阅读说明：本技术 一种镍钴铝三元前驱体及其制备方法 (Nickel-cobalt-aluminum ternary precursor and preparation method thereof ) 是由 侯鑫宇 孟立君 刘宙 张海艳 胡志兵 黎力 苗小欢 于 2021-11-22 设计创作，主要内容包括：本发明属于锂离子电池材料技术领域,具体涉及一种镍钴铝三元前驱体及其制备方法。本发明通过控制反应溶液的流量,在反应的第一阶段维持反应体系的碱度恒定,在反应的第二阶段维持反应体系的pH值和碱度恒定,制备得到粒度分布集中、结晶型好的前驱体。本发明在制备前驱体的过程中不需要气氛保护,核量控制方法简单,成核过程不需要人为介入调整pH值,前驱体生成一致性好,可实现批量化生产,具有广泛应用前景。(The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a nickel-cobalt-aluminum ternary precursor and a preparation method thereof. The method maintains the alkalinity of the reaction system to be constant in the first stage of the reaction and maintains the pH value and the alkalinity of the reaction system to be constant in the second stage of the reaction by controlling the flow of the reaction solution, so as to prepare the precursor with concentrated particle size distribution and good crystallization. The method does not need atmosphere protection in the process of preparing the precursor, has simple control method of the nucleation, does not need artificial intervention to adjust the pH value in the nucleation process, has good consistency of precursor generation, can realize batch production, and has wide application prospect.)

1. The preparation method of the nickel-cobalt-aluminum precursor is characterized by comprising the following steps of:

step S1: according to the formula Ni_xCo_yAl_1-x-y(OH)₂Preparing mixed salt solution of nickel and cobalt, wherein x is more than or equal to 0.8<1，0.05≤y<0.2; dissolving and diluting aluminum sulfate solid by using a sodium hydroxide solution to obtain an alkali aluminum solution; preparing an alkali solution and an ammonia solution;

step S2: preparing a reaction kettle bottom solution;

step S3: introducing a mixed salt solution of nickel and cobalt, an alkali aluminum solution, an alkali solution and an ammonia water solution into a bottom solution of the reaction kettle to carry out coprecipitation reaction, wherein the reaction is divided into two stages: in the first stage, the flow rates of a mixed salt solution of nickel and cobalt, an alkali aluminum solution and an alkali solution are fixed, and the flow rate of ammonia water is adjusted to maintain the alkalinity constant; in the second stage, the flow rates of the mixed salt solution of nickel and cobalt and the alkali-aluminum solution are fixed, and the flow rates of the alkali solution and the ammonia solution are adjusted to maintain the pH value and the alkalinity constant; the reaction time of the first stage accounts for 0.5-5% of the total reaction time;

step S4: and after the reaction is finished, filtering, washing, drying and screening the slurry obtained by the reaction to obtain the nickel-cobalt-aluminum ternary precursor.

2. The preparation method according to claim 1, wherein the molar concentration of total metal ions in the mixed salt solution of nickel and cobalt is 0.5 to 2.5mol/L, the concentration of aluminum in the alkali aluminum solution is 0.1 to 1.5mol/L, the concentration of alkali in the alkali aluminum solution is 1 to 5mol/L, the concentration of the alkali solution is 1 to 10mol/L, and the concentration of the aqueous ammonia solution is 2 to 6 mol/L.

3. The preparation method of claim 1, wherein the bottom solution of the reaction kettle consists of pure water, an alkali solution and an ammonia water solution, and the alkalinity is 10-40 g/L.

4. The method of claim 3, wherein the temperature of the bottom solution of the reaction vessel is 45 to 70 ℃.

5. The method according to claim 1, wherein in the first stage of step S3, the flow rates of the mixed salt solution of nickel and cobalt, the alkali solution and the alkali aluminum solution are as follows: the alkali solution flow rate × alkali concentration in the alkali solution + alkali aluminum solution flow rate × alkali concentration in the alkali aluminum solution = the flow rate of the mixed salt solution of nickel and cobalt × 0.4.

6. The method of claim 5, wherein in the second stage of step S3, the flow rates of the mixed salt solution of Ni and Co and the alkali-Al solution are the same as in the first stage.

7. The method of claim 1, wherein the alkalinity of the first and second stages of step S3 is 15-35g/L, and the pH of the second stage is 11.80-12.30.

