A method for preparing an aluminum-coated precursor

Abstract

The application belongs to the field of lithium ion battery materials, and particularly relates to a preparation method of an aluminum-coated precursor. x Co y Mn z (OH)2, x+y+z=1, and 0<=x<=1, 0<=y<=1, 0<=z<=1; an aluminum sulfate solution with a certain concentration and pH is configured; the aluminum sulfate solution is added into a reaction kettle, and an appropriate adding speed, temperature and stirring speed are controlled; after the addition is completed, a certain amount of sodium carbonate powder is added into the reaction kettle, and after stirring for a certain time, a conventional post-processing step of filtration, washing and drying is performed to obtain the aluminum-coated precursor particles. The whole process of the application only needs to be performed once, and the coating effect is good, no agglomeration phenomenon occurs, and the impurity sulfur content of the precursor is low. Therefore, the application has excellent production efficiency and a wide industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery materials, specifically relating to a method for preparing an aluminum-coated precursor. Background Technology

[0002] Cathode material LiNi x Co y Mn z O2 (x+y+z=1) has become one of the most popular cathode materials on the market due to its high capacity. Further optimization of its cycle performance is a research hotspot for this material. Al with suitable ionic radius and valence state... 3+ In cathode materials, it can enhance the stability of the layered structure. Coating the cathode material with it can also reduce side reactions between the active material and the electrolyte, mitigate irreversible phase transitions, and thus improve the cycle performance of the cathode material. High-quality precursor materials are fundamental to producing high-quality cathode materials. The co-precipitation method for preparing aluminum hydroxide-coated precursors offers advantages such as uniform elemental distribution and high particle consistency.

[0003] Aluminum hydroxide is an amphoteric hydroxide, forming under both acidic and alkaline conditions. Since the co-precipitation method for preparing precursors requires an alkaline reaction environment, alkaline AlO2 is commonly used. - Solution-based aluminum doping or coating modification is used, but this method suffers from problems such as easy agglomeration and incomplete precipitation of aluminum precipitates. Aluminum coating under acidic conditions requires the precursor powder to be reformulated into a slurry, which is a cumbersome process and may lead to an increase in the sulfur content of the precursor.

[0004] Both patents CN102306751B and CN103178258B prepare precursors via a co-precipitation method. After filtration, washing, and drying, the former prepares a precursor slurry with a certain solid content, adds an isopropanol solution containing a certain amount of aluminum isopropoxide to the slurry, and after the reaction is complete, it is filtered, washed, and dried again to obtain an aluminum isopropoxide-coated nickel-cobalt-manganese hydroxide precursor. The latter adds the precursor, soluble aluminum salt, and a dispersant to deionized water, stirs and heats, and finally washes and dries to obtain an aluminum hydroxide-coated nickel-cobalt-manganese hydroxide precursor. Both methods require two filtration, washing, and drying processes, which are cumbersome and have high costs for large-scale industrial production.

[0005] Patent CN107316990A synthesizes the precursor by co-precipitation, then directly adds sulfuric acid to the reaction slurry to lower the pH to 7.0-8.5, and then adds aluminum salt to hydrolyze it into aluminum hydroxide to coat the precursor surface. The precursor obtained by this method has a large number of small aluminum core particles on its surface, which fails to form a good microstructure. Furthermore, directly adding sulfuric acid to lower the pH of the reaction system can easily lead to excessive sulfur content in the precursor.

[0006] In conclusion, it is indeed necessary to provide a novel method for preparing aluminum-coated precursors with controllable coating amount, low impurity content, excellent morphology, and simple operation that is easy to mass-produce. Summary of the Invention

[0007] The purpose of this invention is to solve the above-mentioned problems in the prior art and to provide a novel method for preparing aluminum-coated precursors with controllable coating amount, low impurity content, excellent morphology, and simple operation that is easy to mass-produce.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for preparing an aluminum-coated precursor, wherein the method involves synthesizing a Ni alloy in a reaction vessel via a co-precipitation method. x Co y Mn z The precursor of (OH)₂ has x + y + z = 1, and 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1; an aluminum sulfate solution of a certain concentration and pH is prepared; the aluminum sulfate solution is added to the reaction vessel, controlling the appropriate addition rate, temperature, and stirring speed; after the addition is complete, a certain amount of sodium carbonate powder is added to the reaction vessel, and after stirring for a certain time, it undergoes conventional post-processing steps such as filtration, washing, and drying to obtain the aluminum-coated precursor. Specific steps include:

