Preparation method of modified gradient aluminum-coated lithium ion battery positive electrode material precursor

Abstract

The invention discloses a preparation method of a modified gradient-coated aluminum lithium ion battery positive electrode material precursor, which comprises the following steps of: designing a composite structure of inner layer gradient-doped aluminum and outer layer coated aluminum, namely three stages, namely a crystal nucleus aluminum-free region, a crystal growth gradient aluminum region and a crystal outer layer coated aluminum region, so as to prepare the modified gradient-coated aluminum lithium ion battery positive electrode material precursor. An Al source is infiltrated into pores of the lithium ion battery positive electrode material precursor through liquid phase deposition, and gradient Al distribution in the pores is formed. The content of aluminum doped in crystal growth is changed from low to high, and the purpose is that the internal gradient is a stable crystal lattice, the crystal lattice stress in the charging and discharging process is relieved, and cracks are inhibited, so that the thermal cycling stability is effectively improved; the Al coated on the outer layer of the crystal can effectively inhibit the contact between the electrolyte and the active material, reduce the side reaction of the interface, increase the interface stability and reduce the gas production in the charge-discharge process, thereby obviously enhancing the electrochemical performance of the battery.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery cathode material, and particularly relates to a preparation method of a modified gradient aluminum-coated lithium ion battery cathode material precursor. BACKGROUND

[0002] With the enhancement of people's environmental protection consciousness and the increasingly serious energy crisis, people's desire for new energy development is also increasingly strengthened. At the same time, with the progress of science and technology, electronic devices on the market are increasing, and the types are also increasingly diversified. The traditional battery has been difficult to meet people's current needs, and more and more people turn their eyes to the lithium battery industry. Although there are various types of precursors of cathode materials on the market at present, lithium ion batteries are still dominant, and the performance of the cathode material of the battery is not only to pursue high power and thermal stability, but also to have high capacity, good cycle performance, high voltage, high capacity and good cycle performance. The existing high-voltage lithium ion battery cathode material (such as high-nickel NCM and lithium-rich manganese-based material) is prone to electrolyte decomposition, transition metal dissolution, lattice oxygen loss and other problems under high voltage, resulting in battery capacity attenuation and thermal stability decline. The traditional surface coating (such as Al2O3) is mostly non-uniform coating, which cannot effectively fill the precursor pores, resulting in poor interfacial adhesion between the coating layer and the substrate, and easy cracking during long-term cycle use.

[0003] The patent document CN103178262A discloses a preparation method of aluminum-doped lithium nickel cobalt oxide. Soluble salt solutions of nickel and cobalt, ammonia water and alkali solution are simultaneously added to a reaction kettle for co-precipitation reaction. By controlling the process parameters in the preparation process, nickel-cobalt hydroxide precursor is synthesized. The nickel-cobalt hydroxide precursor obtained by the above reaction is washed to a certain condition, and a soluble aluminum salt solution is added thereto. By controlling the process parameters in the reaction process, nickel-cobalt-aluminum hydroxide precursor is synthesized. The patent technology discloses a method for preparing nickel-cobalt-aluminum hydroxide precursor by step-by-step precipitation method. The prepared nickel-cobalt-aluminum hydroxide precursor has a spherical or spherical-like morphology. However, the aluminum doping process is essentially surface-coated with aluminum to form a coating layer, which cannot effectively fill the precursor pores, resulting in poor interfacial adhesion between the coating layer and the substrate, and easy cracking during long-term cycle use.

[0004] The patent document CN106935844A discloses a preparation method of a lithium ion battery positive electrode material. A salt solution, an aluminum-containing alkaline solution and a complexing agent solution are added into a reaction kettle with overflow port to react, and the overflow obtained precursor slurry is subjected to solid-liquid separation, washing, drying, and screening to obtain a positive electrode material precursor, which is then mixed with a lithium source, sintered, crushed, and screened to obtain a uniformly aluminum-doped positive electrode material. This method can realize uniform doping of aluminum elements in the precursor, and has the advantages of simple process, smooth flow, low production cost, and suitability for large-scale industrial production. However, since the patent technology continuously passes through a constant concentration of aluminum-containing alkaline solution at the initial stage of the precursor co-precipitation reaction, aluminum will replace part of nickel in the early stage of crystal nucleus formation, reducing the nickel content in the crystal nucleus and affecting the battery capacity performance. In addition, the constant concentration continuous feeding doping method cannot effectively stabilize the crystal structure, which will affect the cycle stability performance of the lithium ion battery to some extent.