8. The process according to claim 1, wherein the total reaction time is 40 to 70 hours.

9. The nickel-cobalt-aluminum precursor is characterized in that the chemical formula of the precursor is Ni_xCo_yAl_1-x-y(OH)₂Wherein x is more than or equal to 0.8<1，0.05≤y<0.2, the median particle size of the precursor is 2-5 μm, the particle size distribution is concentrated, the radial distance ((D90-D10)/D50) is less than or equal to 0.90, and the tap density is more than 1.6g/cm³The specific surface area is 6-14m²And/g, the secondary particles are formed into spheroids by agglomeration of a plurality of primary particles, the primary particles are rectangular in plan view, the length of the primary particles is 200-1000 nm, and the thickness of the primary particles is 100-400 nm.

Technical Field

The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a preparation method of a nickel-cobalt-aluminum ternary precursor.

Background

The lithium ion battery cathode material with low cobalt and high nickel is favored due to its high capacity and low price, and a representative nickel-cobalt lithium aluminate (NCA) material has been widely applied in the field of new energy vehicles, but in terms of the preparation process, the nickel-cobalt-aluminum cathode material has a higher technical threshold, and also faces a larger technical problem as an essential raw material nickel-cobalt-aluminum precursor in the nickel-cobalt lithium aluminate material. If Ni and Co and Al elements have large difference in precipitation pH value, the performance on the order of solubility product constant is very obvious, Ni (OH)₂Has a solubility product constant of the order of 10^-16，Co(OH)₂Has a solubility product constant of the order of 10^-14.9，Al（OH）₃Has a solubility product constant of the order of 10^-33. Meanwhile, ammonia water can not be complexed with aluminum, which causes the phenomenon of uneven precipitation of Ni, Co and Al in the conventional coprecipitation, and because of Al (OH)₃The rapid precipitation of (2) can form new crystal nucleus, delay the growth of crystal and broaden the particle size distribution. In addition, since Al (OH)₃The amphoteric property of the acid and the alkali ensures that the alkali and the alkali can react with NaOH solution to decompose and form AlO under the condition of higher pH₂ ^-Resulting in loss of Al element and formation of flocculent products at lower pH values, resulting in non-idealA single layered structure of states. These problems not only lead to complex process control and poor consistency of precursor products in the precursor preparation process, but also further lead to sudden drop of specific capacity, cycle performance and the like of the nickel-cobalt lithium aluminate material obtained by calcining the precursor.

In the conventional discontinuous production process, the synthesis section is mainly divided into two stages: precursor nucleation and precursor growth. The transition between the two phases is achieved by nucleation at high pH, growth at lower pH. The nucleation quantity is controlled by the nucleation pH value and the maintaining time of the pH value, the adjusting rate of the pH down-regulation stage can directly cause agglomeration of materials in different degrees, and under the existing production condition, the pH down-regulation rate is difficult to control, on one hand, the feedback of pH change is too sensitive, small deviation can cause larger pH value fluctuation, on the other hand, the pH meter commonly used in the market has test errors in the using process, and the fluctuation of the pH in the error range can also directly influence the agglomeration degree. The controllability of the agglomeration degree is poor, the deviation of the synthesis period can be caused, the consistency of the precursor is seriously influenced, great difficulty is brought to stable mass production, and meanwhile, the difference of the precursor indexes can also cause more negative influences on the preparation of the subsequent anode material.

Disclosure of Invention

Aiming at the defects of the prior art, the invention provides a preparation method of a nickel-cobalt-aluminum precursor, which does not need human intervention to adjust the pH value.

In order to achieve the purpose, the invention adopts the following technical scheme.

A preparation method of a nickel-cobalt-aluminum precursor comprises the following steps:

step S1: according to the formula Ni_xCo_yAl_1-x-y(OH)₂Preparing mixed salt solution of nickel and cobalt, wherein x is more than or equal to 0.8<1，0.05≤y<0.2; dissolving and diluting aluminum sulfate solid by using 10mol/L sodium hydroxide solution to obtain alkali aluminum solution; preparing an alkali solution and an ammonia solution;

step S2: preparing a reaction kettle bottom solution;

step S3: introducing a mixed salt solution of nickel and cobalt, an alkali aluminum solution, an alkali solution and an ammonia water solution into a bottom solution of the reaction kettle to carry out coprecipitation reaction, wherein the reaction is divided into two stages: in the first stage, the flow rates of a mixed salt solution of nickel and cobalt, an alkali aluminum solution and an alkali solution are fixed, and the flow rate of ammonia water is adjusted to maintain the alkalinity constant; in the second stage, the flow rates of the mixed salt solution of nickel and cobalt and the alkali-aluminum solution are fixed, and the flow rates of the alkali solution and the ammonia solution are adjusted to maintain the pH value and the alkalinity constant; the reaction time of the first stage accounts for 0.5-5% of the total reaction time;

step S4: and after the reaction is finished, filtering, washing, drying and screening the slurry obtained by the reaction to obtain the nickel-cobalt-aluminum ternary precursor.