[0010] (1) Solution preparation: Prepare a metal salt solution of a certain concentration, wherein the metal salt is selected from at least one of nickel salt, cobalt salt, and manganese salt; prepare an aluminum sulfate solution of a certain concentration and pH; prepare a complexing agent solution and a precipitant solution of a certain concentration;

[0011] (2) Preparation of uncoated precursor by coprecipitation reaction: Metal salt solution, precipitant solution and complexing agent solution are simultaneously introduced into a reaction vessel containing bottom liquid to carry out coprecipitation reaction. During the reaction, the concentrator is turned on to drain the liquid, the liquid level in the reaction vessel is kept constant, and the reaction conditions are controlled as the first temperature, the first pH and the first stirring speed. A protective atmosphere is introduced during the reaction. After the target particle size is reached, the introduction of metal salt solution is stopped to obtain the uncoated precursor.

[0012] (3) Aluminum coating: Adjust the reactor conditions to the second temperature and the second stirring speed, and introduce the aluminum sulfate solution obtained in step (1) into the reactor at a low flow rate. The pH of the reactor decreases as the aluminum sulfate solution is added, and remains constant after decreasing to the target second pH. After introducing enough aluminum sulfate solution, stop introducing the aluminum sulfate solution and continue stirring for a certain period of time.

[0013] (4) Post-processing: Sodium carbonate powder is added to the reactor, and the reactor temperature is increased. After stirring for a certain period of time, the slurry in the reactor is passed into a washing tank for washing with pure water. After drying, it is sieved to obtain aluminum-coated Ni. x Co y Mn z (OH)2 spherical precursor particles, where x+y+z=1, and 0≤x≤1, 0≤y≤1, 0≤z≤1.

[0014] To better realize the present invention, furthermore, in step (1), the nickel salt, cobalt salt, and manganese salt are one or more combinations of the corresponding soluble sulfates, acetates, nitrates, and chlorides, and the total metal concentration of the metal salt solution is 1-3 mol / L, preferably 1.5-2 mol / L; the metal ratio in the metal salt solution conforms to Ni x Co y Mn z , x+y+z=1, and 0≤x≤1, 0≤y≤1, 0≤z≤1;

[0015] To better realize the present invention, further, in step (1), the concentration of aluminum sulfate solution is 0.2-1.5 mol / L, preferably 0.5-1 mol / L, and the pH is adjusted to 1-2.5, preferably 1.5-2. The pH is preferably adjusted by dilute sulfuric acid, and the concentration of dilute sulfuric acid is preferably 2-5 mol / L.

[0016] To better realize the present invention, further, in step (1), the precipitant solution is one or a combination of potassium hydroxide solution, lithium hydroxide solution and sodium hydroxide solution, and the concentration of the precipitant is 1-12 mol / L, preferably 5-10 mol / L; the complexing agent solution is one or a combination of ammonia water, ammonium chloride, EDTA and ammonium bicarbonate, and the concentration of the complexing agent is 1-12 mol / L, preferably 5-10 mol / L.

[0017] To better realize the present invention, further, in step (2), the pH and temperature of the bottom liquid in the reactor are kept consistent with the first pH and first temperature of the reaction. The first reaction temperature is controlled at 45-75℃, preferably 50-70℃, the first pH of the reaction process is 9-13, preferably 10-12, the metal salt solution introduced per hour is 1 / 100 to 1 / 20 of the reactor volume, preferably 1 / 50 to 1 / 25, and the first stirring speed is 150-800 rpm, preferably 200-600 rpm. More preferably, the ammonia value of the bottom liquid and the reaction system is controlled to be 2.5-3.5 g / L by adding a complexing agent.

[0018] To better realize the present invention, further, the target particle size D50 in step (2) is 8-15 μm.

[0019] To better realize the present invention, furthermore, in step (3), the second temperature is maintained at 30-45℃, preferably 35-40℃, the second stirring speed is 50-400rpm, preferably 100-200rpm, and the solid content in the reactor is 200-600g / L, preferably 300-500g / L. The second stirring speed for aluminum coating is lower than the first stirring speed for the co-precipitation reaction, so as to allow aluminum to grow better on the particle surface.

[0020] To better realize the present invention, in step (3), the amount of aluminum element introduced is 1000-5000 ppm of the precursor particles, preferably 2000-4000 ppm.