[0005] The patent document CN109896552A discloses a preparation method of an aluminum-doped lithium ion positive electrode material precursor. A cobalt solution, ammonia water and aluminum complex solution mixed solution are added into a reaction kettle from one side of the reaction kettle, and a liquid alkali solution is added into the reaction kettle from the other side of the reaction kettle in a metering manner. The solution added into the reaction kettle is stirred and mixed by a spiral stirring impeller, and the pH value of the solution is controlled to about 12.4. The uniformly mixed solution in the reaction kettle is left still, the supernatant is filtered into an aging tank, and the aged reaction product is sintered and mixed to remove magnetic treatment to obtain a finished aluminum-doped cobalt oxide precursor. However, since the patent technology continuously passes through a constant concentration of aluminum-containing alkaline solution at the initial stage of the precursor co-precipitation reaction, aluminum will replace part of nickel in the early stage of crystal nucleus formation, reducing the nickel content in the crystal nucleus and affecting the battery capacity performance. In addition, the constant concentration continuous feeding doping method cannot effectively stabilize the crystal structure, which will affect the cycle stability performance of the lithium ion battery to some extent.

[0006] The patent document CN202411582102.9 discloses a preparation method and application of an aluminum-doped lithium battery positive electrode material precursor. An aluminum salt and one or more of a nickel salt, a cobalt salt and a manganese salt are dissolved in water to prepare a mixed metal solution, and another aluminum salt is selected to prepare an aluminum-alkali solution with lye as a solvent. The mixed metal solution and the aluminum-alkali solution are fed at a certain proportion of feeding speed, and the precursor is prepared by a co-precipitation method, which can effectively improve the sphericity of the precursor, make the particle size distribution more uniform and consistent, and be beneficial to improving the electrochemical performance of the positive electrode material. At the same time, by adding an additive to the kettle bottom liquid to reduce the formation of small balls in the preparation process of the precursor, the length-width ratio of the primary particles is controlled and the sphericity is improved, and the particle size distribution of the precursor is more uniform and consistent. However, due to the constant concentration of the aluminum-containing alkaline solution in the initial stage of the precursor co-precipitation reaction, the aluminum will replace part of the nickel in the initial stage of crystal nucleus formation, reducing the nickel content in the crystal nucleus and affecting the battery capacity performance. In addition, the constant concentration continuous feeding doping method cannot effectively stabilize the crystal structure, which will affect the cycle stability of the lithium ion battery to some extent.

[0007] Therefore, it has certain practical significance to develop a lithium ion battery positive electrode material with good cycle performance at high voltage, good high-temperature stability and high capacity. SUMMARY

[0008] The technical problem solved by the present application is to provide a preparation method of a modified gradient aluminum-coated lithium ion battery positive electrode material precursor. The method is designed with a composite structure of inner layer gradient aluminum doping and outer layer aluminum coating, i.e. three stages of aluminum-free zone, crystal growth gradient aluminum zone and crystal outer layer aluminum coating zone. Al source (such as NaAlO2, Al(NO3)3) is infiltrated into the pores of the lithium ion battery positive electrode material precursor (such as Ni-Co-Mn hydroxide) through liquid deposition, and gradient Al distribution is formed in the pores. The aluminum content in the crystal growth changes from low to high, which is to stabilize the crystal lattice, relieve the lattice stress in the charging and discharging process, and inhibit the generation of cracks, so as to effectively improve the thermal cycle stability. The crystal outer layer coated with Al can effectively inhibit the contact between the electrolyte and the active material, reduce the interface side reaction, increase the interface stability, reduce the gas production in the charging and discharging process, and thus significantly improve the electrochemical performance of the battery.

[0009] The application mainly adopts the co-deposition method to uniformly distribute Al in the positive material precursor, and the difference between the application and the previous co-deposition of Al is that the co-deposition reaction process is divided into three stages, the first stage is a crystal nucleation zone with a particle size of 1.5-2 μm, which does not contain Al, has a high nickel content, and retains high capacity inside; the second stage is a crystal growth zone with a particle size of 2-4 μm, which gradually increases the Al source content by adding the Al source, and the Al source content changes in a gradient manner, the purpose is to stabilize the crystal structure and prevent the crystal structure from collapsing in the charging and discharging process, thereby effectively improving the thermal cycle stability; the third stage is an Al coating zone, which can inhibit the phase change of the body phase, can refine the surface particles, make the surface particles porous, reduce the gas production in the charging and discharging process, and improve the battery safety performance.

