature of 60 °C; after a D50 particle size reached 1.5 pm, the resulting precipitate was aged, filtered, and washed to obtain a precursor seed crystal with high sphericity; the precursor seed crystal was filtered and added to a dilute 0.4 mol / L hydrochloric acid solution, and the resulting mixture was stirred for 1 h; and an acidified seed crystal was filtered and washed. (2) Nickel acetate, cobalt acetate and manganese acetate were dissolved in pure water in a ratio of 55:12:33 to prepare a mixed metal salt solution B; an acidified seed crystal and an appropriate amount of pure water were added to a reactor, the resulting mixture was stirred and heated (maintained at 55°C), and nitrogen was continuously introduced into the reactor to prevent oxidation;and a small amount of a sodium hydroxide solution was added to the reactor to adjust the pH in the reactor to 10.4, and then the sodium hydroxide solution and the mixed metal salt solution B were simultaneously pumped into the reactor for co-precipitation, wherein the pH of the reaction was constantly adjusted to control the nucleation and growth of the precursor particles, a supernatant in the reactor was filtered through a microporous filtration device to keep the liquid level in the reactor stable, the solid content in the material in the reactor was continuously increased, and the particles continuously grew to a D50 particle size of 3 pm; (3) Material collection: A material that met the requirements prepared in step (2) was collected in an aging tank, and then filtered, washed, dried, and sieved to obtain a precursor product. Example 5 (1) Nickel sulfate, cobalt sulfate, and manganese sulfate were dissolved in pure water in a ratio of 5:2:3 to prepare a mixed metal salt solution A, and then the mixed metal salt solution A, ammonia water, and sodium hydroxide solution were simultaneously added to a reactor for precipitation; the resulting mixture was stirred to allow a reaction at a pH of 11.0 and a temperature of 70 °C; after a D50 particle size reached 1.5 pm, the resulting precipitate was aged, filtered, and washed to obtain a precursor seed crystal with high sphericity; the precursor seed crystal was filtered and added to a 0.3 mol / L dilute sulfuric acid solution, and the resulting mixture was stirred for 1 h; and an acidified seed crystal was filtered and washed.2 (2) Nickel sulfate, cobalt sulfate and manganese sulfate were dissolved in pure water in a ratio of 3:3:3 to prepare a mixed metal salt solution B; an acidified seed crystal and an appropriate amount of pure water were added to a reactor, the resulting mixture was stirred and heated (maintained at 65°C), and nitrogen was continuously introduced into the reactor to prevent oxidation;and a small amount of a sodium hydroxide solution was added to the reactor to adjust the pH in the reactor to 9.8, and then the sodium hydroxide solution and the mixed metal salt solution B were simultaneously pumped into the reactor for co-precipitation, wherein the pH of the reaction was constantly adjusted to control the nucleation and growth of the precursor particles, a supernatant in the reactor was filtered through a microporous filtration device to keep the liquid level in the reactor stable, the solid content in the material in the reactor was continuously increased, and the particles continuously grew to a D50 particle size of 4 pm; (3) Material collection: A material that met the requirements prepared in step (2) was collected in an aging tank, and then filtered, washed, dried, and sieved to obtain a precursor product. Comparative Example 1 In this comparative example, a ternary precursor was prepared. The preparation procedure was different from Example 1 in that the seed crystal obtained in step (1) was directly filtered and washed without acidification. FIG. 3 and FIG. 4 are SEM images of the precursor product obtained in Comparative Example 1 at magnifications of 50,000 and 1,000, respectively. FIG. 1 shows the surface morphology of a single particle. Since there is no ammonia in the later stage of the reaction, the primary particles grow into small flakes with a large amount of amorphous micropowder between the flakes, and the secondary particles have poor sphericity and show an obvious boundary on the surface, indicating different crystal orientations and an incomplete crystal structure. FIG. 4 shows the overall morphology of a large number of particles, and it can be seen that most of the particles are deformed agglomerated secondary particles with a large number of boundaries.It shows that the unacidified seed crystal does not play an excellent growth-guiding role, and new crystal nuclei appear in the subsequent ammonia-free reaction process, some of which voluntarily agglomerate into deformed seed crystals and then continue to grow, and some of which adhere to a surface of the original seed crystal, thus reducing the sphericity and crystallinity of the particles and finally resulting in low sphericity of the final particles. Essay example Table 1 shows the performance data of the precursor products obtained in the examples and the comparative example. Table 1 It can be seen from Table 1 that in Comparative Example 1, since no acidification treatment is carried out, the initial specific discharge capacity at 1 C is 6 mAh / g lower than that in Example 1. The examples in the present description are described in detail with reference to the accompanying drawings, but this description is not limited to the above examples. Within the scope of knowledge possessed by those skilled in the technical field, various changes may also be made without departing from the purpose of this description. Furthermore, the examples in the present description or the features in the examples may be combined with each other in a conflict-free manner.

Claims

1. A method of preparing a ternary precursor, comprising the following steps: S1: mixing a first metal salt solution containing a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt with ammonia water and a sodium hydroxide solution, adjusting the pH, and carrying out a reaction under heating and stirring to obtain a slurry; aging and filtering the slurry to obtain a precursor seed crystal; S2: adding the precursor seed crystal to a dilute acidic solution, and stirring and filtering the resulting mixture to obtain an acidified seed crystal; and S3: mixing a second metal salt solution containing a soluble nickel salt, a soluble cobalt salt, and a soluble manganese salt with a sodium hydroxide solution and the acidified seed crystal, adjusting the pH, and carrying out a reaction under heating and stirring;2. The preparation method according to claim 1, wherein, in S1, the pH is 10-13.

3. The preparation method according to claim 1, wherein, in S1, the heating is carried out at 40-80°C.

4. The preparation method according to claim 1, wherein, in S1, the particles in the suspension have a D50 particle size of 1.5-4 pm.

5. The preparation method according to claim 1, wherein, in S2, the dilute acid solution is one or more selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and perchloric acid;and preferably, the dilute acid solution has a concentration of 0.1-1 mol / L.

6. The preparation method according to claim 1, wherein, in S2, stirring is carried out for 0.5-2 h.

7. The preparation method according to claim 1, wherein, in S3, heating is carried out at 40-80 ° C.

8. The preparation method according to claim 1, wherein, in S3, the pH is 9.0-12.

0.

9. The preparation method according to claim 1, wherein, in S3, the particles in the suspension have a D50 particle size of 3-12 pm.

10. The preparation method according to claim 1, wherein S3 specifically comprises: adding the acidified seed crystal and water to a reactor, and starting stirring and heating; Introduce an inert gas, and add the sodium hydroxide solution to the reactor to adjust the pH; and simultaneously pump the sodium hydroxide solution and the second metal salt solution to carry out the reaction;During the reaction, the pH is constantly adjusted to control the nucleation and growth of the ternary precursor particles, and a supernatant is filtered into the reactor to maintain a highly stable liquid level; the particles continuously grow until they reach a target particle size.

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