[0021] To better realize the present invention, further, the flow rate of aluminum sulfate solution in step (3) is 1 / 5 of the flow rate of metal salt solution in step (2), and the target second pH is maintained at 8.8-9.4, preferably 9-9.2; preferably, when the pH drops to a certain level, a precipitant solution is introduced to maintain a constant pH; preferably, stirring is continued for no less than 1 hour after stopping the introduction of aluminum sulfate solution.

[0022] To better realize the present invention, in step (4), sodium carbonate powder is added to make the sodium carbonate concentration in the reactor 0.5-2 mol / L, preferably 1-1.5 mol / L; the stirring speed is 40-300 rpm, preferably 80-150 rpm; and the stirring time is preferably 2-6 h, more preferably 4 h.

[0023] To better realize the present invention, further, in step (4), the temperature of the reactor is increased to 70°C.

[0024] To better realize the present invention, in step (4), the slurry is further washed with pure water in a washing tank until the pH is below 8.

[0025] To better realize the present invention, the protective atmosphere described in the present invention is preferably at least one of nitrogen, helium, and argon.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] (1) The method of coating aluminum precursors described in this invention does not require two washing, filtering and drying processes. After the target particle size is reached in the reactor, the coating operation can be carried out by simply changing the temperature, which simplifies the process and reduces production costs.

[0028] (2) The method described in this invention can achieve aluminum coating on the surface of the precursor, with uniform aluminum element distribution, good coating effect, no agglomeration, and easy control of the amount of aluminum introduced. Adding dilute sulfuric acid to the molten aluminum serves two purposes: first, it stabilizes the aluminum in the molten aluminum and inhibits its hydrolysis; second, when molten aluminum is introduced into the reactor, it lowers the pH of the reactor to a suitable range for coating. During the reaction, the aluminum content in the clear liquid is 0, ensuring that all aluminum participates in the precipitation.

[0029] (3) The method described in this invention relates to the post-processing of the precursor after aluminum coating. The newly generated aluminum hydroxide is easily soluble in alkaline solution. It is aged using sodium carbonate, which reduces the sulfur content of the impurities and prevents the dissolution of aluminum hydroxide from causing inaccurate coating amount. Attached Figure Description

[0030] Figure 1 This is a SEM image of the aluminum-coated precursor in Example 1;

[0031] Figure 2 EDS image of the aluminum-coated precursor in Example 1;

[0032] Figure 3 This is a SEM image of the aluminum-coated precursor in Example 2;

[0033] Figure 4 This is a SEM image of the aluminum-coated precursor in Example 3;

[0034] Figure 5 Here is a SEM image of the aluminum-coated precursor in Comparative Example 1;

[0035] Figure 6 Here is a SEM image of the aluminum-coated precursor in Comparative Example 2;

[0036] Figure 7 The image shows the SEM image of the aluminum-coated precursor in Comparative Example 3. Detailed Implementation

[0037] To facilitate understanding, the technical solutions and implementation methods of the present invention will be further described clearly, completely, and in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the embodiments described herein are implemented based on the technical solutions of the present invention, providing detailed implementation methods and specific operating procedures, but are only some embodiments of the present invention, not all embodiments. The specific implementation methods described are limited to illustrative purposes and do not limit the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0038] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the materials and reagents used in the examples are commercially available unless otherwise specified.

[0039] Example 1

[0040] (1) Prepare a mixed metal salt solution by mixing NiSO4, CoSO4 and MnSO4 in a ratio of 0.9:0.06:0.04, with a total metal ion concentration of 2 mol / L; prepare a 0.5 mol / L Al2(SO4)3 solution and add dilute sulfuric acid to adjust the pH to 1.5; prepare a 5 mol / L sodium hydroxide solution as a precipitant; and prepare a 10 mol / L ammonia solution as a complexing agent.

[0041] (2) Add a base liquid with pH 10-12 to a 1000L reactor, set the temperature to 60℃, introduce nitrogen into the reactor to maintain the atmosphere, and simultaneously introduce a metal mixed salt solution, precipitant and complexing agent to carry out a co-precipitation reaction. The flow rate of the metal mixed solution is 50L / h. During the reaction, turn on the concentrator to drain the solution and keep the liquid level in the reactor constant. During the reaction, control the pH to 10-12 and the stirring speed to 300rpm. After reacting for a period of time until the particle size reaches 13.5μm, stop introducing the solution, reduce the stirring speed to 100rpm, and reduce the temperature to 40℃. At this time, the solid content in the reactor is 500g / L.