[0010] The application adopts the following technical scheme to solve the above technical problems, a preparation method of a modified gradient aluminum-coated lithium ion battery positive material precursor, the specific preparation steps are: Step S1, prepare a nickel-cobalt-manganese mixed salt solution, a complexing agent solution and a precipitant solution respectively, dissolve aluminum salt in excess alkali solution to prepare an aluminum-alkali solution, wherein the aluminum salt is one or more of aluminum sulfate, sodium metaaluminate and aluminum nitrate, and the alkali solution is sodium hydroxide solution or potassium hydroxide solution; Step S2, add a mixed solution of the precipitant solution, the complexing agent solution and pure water to the reaction kettle and continuously introduce protective gas, then add the nickel-cobalt-manganese mixed salt solution, the precipitant solution and the complexing agent solution into the reaction kettle through the precision metering pump for co-deposition reaction, when the particle size grows to 1.5-2 μm, stop the precipitant solution, and add the aluminum-alkali solution into the reaction kettle through the precision metering pump, this stage is an aluminum-free crystal nucleation zone; when the particle size grows to 2.5-4 μm, increase the flow rate of the aluminum-alkali solution in a gradient manner until the particle size grows to the target particle size, stop the reaction, and this stage is an aluminum gradient-doped crystal growth zone; the reaction slurry obtained by the reaction is subjected to solid-liquid separation to obtain the dehydrated precursor slurry; Step S3, put the dehydrated precursor slurry into the reaction kettle, control the material-water ratio to be 2:3, add the aluminum-alkali solution into the reaction kettle through the precision metering pump, this stage is the aluminum coating layer formation stage, wash the material after coating, and obtain the dehydrated material after solid-liquid separation, then dry at 100-150 ℃ to obtain the modified gradient aluminum-coated lithium ion battery positive material precursor.

[0011] The preparation method of the modified gradient aluminum-coated lithium ion battery positive material precursor is as follows: Step S1, respectively prepare nickel-cobalt-manganese mixed salt solution, complexing agent solution and precipitant solution, dissolve aluminum salt in excess of alkali liquor to prepare aluminum-alkali solution I and aluminum-alkali solution II with different concentrations, wherein the aluminum salt is one or more of aluminum sulfate, sodium metaaluminate and aluminum nitrate, and the alkali liquor is sodium hydroxide solution or potassium hydroxide solution; Step S2, add the mixed solution of the precipitant solution, the complexing agent solution and pure water into the reaction kettle and continuously pass the protective gas, then punch the nickel-cobalt-manganese mixed salt solution, the precipitant solution and the complexing agent solution into the reaction kettle through the precision metering pump for co-deposition reaction, when the particle size grows to 1.5-2 μm, stop the precipitant solution, punch the aluminum-alkali solution I into the reaction kettle through the precision metering pump, this stage is the crystal nucleation zone without aluminum, when the particle size grows to 2.5-4 μm, punch the aluminum-alkali solution II into the container of the aluminum-alkali solution I through the precision metering pump, the concentration of the aluminum-alkali solution II is greater than that of the aluminum-alkali solution I, the flow ratio of the aluminum-alkali solution II to the aluminum-alkali solution I is 1:2-4, until the particle size grows to the target particle size, stop the reaction, this stage is the crystal growth zone with aluminum gradient doping, the temperature of the reaction kettle is 30-80℃ during the whole reaction process, the pH of the mixed system in the reaction kettle is 9-13, the concentration of the complexing agent in the reaction kettle is 1-20 g / L, and the stirring rate is 200-1000 rpm, then the reaction slurry obtained by the reaction is subjected to solid-liquid separation to obtain the dehydrated precursor slurry; Step S3, put the dehydrated precursor slurry into the reaction kettle, control the material-water ratio to be 2:3, separately punch the aluminum-alkali solution I into the reaction kettle through the precision metering pump, this stage is the aluminum coating layer formation stage, the pH of the mixed system in the reaction kettle is 9-11 during the whole reaction process, the reaction temperature is 40-60℃, and the stirring rate is 200-500 rpm, then the material after coating is washed with water and subjected to solid-liquid separation to obtain the dehydrated material, and the modified gradient aluminum-coated lithium ion battery positive electrode material precursor is obtained by drying at 100-150℃.

[0012] Further limitation, the total metal concentration of the nickel-cobalt-manganese mixed salt solution in step S1 is 1.5-2.5 mol / L, the nickel-cobalt-manganese mixed salt solution is compounded by soluble nickel salt, soluble cobalt salt and soluble manganese salt and water; the complexing agent solution is ammonia water solution with a concentration of 1-10 mol / L; and the precipitant solution is sodium hydroxide solution or potassium hydroxide solution with a concentration of 1-8 mol / L.

[0013] Further limitation, the concentration of the aluminum-alkali solution I in step S2 is 0.02-0.04 mol / L, and the concentration of the aluminum-alkali solution II is 0.08-0.10 mol / L.

[0014] Further limited, the aluminum-alkali solution I in step S2 is an aluminum-alkali solution with a concentration of 0.03 mol / L obtained by adding 2.5 g of sodium metaaluminate into 1 L of 4 mol / L sodium hydroxide solution; the aluminum-alkali solution II is an aluminum-alkali solution with a concentration of 0.09 mol / L obtained by adding 7.5 g of sodium metaaluminate into 1 L of 4 mol / L sodium hydroxide solution; the flow rate ratio of the aluminum-alkali solution II to the aluminum-alkali solution I is 1:3.

[0015] Further limited, the modified gradient-coated-aluminum lithium ion battery cathode material precursor in step S3 has a molecular formula of Ni X Co Y Mn 1-X-Y-Z Al Z (OH)2, wherein 0.5 < X < 1, 0.01 < Y < 0.2, 0.01 ≤ Z < 0.05, and X + Y + Z < 1.