In the actual production process, the ammonia water concentration of the slurry is generally measured by an acid-base titration method; as the reaction system is alkaline, the alkalinity in the synthesis process is the mixed concentration of the ammonia water and the alkali in the system.

In the coprecipitation reaction, the pH value in the reaction process influences the nucleation and growth of crystal particles, when the pH value is lower, the supersaturation degree in a solution system is small, and the growth speed of precursor particles is higher than the nucleation speed; when the pH value is higher, the supersaturation degree in the solution system is large, the nucleation speed of crystal nucleus is dominant, and the ammonia water can effectively complex the metal ions newly added into the system, so that the interference of newly added raw materials in the system on the balance of precipitation is relieved, and meanwhile, the supersaturation degree of precipitates in the solution is controlled, and the crystals can slowly grow.

It should be noted that when the mixed salt solution of nickel and cobalt, the alkali aluminum solution, the alkali solution and the ammonia solution are just introduced into the bottom solution of the reaction kettle, a large amount of nuclei are formed in the reaction system due to supersaturation of the solution, and the alkali solution in the system is greatly consumed, so that the alkalinity is reduced. The increase of the ammonia concentration will slow down the nucleation speed of the crystal nucleus, so that the crystal is biased to grow. As the pH drops due to the consumption of the alkali solution and the concentration of the ammonia solution is further increased, the nucleation of the reaction system is converted from the first stage to the growth of the second stage.

It should be noted that in the pH range of 7 to 14, the precipitation rate of Al gradually slows down with increasing pH and even Al (O) occursH）₃Dissolving. When the pH is higher, the precipitation rate of Al is relatively slower, and at the moment, nickel and cobalt are biased to form nuclei due to overlarge system saturation, so that in the invention, nickel ions and cobalt ions are complexed by higher ammonia water concentration to slow down the nucleation rate, so that the Ni ions, the Co ions and the Al ions are uniformly precipitated.

Further, the molar concentration of total metal ions in the mixed salt solution of nickel and cobalt is 0.5-2.5 mol/L, the concentration of aluminum in the alkali aluminum solution is 0.1-1.5mol/L, the concentration of alkali in the alkali aluminum solution is 1-5mol/L, the concentration of the alkali solution is 1-10mol/L, and the concentration of the ammonia water solution is 2-6 mol/L.

Further, the bottom liquid of the reaction kettle consists of pure water, an alkali solution and an ammonia water solution, and the alkalinity is 10-40 g/L.

Further, the temperature of the reaction base solution was 45 to 70 ℃.

Further, in the first stage of step S3, the flow rates of the mixed salt solution of nickel and cobalt, the alkali solution, and the alkali aluminum solution are required to satisfy: the alkali solution flow rate × alkali concentration in the alkali solution + alkali aluminum solution flow rate × alkali concentration in the alkali aluminum solution = the flow rate of the mixed salt solution of nickel and cobalt × 0.4.

Further, in the second stage of step S3, the flow rates of the mixed salt solution of nickel and cobalt and the alkali aluminum solution are the same as those in the first stage.

Further, the alkalinity in the step S3 is 15-35g/L, and the pH value is 11.80-12.30.

Further, the total reaction time is 40-70 h.