[0042] (3) Aluminum sulfate solution is introduced into the reactor at a flow rate of 10 L / h. Stirring is maintained. The pH in the reactor continues to decrease. When it drops to 9, a precipitant is introduced to maintain a constant pH. At this time, the aluminum content of the slurry is tested and found to be 0. The solution is introduced until the amount of aluminum is 2000 ppm of the precursor particles. Stirring is then maintained for one hour.

[0043] (4) Add sodium carbonate powder to the reactor to make the sodium carbonate concentration in the reactor 1 mol / L. At the same time, raise the temperature of the reactor to 70℃ and reduce the stirring speed to 80 rpm. After stirring for four hours, pass the slurry in the reactor into a washing tank and wash it with pure water until the pH is below 8. Then, after drying and sieving, obtain the N of aluminum coating. i0.90 Co 0.06 Mn 0.04 (OH)2 spherical precursor particles.

[0044] The sulfur content of the precursor obtained in Example 1 was 0.2614 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 1989 ppm as measured by ICP, which meets the design requirements.

[0045] Figure 1 This is a SEM image of the aluminum-coated precursor in Example 1. Figure 2The image shows the EDS diagram of the aluminum-coated precursor in Example 1, which shows that aluminum is uniformly distributed on the surface of the precursor.

[0046] Example 2

[0047] (1) Prepare a metal mixed solution by mixing NiSO4, CoSO4 and MnSO4 in a ratio of 0.9:0.06:0.04, with a metal ion concentration of 2 mol / L; prepare a 1 mol / L Al2(SO4)3 solution and add dilute sulfuric acid to adjust the pH to 1.8; prepare a 5 mol / L sodium hydroxide solution as a precipitant; and prepare a 10 mol / L ammonia solution as a complexing agent.

[0048] (2) Add a base liquid with pH 10-12 to a 1000L reactor, set the temperature to 60℃, introduce nitrogen into the reactor to maintain the atmosphere, and simultaneously introduce a metal mixed solution, precipitant and complexing agent to carry out a co-precipitation reaction. The flow rate of the metal mixed solution is 50L / h. During the reaction, turn on the concentrator to drain the liquid and keep the liquid level in the reactor constant. During the reaction, control the pH to 10-12 and the stirring speed to 300rpm. After reacting for a period of time until the particle size reaches 13.5μm, stop introducing the solution, reduce the stirring speed to 200rpm, and reduce the temperature to 40℃. At this time, the solid content in the reactor is 300g / L.

[0049] (3) Aluminum sulfate solution is introduced into the reactor at a flow rate of 10 L / h. Stirring is maintained. The pH in the reactor continues to decrease. When it drops to 9.2, a precipitant is introduced to maintain a constant pH. The solution is introduced until the amount of aluminum is 2000 ppm of the precursor particles. Then the solution is stopped and stirring is maintained for one hour.

[0050] (4) Add sodium carbonate powder to the reactor to make the sodium carbonate concentration in the reactor 1.5 mol / L. At the same time, raise the temperature of the reactor to 70℃ and reduce the stirring speed to 150 rpm. After stirring for four hours, pass the slurry in the reactor into a washing tank and wash it with pure water until the pH is below 8. Then dry and sieve to obtain the N of aluminum coating. i0.90 Co 0.06 Mn 0.04 (OH)2 spherical precursor particles.

[0051] The sulfur content of the precursor obtained in Example 2 was 0.2665 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 1996 ppm as measured by ICP, which meets the design requirements.

[0052] Figure 3 This is a SEM image of the aluminum-coated precursor in Example 2.

[0053] Example 3

[0054] (1) Prepare a metal mixed solution by mixing NiSO4, CoSO4 and MnSO4 in a ratio of 0.9:0.06:0.04, with a metal ion concentration of 2 mol / L; prepare a 0.5 mol / L Al2(SO4)3 solution and add dilute sulfuric acid to adjust the pH to 2; prepare a 5 mol / L sodium hydroxide solution as a precipitant; and prepare a 10 mol / L ammonia solution as a complexing agent.

[0055] (2) Add a base liquid with pH 10-12 to a 1000L reactor, set the temperature to 60℃, introduce nitrogen into the reactor to maintain the atmosphere, and simultaneously introduce a metal mixed solution, precipitant and complexing agent to carry out a co-precipitation reaction. The flow rate of the metal mixed solution is 50L / h. During the reaction, turn on the concentrator to drain the liquid and keep the liquid level in the reactor constant. During the reaction, control the pH to 10-12 and the stirring speed to 300rpm. After reacting for a period of time until the particle size reaches 13.5μm, stop introducing the solution, reduce the stirring speed to 150rpm, and reduce the temperature to 35℃. At this time, the solid content in the reactor is 400g / L.