[0016] Compared with the prior art, the present application has the following obvious beneficial effects and advantages: (1) Different from the previous aluminum doping method, the present application adopts co-deposition to make the aluminum element uniformly distributed, and forms no aluminum crystal nucleus, grows a gradient aluminum-doped crystal, and coats the aluminum on the surface of the crystal in the precursor synthesis stage. The precursor prepared by this method has uniform primary particles, high tap density, and large specific surface area.

[0017] (2) The modified gradient-coated-aluminum lithium ion battery cathode material precursor prepared by the present application has high crystallinity and stable structure. The lithium ion cathode material prepared by sintering has aluminum element replacing part of the transition metals Ni / Co / Mn. Due to the high bond energy (Al-O bond is stronger than Ni / Co-O), the lattice distortion in the charging and discharging process can be inhibited, the phase change can be reduced, and the cycle life can be prolonged. A layer of aluminum is coated on the outer layer, and the surface Al-rich layer inhibits the oxidative decomposition of the electrolyte, reduces the generation of gas by-products (such as CO2) of high-nickel materials at high temperature or overcharging, and improves the thermal stability and safety of the material. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 SEM image of the precursor prepared in Example 1.

[0019] Figure 2 SEM image of the precursor prepared in Comparative Example 1.

[0020] Figure 3 SEM image of the precursor prepared in Comparative Example 2.

[0021] Figure 4 Cycle comparison curve of the lithium ion battery assembled by sintering the precursors prepared in Example 1 and Comparative Examples 1-2.

[0022] Figure 5 Discharge cycle, capacity comparison curves of lithium ion batteries assembled by sintering the precursors prepared in Example 1 and Comparative Examples 3-4 were prepared. DETAILED DESCRIPTION

[0023] The above content of the present application is further illustrated in detail by the following examples, but this should not be understood as the scope of the above subject matter of the present application being limited to the following examples only, and any technology realized based on the above content of the present application falls within the scope of the present application. EXAMPLE

[0024] Step S1: a nickel-cobalt-manganese mixed salt solution with a total metal concentration of 1.8 mol / L was prepared using nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of nickel, cobalt and manganese was 93.88:4.08:2.04; sodium metaaluminate was added to a prepared 4 mol / L sodium hydroxide solution to form a sodium metaaluminate-sodium hydroxide mixed solution, and the specific preparation process was that 2.5 g of sodium metaaluminate was added to 1 L of 4 mol / L sodium hydroxide solution to prepare an aluminum-alkali solution I with a concentration of 0.03 mol / L, and 7.5 g of sodium metaaluminate was added to 1 L of 4 mol / L sodium hydroxide solution to prepare an aluminum-alkali solution II with a concentration of 0.09 mol / L; an ammonia solution with a concentration of 6 mol / L was prepared as a complexing agent solution, and a 4 mol / L sodium hydroxide solution was prepared as a precipitating agent solution; Step S2: 78.6 L of pure water, 1.2 L of complexing agent solution and 0.2 L of precipitating agent solution were added to a reaction kettle to prepare a total volume of 80 L of a bottom solution, the pH value of the mixed system was adjusted to 12.3-12.4, the ammonia content was 2-3 g / L, and the temperature was controlled at 55°C. The stirring device was started, and the stirring rate was 850 r / min. Nitrogen was continuously introduced into the liquid surface of the reaction kettle at a rate of 5 L / min. The nickel-cobalt-manganese mixed salt solution, the complexing agent solution and the precipitating agent solution prepared above were added to the reaction kettle through three precision metering pumps for a first-stage nucleation zone aluminum-free co-precipitation reaction, the pH value was controlled at 12.2-12.3, when the particle size grew to 1.7 μm, the precipitating agent solution stopped flowing, the fourth precision metering pump was started to continuously feed the aluminum-alkali solution I for 2 h, and then the aluminum-alkali solution II was added to the container of the aluminum-alkali solution I through the precision metering pump, wherein the flow rate ratio of the aluminum-alkali solution I to the aluminum-alkali solution II was 3:1, the aluminum-alkali solution feeding concentration gradually increased, the pH value was controlled at 11.7-11.8, the flow rate of the nickel-cobalt-manganese mixed salt solution was 80 mL / min, and the flow rate of the aluminum-alkali solution I was 53.5 mL / min. The reaction temperature was 55°C, the ammonia content of the mixed system was 2-3 g / L, the stirring rate was 850 rpm, and the reaction was stopped when the particle size grew to 4 μm. The reaction slurry obtained by the reaction was subjected to solid-liquid separation to obtain a dehydrated precursor slurry. Step S3: The dehydrated precursor slurry is put into a reaction kettle, the material-water ratio is controlled to be 2:3, the aluminum-alkali solution I is pumped into the reaction kettle by a precision metering pump, the flow rate of the aluminum-alkali solution is 25.6 mL / min, this stage is an aluminum coating layer forming stage, the pH of the mixed system in the reaction kettle during the whole reaction process is 9.5-9.7, the reaction temperature is 50°C, the stirring rate is 450 rpm, the material after coating is washed with water, and the dehydrated material is obtained after solid-liquid separation, and then the material is dried at 110°C to obtain Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor.

