A method for wet coating alumina on lithium ion battery positive electrode material

Abstract

The present invention belongs to the technical field of secondary battery materials and more specifically relates to a method for wet-coating alumina on a lithium-ion battery cathode material. The specific coating method of the present invention includes: dispersing a nickel cobalt lithium manganate positive electrode material in a dopamine solution with a concentration of 1.2-1.5 g / L, adjusting the pH to 7.5-8.0, stirring for reaction, filtering, washing and drying to obtain a pretreated nickel cobalt lithium manganate positive electrode material; taking 30-40 parts of the pretreated nickel cobalt lithium manganate positive electrode material, 300-400 parts of anhydrous ethanol, 30-40 parts of stearic acid, and 10-15 parts of aluminum isopropoxide by weight; dispersing the pretreated nickel cobalt lithium manganate positive electrode material in anhydrous ethanol, adding stearic acid and aluminum isopropoxide, then heating and reflux at a temperature of 75-80° C. for a reaction of 5.5-6.0 hours, discharging to obtain a precursor; and heating and calcining the precursor at a temperature of 400-450° C., cooling, and discharging to obtain a coated positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary battery materials and more specifically relates to a method for wet-coating alumina on a lithium-ion battery cathode material. Background Art

[0002] Lithium-ion battery cathode materials are coated with alumina to improve their electrochemical performance, thermal stability, and cycle life. On the one hand, since cathode materials are prone to side reactions with the electrolyte at high voltages, resulting in increased interfacial impedance and capacity decay, alumina, as an inert coating, can physically isolate the cathode material and the electrolyte, reducing the occurrence of side reactions. On the other hand, the cathode material undergoes volume changes and phase transitions (such as the transition from a layered structure to a spinel structure) during the charge and discharge process. Alumina coating can inhibit lattice distortion and maintain structural stability. Furthermore, volume changes during charge and discharge can easily lead to fracture of the cathode particles. The mechanical strength of alumina can inhibit crack propagation and extend the life of the material. Furthermore, after alumina coating, some aluminum ions may penetrate into the surface lattice of the cathode, forming a stable structure (such as LiAlO2), which increases the diffusion rate of lithium ions.

[0003] When wet-coating alumina layers on ternary cathode materials, the resulting alumina is likely primarily physically adsorbed, resulting in weak chemical bonding with the cathode material surface. This can lead to detachment from the cathode material during battery processing and during cyclic charge and discharge, thus impacting the battery's cycle life. Therefore, improving the bonding strength between the coating layer and the ternary cathode material remains a key challenge for those skilled in the art. Summary of the Invention

[0004] The technical problem to be solved by the present invention is that when lithium nickel cobalt manganese oxide cathode materials are wet-coated with alumina, the bonding strength between the alumina and the cathode material surface is weak, resulting in the alumina easily falling off the cathode material surface during battery processing, such as slurry mixing and coating, or during battery charge and discharge cycles, thereby affecting the battery's cycle life. The present invention provides a method for wet-coating alumina with lithium-ion battery cathode materials.

[0005] The purpose of the present invention is to provide a method for wet coating aluminum oxide on a lithium ion battery positive electrode material.

[0006] The above-mentioned purpose of the present invention is achieved through the following technical solutions:

[0007] A method for wet coating alumina on a lithium-ion battery cathode material, the specific coating method comprising:

[0008] By weight, take 30-40 parts of lithium nickel cobalt manganese oxide positive electrode material, 300-400 parts of anhydrous ethanol, 30-40 parts of stearic acid, and 10-15 parts of aluminum isopropoxide;

[0009] Wherein, the sphericity of the lithium nickel cobalt manganese oxide positive electrode material is 0.85-0.92;

[0010] The D50 of the lithium nickel cobalt manganese oxide positive electrode material is 5-12 μm;

[0011] The lithium nickel cobalt manganate cathode material is dispersed in anhydrous ethanol, and then stearic acid and aluminum isopropoxide are added, followed by heating under reflux at a temperature of 75-80°C for 5.5-6.0 hours, and the material is discharged to obtain a precursor;

[0012] The precursor is heated and calcined at a temperature of 400-450° C., cooled, and discharged to obtain the coated positive electrode material.