Based on the same inventive concept, the invention also provides a nickel-cobalt-aluminum precursor prepared by the method, wherein the chemical formula of the precursor is Ni_xCo_yAl_1-x-y(OH)₂Wherein x is more than or equal to 0.8<1，0.05≤y<0.2, the median particle size of the precursor is 2-5 μm, the particle size distribution is concentrated, the radial distance ((D90-D10)/D50) is less than or equal to 0.90, and the tap density is more than 1.6g/cm³The specific surface area is 6-14m²The secondary particles are formed into spheroids by the agglomeration of a plurality of primary particles, the primary particles are rectangular in plan view, the length of the primary particles is 200-1000 nm, and the thickness of the primary particles is 100-100%400nm。

Compared with the prior art, the invention has the following beneficial effects:

(1) the nickel-cobalt-aluminum precursor provided by the invention has the advantages of concentrated particle size distribution and good crystallization;

(2) the method does not need atmosphere protection in the process of preparing the precursor, has simple control method of the nucleation, does not need artificial intervention to adjust the pH value in the nucleation process, has good consistency of precursor generation, can realize batch production, and has wide application prospect.

Drawings

Fig. 1 is a scanning electron microscope image of a nickel-cobalt-aluminum precursor prepared in example 1 of the present invention.

Fig. 2 is a scanning electron microscope image of the nickel-cobalt-aluminum precursor prepared in example 2 of the present invention.

Fig. 3 is a scanning electron microscope image of the nickel-cobalt-aluminum precursor prepared in example 3 of the present invention.

Detailed Description

In order to make the objects, technical solutions and advantageous effects of the present invention more clearly apparent, the present invention will be described in further detail with reference to the accompanying drawings and the detailed description. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.

Example 1

Preparing a nickel-cobalt-aluminum precursor, comprising the following steps:

(1) according to the formula Ni_0.93Co_0.05Al_0.02(OH)₂Preparing a mixed salt solution with the total concentration of nickel and cobalt of 2mol/L according to the proportion of the medium metal ions; preparing 4mol/L sodium hydroxide solution; preparing 6mol/L ammonia water solution; an alkaline aluminum solution containing 4mol/L sodium hydroxide and 0.3mol/L aluminum salt was prepared.

(2) Adding pure water into a 300L reaction kettle, controlling the temperature to be 65 ℃, adding an ammonia water solution to adjust the alkalinity to be 25g/L, and adding a sodium hydroxide solution to adjust the alkalinity to be 30 g/L. And (2) adding the solution prepared in the step (1) into a reaction kettle to perform coprecipitation reaction. In the first stage of the coprecipitation reaction, the flow rates of the mixed salt solution, the sodium hydroxide solution and the alkali aluminum solution are controlled by adjusting the flow rate of ammonia water to maintain the alkalinity of a reaction system to be 30 +/-0.5 g/L, wherein the flow rates of the mixed salt solution, the sodium hydroxide solution and the alkali aluminum solution are in a relation of the flow rate of the sodium hydroxide solution, the alkali concentration of the sodium hydroxide solution, the flow rate of the alkali aluminum solution, the alkali concentration of the alkali aluminum solution, and the mixed salt solution flow rate is multiplied by 0.4. After 2.5h of reaction, the second stage is started, the pH value of the system is measured to be 12.17, the flow of the sodium hydroxide solution is adjusted to control the pH value of the reaction system to be 12.17 +/-0.05, the flow of the ammonia water is adjusted to maintain the alkalinity to be 30 +/-0.5 g/L, the temperature in the whole reaction process is controlled to be 65 ℃, and the reaction is stopped after 58 h.

(3) Filtering, washing, drying and screening the slurry obtained by the reaction to obtain Ni_0.93Co_0.05Al_0.02(OH)₂Nickel cobalt aluminum ternary precursor.

FIG. 1 is a scanning electron microscope image of a precursor, from which it can be seen that secondary particles of the precursor are agglomerated by a plurality of primary particles to form a spheroid, the primary particles are square rectangles in a plan view, the length of the primary particles is 300-600 nm, and the thickness of the primary particles is 150-300 nm.

Further analysis of other physical indexes of the precursor gave D50 of 2.924 μm, a radial distance of 0.799, and a tap density of 1.86g/cm³The specific surface area is 10.42m²/g。

Example 2

Preparing a nickel-cobalt-aluminum precursor, comprising the following steps:

(1) according to the formula Ni_0.93Co_0.05Al_0.02(OH)₂Preparing a mixed salt solution of nickel and cobalt with the total metal ion concentration of nickel and cobalt being 2mol/L according to the proportion of the medium metal ions; preparing 4mol/L sodium hydroxide solution; preparing 6mol/L ammonia water solution; an alkaline aluminum solution containing 4mol/L sodium hydroxide and 0.3mol/L aluminum salt was prepared.