[0025] Test: The Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor obtained above is subjected to scanning electron microscope test, Figure 1 The scanning electron microscope image of the precursor prepared for this example is shown in the figure, and it can be seen from the figure that the Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor prepared in this example has good sphericity and uniform primary particles; the D 50 of the precursor prepared in this example is 4.02 μm, the specific surface area thereof is 14.20 m 2 / g, and the tap density thereof is 1.85 g / cm 3 .

[0026] Comparative Example 1 (aluminum-alkali solution is added synchronously at the initial stage of coprecipitation reaction) Step S1: A nickel-cobalt-manganese mixed salt solution with a total metal concentration of 1.8 mol / L is prepared by using nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of nickel, cobalt and manganese is 93.88:4.08:2.04; sodium metaaluminate is added to the prepared 4 mol / L sodium hydroxide solution to form a sodium metaaluminate-sodium hydroxide mixed solution, and the specific preparation process is that 5 g of sodium metaaluminate is added to 1 L of 4 mol / L sodium hydroxide solution to prepare an aluminum-alkali solution with a concentration of 0.06 mol / L; a 6 mol / L ammonia solution is prepared as a complexing agent solution, and a 4 mol / L sodium hydroxide solution is prepared as a precipitant solution.

[0027] Step S2: 78.6 L of pure water, 1.2 L of complexing agent solution and 0.2 L of precipitant solution are added into a reaction kettle to prepare a total volume of 80 L of a base solution, the pH value of the mixed system is adjusted to 12.3-12.4, the ammonia content is 2-3 g / L, and the temperature is controlled at 55°C. The stirring device is started, and the stirring speed is 850 r / min. Nitrogen is continuously introduced into the liquid surface of the reaction kettle at a rate of 5 L / min. The above prepared nickel-cobalt-manganese mixed salt solution, aluminum-alkali solution, precipitant solution and complexing agent solution are added into the reaction kettle through four precision metering pumps for co-precipitation reaction. The reaction temperature is 55°C, the pH value is controlled at 11.7-11.8, the flow rate of the nickel-cobalt-manganese mixed salt solution is 80 mL / min, the flow rate of the aluminum-alkali solution is 53.5 mL / min, the ammonia content is 2-3 g / L, and the particle size is grown to 4.0 μm, and the reaction is stopped. The slurry obtained by the reaction is subjected to solid-liquid separation by centrifugation to obtain the dewatered precursor slurry; Step S3: The dewatered precursor slurry is put into a reaction kettle, the material to water ratio is controlled at 2:3, and the aluminum-alkali solution is introduced into the reaction kettle through a precision metering pump. The flow rate of the aluminum-alkali solution is 25.6 mL / min. This stage is the aluminum coating layer formation stage. The pH value of the mixed system in the reaction kettle is 9.5-9.7, the reaction temperature is 50°C, and the stirring rate is 450 rpm. The coated material is washed with water, and the dewatered material is obtained after solid-liquid separation. Then, the material is dried at 110°C to obtain the Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor.

[0028] Test: The Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor obtained above is subjected to scanning electron microscope test, Figure 2 The scanning electron microscope image of the precursor prepared in the example is shown in Figure 1. The D 50 of the precursor prepared in the example is 3.984 μm, the specific surface area is 10.22 m 2 / g, and the tap density is 1.75 g / cm 3 .

[0029] Comparative Example 2 (conventional aluminum sulfate solution instead of aluminum-alkali solution) Step S1: a nickel sulfate, cobalt sulfate and manganese sulfate, aluminum sulfate solution with a total metal concentration of 1.8 mol / L is prepared, wherein the molar ratio of nickel, cobalt, manganese and aluminum is 92.5:4:2:1.5; an ammonia solution with a concentration of 6 mol / L is prepared as a complexing agent solution, and a sodium hydroxide solution with a concentration of 4 mol / L is prepared as a precipitant solution.