[0056] (3) Aluminum sulfate solution is introduced into the reactor at a flow rate of 10 L / h. Stirring is maintained. The pH in the reactor continues to decrease. When it drops to 9, a precipitant is introduced to maintain a constant pH. The solution is introduced until the amount of aluminum is 4000 ppm of the precursor particles. Then the solution is stopped and stirring is maintained for one hour.

[0057] (4) Add sodium carbonate powder to the reactor to make the sodium carbonate concentration in the reactor 1.2 mol / L. At the same time, raise the temperature of the reactor to 70℃ and reduce the stirring speed to 100 rpm. After stirring for four hours, pass the slurry in the reactor into a washing tank and wash it with pure water until the pH is below 8. Then, after drying and sieving, obtain the N of aluminum coating. i0.90 Co 0.06 Mn 0.04 (OH)2 spherical precursor particles.

[0058] The sulfur content of the precursor obtained in Example 2 was 0.2735 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 4013 ppm as measured by ICP, which meets the design requirements.

[0059] Figure 4 This is a SEM image of the aluminum-coated precursor in Example 3.

[0060] Comparative Example 1

[0061] The only difference from Example 1 is that the concentration of aluminum sulfate solution in step (1) is 3 mol / L.

[0062] The sulfur content of the precursor obtained in Comparative Example 1 was 0.2587 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 1965 ppm as measured by ICP, which meets the design requirements.

[0063] Figure 5 The image shows an SEM image of the aluminum-coated precursor in Comparative Example 1. It can be seen that a higher concentration of aluminum sulfate leads to agglomeration on the particle surface. This may be because aluminum hydroxide has a lower Ksp, and aluminum is more likely to agglomerate at the feed inlet and adhere to the surface of the precursor particles.

[0064] Comparative Example 2

[0065] The only difference from Example 1 is that the temperature was not lowered after the reaction stopped in step (2), and remained at 60°C.

[0066] The sulfur content of the precursor obtained in Comparative Example 2 was 0.2584 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 1986 ppm as measured by ICP, which meets the design requirements.

[0067] Figure 6 The image shows the SEM image of the aluminum-coated precursor in Comparative Example 2. It can be seen from the image that when the aluminum coating temperature is high, some aluminum agglomeration is likely to occur.

[0068] Comparative Example 3

[0069] The only difference from Example 1 is that in step (1), the aluminum sulfate solution is not adjusted with dilute sulfuric acid.

[0070] The sulfur content of the precursor obtained in Comparative Example 3 was 0.2459 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. The aluminum content was 1256 ppm as measured by ICP, which does not meet the design requirements. This is because some aluminum hydrolysis occurred in the aluminum liquid, and the pH in the reactor could not be lowered to a range suitable for aluminum hydrolysis, resulting in a large number of free aluminum ions in the slurry clear liquid.

[0071] Figure 7 The image shows the SEM image of the aluminum-coated precursor in Comparative Example 3. The coating effect is good, but it is difficult to accurately control the amount of aluminum hydroxide coating layer generated.

[0072] Comparative Example 4

[0073] The only difference from Example 1 is that after stopping the reaction in step (2), dilute sulfuric acid is added to the reactor to adjust the pH to 9.

[0074] The sulfur content of the precursor obtained in Comparative Example 4 was 0.5256 wt% as measured by a carbon-sulfur analyzer, which did not meet the standard range. The aluminum content was 1991 ppm as measured by ICP, which met the design requirements.

[0075] Comparative Example 5

[0076] The only difference from Example 1 is that in step (4), NaOH solution commonly used in the industry is used for alkaline washing.

[0077] The precursor obtained in Comparative Example 5 had a sulfur content of 0.2476 wt% as measured by a carbon-sulfur analyzer, which is within the standard range. However, the aluminum content, as determined by ICP testing, was 1752 ppm, which does not meet the design requirements. This is because the newly generated aluminum hydroxide is easily soluble in strongly alkaline solutions, resulting in a loss of coating and reducing the utilization rate of aluminum.

[0078] As can be seen from the above embodiments and comparative examples, the method for preparing an aluminum-coated precursor provided by the present invention achieves uniform deposition of aluminum hydroxide on the surface of the precursor to form a uniform coating layer with good coating effect and excellent morphology. Furthermore, the use of sodium carbonate alkaline washing effectively reduces the sulfur content of the precursor impurities and prevents inaccurate coating amount caused by the dissolution of aluminum hydroxide. Compared with traditional methods, it also reduces one washing, filtering and drying process, thus playing a role in cost reduction and efficiency improvement for ternary precursor enterprises.