(2) Adding pure water into a 300L reaction kettle, controlling the temperature to be 65 ℃, adding an ammonia water solution to adjust the alkalinity to be 15g/L, and adding a sodium hydroxide solution to adjust the alkalinity to be 20 g/L. And (2) adding the solution prepared in the step (1) into a reaction kettle to perform coprecipitation reaction. In the first stage of the coprecipitation reaction, the flow rates of the mixed salt solution, the sodium hydroxide solution and the alkali aluminum solution are maintained to be a fixed flow rate reaction according to the relation of the flow rate of the sodium hydroxide solution multiplied by the alkali concentration in the sodium hydroxide solution + the flow rate of the alkali aluminum solution multiplied by the alkali concentration in the alkali aluminum solution = the flow rate of the mixed salt solution multiplied by 0.4, the flow rate of ammonia water is adjusted to maintain the alkalinity to be 30 +/-0.5 g/L, the second stage is started after the reaction is carried out for 1.5h, the pH value of the reaction system is measured to be 11.94 at the moment, the pH value is controlled to be 11.94 +/-0.05 by adjusting the flow rate of the sodium hydroxide, the flow rate of the ammonia water is adjusted to maintain the alkalinity to be 30 +/-0.5 g/L, the temperature in the whole reaction process is controlled to be 65 ℃, and the reaction is stopped after 49 h.

(3) Filtering, washing, drying and screening the slurry obtained by the reaction to obtain Ni_0.93Co_0.05Al_0.02(OH)₂Nickel cobalt aluminum ternary precursor.

FIG. 2 is a scanning electron microscope image of the precursor, from which it can be seen that the secondary particles are agglomerated by a plurality of primary particles to form a spheroid, the primary particles are square rectangles in a plan view, the length of the primary particles is 200-500 nm, and the thickness of the primary particles is 100-200 nm.

Further analysis of other physical indexes of the precursor gave a D50 value of 3.115. mu.m, a radial distance of 0.872, and a tap density of 2.01g/cm³Specific surface area of 11.59m²/g。

Example 3

Preparing a nickel-cobalt-aluminum precursor, comprising the following steps:

(1) according to the formula Ni_0.95Co_0.04Al_0.01(OH)₂Preparing a mixed salt solution of nickel and cobalt with the total metal ion concentration of nickel and cobalt being 2 mol/L; preparing 4mol/L sodium hydroxide solution; preparing 6mol/L ammonia water solution; an alkaline aluminum solution containing 4mol/L sodium hydroxide and 0.3mol/L aluminum salt was prepared.

(2) Adding pure water into a 300L reaction kettle, controlling the temperature at 60 ℃, adding an ammonia water solution to adjust the alkalinity to 20g/L, and adding a sodium hydroxide solution to adjust the alkalinity to 23 g/L. And (2) adding the solution prepared in the step (1) into a reaction kettle to perform coprecipitation reaction. In the first stage of coprecipitation reaction, the flow of mixed salt solution, sodium hydroxide solution and alkali aluminum solution maintains fixed flow reaction according to the relation of the flow of sodium hydroxide solution multiplied by the alkali concentration in the sodium hydroxide solution + the flow of alkali aluminum solution multiplied by the alkali concentration in the alkali aluminum solution = the flow of mixed salt solution multiplied by 0.4, the flow of ammonia water is adjusted to maintain alkalinity at 23 +/-0.5 g/L, after 2.0h of reaction, the second stage is started, the pH value of the system is measured to be 12.06 at the moment, the flow of sodium hydroxide solution is adjusted to control the pH at 12.06 +/-0.05, the flow of ammonia water is adjusted to maintain alkalinity at 30 +/-0.5 g/L, the temperature in the whole reaction process is controlled to be 60 ℃, and the reaction is stopped after 67 h.

(3) Filtering, washing, drying and screening the slurry obtained by the reaction to obtain Ni_0.95Co_0.04Al_0.01(OH)₂Nickel cobalt aluminum ternary precursor.

FIG. 3 is a scanning electron microscope image of the precursor, from which it can be seen that the secondary particles are agglomerated by a plurality of primary particles to form a spheroid, the primary particles are square rectangles in a plan view, the length of the primary particles is 300-800 nm, and the thickness of the primary particles is 110-250 nm.

Further analysis of other physical indexes of the precursor gave a D50 value of 2.657 μm, a caliper of 0.852, and a tap density of 1.91g/cm³Specific surface area of 7.88m²/g。

The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.