[0030] Step S2: 78.6 L of pure water, 1.2 L of complexing agent solution and 0.2 L of precipitant solution are added to a reaction kettle to prepare a base solution with a total volume of 80 L, the pH value of the mixed system is adjusted to 12.3-12.4, the ammonia content is 2-3 g / L, and the temperature is controlled at 55°C. The stirring device is started, and the stirring speed is 850 r / min. Nitrogen is continuously introduced into the liquid surface of the reaction kettle at a rate of 5 L / min. The above-prepared nickel-cobalt-manganese-aluminum mixed salt solution, precipitant solution and complexing agent solution are added to the reaction kettle through three precision metering pumps for co-precipitation reaction. The reaction temperature is 55°C, the pH value is controlled at 11.7-11.8, the flow rate of the nickel-cobalt-manganese-aluminum mixed salt solution is 80 mL / min, the flow rate of the precipitant sodium hydroxide solution is 41.5 mL / min, the ammonia content is 2-3 g / L, and the particle size is grown to 3.91 μm. The reaction is stopped, and the obtained slurry is separated by centrifugation to obtain the precursor slurry after dehydration; Step S3: the precursor slurry after dehydration is put into the reaction kettle, the solid-liquid ratio is controlled at 2:3, and the aluminum sulfate solution is introduced into the reaction kettle through a precision metering pump. The flow rate of the aluminum sulfate solution is 25.6 mL / min. This stage is the aluminum coating layer formation stage. The pH value of the mixed system in the reaction kettle is 9.5-9.7, the reaction temperature is 50°C, and the stirring rate is 450 rpm. The coated material is washed with water, and the material after solid-liquid separation is dehydrated, and then dried at 110°C to obtain the Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor.

[0031] Test: the Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor obtained above is subjected to scanning electron microscope test, Figure 3 The scanning electron microscope image of the precursor prepared in the example is shown in Figure 1. The D 50 of the precursor prepared in the example is 3.935 μm, the specific surface area is 8.0 m 2 / g, and the tap density is 1.78 g / cm 3 .

[0032] Comparative Example 3 (constant addition of low concentration aluminum-alkali solution) Step S1: a nickel-cobalt-manganese mixed salt solution with a total metal concentration of 1.8 mol / L was prepared using nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of nickel, cobalt and manganese was 93.88:4.08:2.04; sodium metaaluminate was added to the prepared 4 mol / L sodium hydroxide solution to form a sodium metaaluminate-sodium hydroxide mixed solution, and the specific preparation process was that 2.5 g of sodium metaaluminate was added to 1 L of 2 mol / L sodium hydroxide solution to prepare an aluminum-alkali solution I with a concentration of 0.03 mol / L; an ammonia solution with a concentration of 6 mol / L was prepared as a complexing agent solution, and a 4 mol / L sodium hydroxide solution was prepared as a precipitant solution; Step S2: 78.6 L of pure water, 1.2 L of complexing agent solution and 0.2 L of precipitant solution were added to a reaction kettle to prepare a total volume of 80 L of a base solution, the pH value of the mixed system was adjusted to 12.3-12.4, the ammonia content was 2-3 g / L, and the temperature was controlled at 55°C. The stirring device was started, and the stirring rate was 850 r / min. Nitrogen was continuously introduced into the liquid surface of the reaction kettle at a rate of 5 L / min. The above-prepared nickel-cobalt-manganese mixed salt solution, complexing agent solution and precipitant solution were added to the reaction kettle through three precision metering pumps to carry out the first-stage nucleation zone aluminum-free co-precipitation reaction, the pH value was controlled at 12.2-12.3, when the particle size grew to 1.7 μm, the precipitant solution stopped flowing, the fourth precision metering pump was started to continuously add the aluminum-alkali solution I into the reaction kettle, the pH value was controlled at 11.7-11.8, the flow rate of the nickel-cobalt-manganese mixed salt solution was 80 mL / min, and the flow rate of the aluminum-alkali solution I was 80.5 mL / min. The reaction temperature was 55°C, the ammonia content of the mixed system was 2-3 g / L, the stirring rate was 850 rpm, and the reaction was stopped when the particle size grew to 4 μm. The reaction slurry obtained by the reaction was subjected to solid-liquid separation to obtain a dehydrated precursor slurry; Step S3: the dehydrated precursor slurry was put into the reaction kettle, the material-water ratio was controlled at 2:3, the aluminum-alkali solution I was pumped into the reaction kettle through a precision metering pump, the flow rate of the aluminum-alkali solution I was 50.2 mL / min, and this stage was the aluminum coating layer formation stage. The pH value of the mixed system in the reaction kettle was 9.5-9.7, the reaction temperature was 50°C, and the stirring rate was 450 rpm during the whole reaction process. The coated material was washed with water, and the dehydrated material was obtained after solid-liquid separation. The Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2precursor was obtained by drying at 110°C.