[0079] Finally, it should be noted that the above are preferred embodiments of the present invention. The present invention is not limited to the above embodiments. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an aluminum-coated precursor, characterized in that, The method involves synthesizing Ni using a co-precipitation method within a reaction vessel. x Co y Mn z The precursor of (OH)2, x+y+z=1, and 0≤x≤1, 0≤y≤1, 0≤z≤1; prepare an aluminum sulfate solution with a certain concentration and pH. Aluminum sulfate solution is added to a reaction vessel, with appropriate addition rate, temperature, and stirring speed controlled. After addition, sodium carbonate is added to the reaction vessel for alkaline washing, followed by post-treatment to obtain the aluminum-coated precursor. The process includes the following steps: (1) Solution preparation: Prepare a metal salt solution of a certain concentration, wherein the metal salt is selected from at least one of nickel salt, cobalt salt, and manganese salt; prepare an aluminum sulfate solution of a certain concentration and pH; prepare a complexing agent solution and a precipitant solution of a certain concentration; (2) Preparation of uncoated precursor by coprecipitation reaction: Metal salt solution, precipitant solution and complexing agent solution are simultaneously introduced into a reaction vessel containing bottom liquid to carry out coprecipitation reaction. During the reaction, the concentrator is turned on to drain the liquid, the liquid level in the reaction vessel is kept constant, and the reaction conditions are controlled as the first temperature, the first pH and the first stirring speed. A protective atmosphere is introduced during the reaction. After the target particle size is reached, the introduction of metal salt solution is stopped to obtain the uncoated precursor. (3) Aluminum coating: Adjust the reactor conditions to the second temperature and the second stirring speed, and introduce the aluminum sulfate solution from step (1) into the reactor at a low flow rate. The pH in the reactor decreases as the aluminum sulfate solution is added, and remains constant after decreasing to the target second pH. After introducing enough aluminum sulfate solution, stop introducing the aluminum sulfate solution and continue stirring for a certain period of time. (4) Post-treatment: Sodium carbonate is added to the reactor, and the reactor temperature is increased. After stirring for a certain period of time, aluminum-coated Ni is obtained through post-treatment. x Co y Mn z (OH)2 spherical precursor particles, where x+y+z=1, and 0≤x≤1, 0≤y≤1, 0≤z≤1; In step (1), the concentration of the aluminum sulfate solution is 0.2-1.5 mol / L, and the pH is adjusted to 1-2.5 by diluting sulfuric acid. In step (2), the first temperature is 45-75℃, the first pH is 9-13, the metal salt solution introduced per hour is 1 / 100 to 1 / 20 of the reactor volume, and the first stirring speed is 150-800 rpm. In step (3), the second temperature is 30-45℃, the second stirring speed is 50-400rpm, the second pH is maintained at 8.8-9.4, and the solid content in the reactor is 200-600g / L.

2. The method for preparing the aluminum-coated precursor according to claim 1, characterized in that, In step (1), the nickel salt, cobalt salt and manganese salt are at least one of the corresponding sulfate, acetate, nitrate and chloride salts, and the total metal concentration of the metal salt solution is 1-3 mol / L.

3. The method for preparing the aluminum-coated precursor according to claim 1, characterized in that, In step (1), the precipitant solution is at least one of potassium hydroxide solution, lithium hydroxide solution and sodium hydroxide solution, and the concentration of the precipitant is 1-12 mol / L; the complexing agent solution is at least one of ammonia water, ammonium chloride, EDTA and ammonium bicarbonate, and the concentration of the complexing agent is 1-12 mol / L.

4. The method for preparing the aluminum-coated precursor according to claim 1, characterized in that, In step (2), the target particle size D50 is 8-15 μm.

5. The method for preparing the aluminum-coated precursor according to claim 1, characterized in that, In step (3), the amount of aluminum introduced is 1000-5000 ppm of the precursor particles, and the flow rate of the aluminum sulfate solution introduced is 1 / 5 of the flow rate of the metal salt solution introduced in step (2).

6. The method for preparing the aluminum-coated precursor according to claim 1, characterized in that, In step (4), sodium carbonate is added to make the sodium carbonate concentration in the reactor 0.5-2 mol / L, the stirring speed is 40-300 rpm, the stirring time is 2-6 h, and the reactor temperature is increased to 70℃.

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