[0033] Comparative Example 4 (constant addition of high concentration aluminum-alkali solution) Step S1: prepare a mixed nickel-cobalt-manganese salt solution with a total metal concentration of 1.8 mol / L by using nickel sulfate, cobalt sulfate and manganese sulfate, wherein the molar ratio of nickel, cobalt and manganese is 93.88:4.08:2.04; add sodium metaaluminate into a prepared 4 mol / L sodium hydroxide solution to form a mixed sodium metaaluminate and sodium hydroxide solution, and the specific preparation process is to add 7.5 g of sodium metaaluminate into 1 L of 4 mol / L sodium hydroxide solution to prepare an aluminum-alkali solution II with a concentration of 0.09 mol / L; prepare an ammonia solution with a concentration of 6 mol / L as a complexing agent solution, and prepare a 4 mol / L sodium hydroxide solution as a precipitant solution; Step S2: add 78.6 L of pure water, 1.2 L of the complexing agent solution and 0.2 L of the precipitant solution into a reaction kettle to prepare a bottom liquid with a total volume of 80 L, adjust the pH value of the mixed system to 12.3-12.4, the ammonia content to 2-3 g / L, and the temperature to 55°C. Start the stirring device at a stirring rate of 850 r / min, and continuously introduce nitrogen into the liquid surface of the reaction kettle at a rate of 5 L / min. Add the prepared mixed nickel-cobalt-manganese salt solution, the complexing agent solution and the precipitant solution into the reaction kettle through three precision metering pumps to perform a first-stage nucleation zone aluminum-free co-precipitation reaction, the pH value is controlled to be 12.2-12.3, when the particle size grows to 1.7 μm, the introduction of the precipitant solution is stopped, the fourth precision metering pump is started to continuously add the aluminum-alkali solution II into the reaction kettle, the pH value is controlled to be 11.7-11.8, the flow rate of the mixed nickel-cobalt-manganese salt solution is 80 mL / min, and the flow rate of the aluminum-alkali solution II is 40.2 mL / min. The reaction temperature is 55°C, the ammonia content of the mixed system is 2-3 g / L, the stirring rate is 850 rpm during the whole reaction process, and the reaction is stopped when the particle size grows to 4 μm. The reaction slurry obtained in the reaction is subjected to solid-liquid separation to obtain a dehydrated precursor slurry; Step S3: put the dehydrated precursor slurry into a reaction kettle, control the material-water ratio to be 2:3, and add the aluminum-alkali solution II into the reaction kettle through a precision metering pump, the flow rate of the aluminum-alkali solution II is 14.8 mL / min, this stage is an aluminum coating layer forming stage, the pH value of the mixed system in the reaction kettle is 9.5-9.7, the reaction temperature is 50°C, and the stirring rate is 450 rpm during the whole reaction process. The coated material is washed with water, subjected to solid-liquid separation to obtain a dehydrated material, and then dried at 110°C to obtain a Ni 0.92 Co 0.04 Mn 0.02 Al 0.02 (OH)2 precursor.

[0034] Figure 4The discharge cycle and capacity comparison curve of the lithium ion battery assembled by the positive electrode material prepared by sintering the precursor prepared in Example 1 and Comparative Examples 1-2 are shown in the figure, and it can be seen from the figure that the process comparison of the gradient aluminum coating of Example 1, the aluminum doping of Comparative Example 1 and the aluminum coating of Comparative Example 2, the cycle reversibility and the discharge specific capacity of the lithium ion battery assembled by the positive electrode material prepared by sintering the precursor prepared in the application are greatly improved.

[0035] Figure 5 The discharge cycle and capacity comparison curve of the lithium ion battery assembled by the positive electrode material prepared by sintering the precursor prepared in Example 1 and Comparative Examples 3-4 are shown in the figure, and it can be seen from the figure that the process comparison of the step-by-step increasing concentration gradient aluminum coating of Example 1, the constant low concentration gradient aluminum coating of Comparative Example 3 and the constant high concentration gradient aluminum coating of Comparative Example 4, the cycle reversibility of the lithium ion battery assembled by the positive electrode material prepared by sintering the precursor prepared in the application is greatly improved.

[0036] The above examples describe the basic principles, main features and advantages of the application, and those skilled in the art should understand that the application is not limited by the above examples, and the above examples and descriptions in the specification are only to illustrate the principles of the application, and various changes and improvements can be made without departing from the scope of the application, and these changes and improvements all fall within the scope of the application.

Claims

1. A method for preparing a lithium-ion battery cathode material precursor with modified gradient aluminum coating, characterized in that... The specific preparation steps are as follows: Step S1: Prepare a nickel-cobalt-manganese mixed salt solution, a complexing agent solution, and a precipitant solution respectively. Dissolve an aluminum salt in an excess of alkaline solution to prepare an aluminum-alkali solution. The aluminum salt is one or more of aluminum sulfate, sodium aluminate, and aluminum nitrate. The alkaline solution is a sodium hydroxide solution or a potassium hydroxide solution. Step S2: A mixed solution of precipitant solution, complexing agent solution, and pure water is added to the reactor and a protective gas is continuously introduced. Then, a nickel-cobalt-manganese mixed salt solution, precipitant solution, and complexing agent solution are injected into the reactor through precision metering pumps for co-deposition reaction. When the particle size grows to 1.5~2μm, the precipitant solution injection is stopped, and an aluminum-alkali solution is injected into the reactor through a precision metering pump. This stage is the aluminum-free crystal nucleation zone. When the particle size grows to 2.5~4μm, the injection flow rate of the aluminum-alkali solution is increased gradually until the particle size grows to the target size, and the reaction is stopped. This stage is the aluminum gradient doped crystal growth zone. The reaction slurry obtained from the reaction is subjected to solid-liquid separation to obtain a dehydrated precursor slurry. Step S3: The dehydrated precursor slurry is put into the reactor, and the material-to-water ratio is controlled at 2:

3. The aluminum-alkali solution is pumped into the reactor through a precision metering pump. This stage is the aluminum coating layer formation stage. After the coating is completed, the material is washed with water and then dehydrated after solid-liquid separation. The material is then dried at 100~150℃ to obtain the modified gradient coated aluminum lithium-ion battery cathode material precursor.

2. The method for preparing the modified gradient-coated aluminum lithium-ion battery cathode material precursor according to claim 1, characterized in that... The specific preparation steps are as follows: Step S1: Prepare a nickel-cobalt-manganese mixed salt solution, a complexing agent solution, and a precipitant solution respectively. Dissolve aluminum salt in excess alkaline solution to prepare aluminum-alkali solution I and aluminum-alkali solution II of different concentrations respectively. The aluminum salt is one or more of aluminum sulfate, sodium aluminate, and aluminum nitrate, and the alkaline solution is sodium hydroxide solution or potassium hydroxide solution. Step S2: A mixed solution of precipitant solution, complexing agent solution, and pure water is added to the reactor, and a protective gas is continuously introduced. Then, a nickel-cobalt-manganese mixed salt solution, precipitant solution, and complexing agent solution are separately injected into the reactor via precision metering pumps for co-deposition. When the particle size grows to 1.5~2 μm, the precipitant solution injection is stopped, and aluminum-alkali solution I is injected into the reactor via a precision metering pump. This stage is the aluminum-free crystal nucleation zone. When the particle size grows to 2.5~4 μm, aluminum-alkali solution II is injected into the reactor via a precision metering pump. Inside the container, the concentration of aluminum-alkali solution II is greater than that of aluminum-alkali solution I, and the flow ratio of aluminum-alkali solution II to aluminum-alkali solution I is 1:2~4. The reaction continues until the particle size grows to the target particle size, at which point the reaction stops. This stage is the crystal growth region for aluminum gradient doping. Throughout the reaction, the temperature of the reactor is 30~80℃, the pH of the mixed system inside the reactor is 9~13, the concentration of the complexing agent inside the reactor is 1~20g / L, and the stirring rate is 200~1000rpm. The reaction slurry obtained from the reaction is then subjected to solid-liquid separation to obtain a dehydrated precursor slurry. Step S3: The dehydrated precursor slurry is added to the reactor, and the material-to-water ratio is controlled at 2:

3. The aluminum-alkali solution I is separately pumped into the reactor through a precision metering pump. This stage is the aluminum coating layer formation stage. During the entire reaction process, the pH of the mixed system in the reactor is 9~11, the reaction temperature is 40~60℃, and the stirring speed is 200~500rpm. After the coating is completed, the material is washed with water and dehydrated after solid-liquid separation. Then, it is dried at 100~150℃ to obtain the modified gradient-coated aluminum lithium-ion battery cathode material precursor.

3. The method for preparing the modified gradient-coated aluminum lithium-ion battery cathode material precursor according to claim 1 or 2, characterized in that: The total metal concentration of the nickel-cobalt-manganese mixed salt solution in step S1 is 1.5~2.5 mol / L. The nickel-cobalt-manganese mixed salt solution is composed of soluble nickel salt, soluble cobalt salt and soluble manganese salt and water. The complexing agent solution is an ammonia solution with a concentration of 1~10 mol / L. The precipitant solution is a sodium hydroxide solution or potassium hydroxide solution with a concentration of 1~8 mol / L.

4. The method for preparing the modified gradient-coated aluminum lithium-ion battery cathode material precursor according to claim 1 or 2, characterized in that: In step S2, the concentration of aluminum-alkali solution I is 0.02~0.04 mol / L, and the concentration of aluminum-alkali solution II is 0.08~0.10 mol / L.

5. The method for preparing the modified gradient-coated aluminum lithium-ion battery cathode material precursor according to claim 1 or 2, characterized in that: In step S2, aluminum-alkali solution I is an aluminum-alkali solution with a concentration of 0.03 mol / L obtained by adding 2.5 g of sodium aluminate to 1 L of 4 mol / L sodium hydroxide solution; aluminum-alkali solution II is an aluminum-alkali solution with a concentration of 0.09 mol / L obtained by adding 7.5 g of sodium aluminate to 1 L of 4 mol / L sodium hydroxide solution; the flow rate ratio of aluminum-alkali solution II to aluminum-alkali solution I is 1:

3.

6. The method for preparing the modified gradient-coated aluminum lithium-ion battery cathode material precursor according to claim 1 or 2, characterized in that: The molecular formula of the modified gradient-coated aluminum lithium-ion battery cathode material precursor mentioned in step S3 is Ni. X Co Y Mn 1-X-Y-Z Al Z (OH)2, of which 0.5 <X<1,0.01<Y<0.2,0.01≤Z<0.05,X+Y+Z<1。

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