[0013] The beneficial effects of the above technical solution are:

[0014] The above technical solution uses a lithium nickel cobalt manganese oxide positive electrode material with a certain specification of sphericity and particle size as a matrix. The closer the sphericity is to 1, the closer the particle is to a theoretically perfect sphere. The higher the sphericity, the easier it is to form a uniform coating on the coating layer deposited on its surface during liquid phase deposition. Therefore, on this basis, it can tend to form a more uniform aluminum oxide coating layer. However, the inventors found that if the deposition rate of aluminum oxide or its precursor is too fast during the deposition process on a uniform spherical surface, it will also lead to uneven local deposition and even agglomeration problems. Based on this, the above technical solution of the present invention uses aluminum isopropoxide as the source of aluminum element, constructs a dehydration reaction system with anhydrous ethanol and stearic acid, and heats it under corresponding temperature conditions. During the hot reflux reaction, the hydroxyl groups in the anhydrous ethanol molecular structure can undergo dehydration condensation with the carboxyl groups in the stearic acid molecular structure to form ester groups. After the water molecules are generated, they can interact with the aluminum isopropoxide molecules, thereby hydrolyzing the aluminum isopropoxide molecules to generate a precursor. Once the precursor crystals are formed, they can be adsorbed on the surface of the lithium nickel cobalt manganese oxide positive electrode material. Since the aforementioned reaction between the anhydrous ethanol and stearic acid molecules is an organic dehydration condensation reaction, the aluminum isopropoxide plays the role of a dehydrating agent in this process, causing the chemical equilibrium of the dehydration condensation reaction to move to the right. In this way, the generation of water molecules during the reaction is slowly generated at the molecular level. Therefore, the subsequent precursor generation process is uniform and controllable, so that a uniform coating layer can be formed on the surface of the spherical substrate.

[0015] Furthermore, the specific coating method also includes:

[0016] The lithium nickel cobalt manganese oxide positive electrode material is dispersed in anhydrous ethanol, and then stearic acid and aluminum isopropoxide, as well as 8-12% glycerol by mass of anhydrous ethanol, are added. Then, the mixture is heated under reflux at a temperature of 75-80°C for 5.5-6.0 hours, and the material is discharged to obtain a precursor.

[0017] The beneficial effects of the above technical solution are:

[0018] By further adding a certain mass of glycerol to the reaction system, since the viscosity of glycerol is higher than that of anhydrous ethanol, after the addition of glycerol, the viscosity of the reaction system can be adjusted so that the viscosity is appropriately increased. Thus, the deposition rate during the coating process can be controlled to make the coating layer more uniform.

[0019] Furthermore, the specific coating method also includes:

[0020] The lithium nickel cobalt manganese oxide positive electrode material is dispersed in a dopamine solution with a concentration of 1.2-1.5 g / L, the pH is adjusted to 7.5-8.0, the mixture is stirred for reaction, and the mixture is filtered, washed and dried to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material;

[0021] By weight, take 30-40 parts of pretreated nickel cobalt lithium manganese oxide positive electrode material, 300-400 parts of anhydrous ethanol, 30-40 parts of stearic acid, and 10-15 parts of aluminum isopropoxide;

[0022] The pretreated lithium nickel cobalt manganese oxide cathode material is dispersed in anhydrous ethanol, and then stearic acid and aluminum isopropoxide are added, followed by heating under reflux at a temperature of 75-80°C for 5.5-6.0 hours, and the material is discharged to obtain a precursor;

[0023] The precursor is heated and calcined at a temperature of 400-450° C., cooled, and discharged to obtain the coated positive electrode material.

[0024] The beneficial effects of the above technical solution are:

[0025] The above technical solution further introduces dopamine into the reaction system, and utilizes the fact that in an alkaline environment, during the stirring process, dopamine undergoes oxidative self-polymerization under the action of dissolved oxygen in the reaction system, thereby improving the adsorption strength of the lithium nickel cobalt manganese oxide positive electrode material for the precursor produced by the hydrolysis of aluminum isopropoxide, thereby avoiding the shedding of the precursor during the preparation process or the shedding of the alumina coating during use; more importantly, since the dopamine molecular structure contains C and N elements, the coating layer exists at the interface between the alumina coating layer and the positive electrode material, and can also play a role in improving the interface ionic conductivity and electronic conductivity, which is beneficial to avoid the surface coating layer structure being unstable and shedding caused by excessive interface impedance during rapid charging and discharging.

[0026] Furthermore, the dopamine solution further comprises gelatin in an amount of 0.3-0.5% by mass of the dopamine solution;

[0027] The isoelectric point of the gelatin is 7.0.

[0028] The beneficial effects of the above technical solution are:

[0029] The above technical solution further introduces gelatin with an isoelectric point of 7.0 on the basis of dopamine. In the process of adjusting the pH to 7.5-8.0, since the pH of the system deviates from the isoelectric point of gelatin, the carboxyl groups in the molecular structure of gelatin are ionized. As a result, due to the same negative charge, the molecular chains of the gelatin molecules are fully stretched, and cooperate with dopamine to form a loose and continuous coating layer on the surface of the positive electrode material. In the subsequent heating and calcination process, a transition layer with rich porosity is formed, thereby improving the mass transfer capacity at the interface and facilitating the infiltration of the electrolyte.

[0030] Furthermore, the dopamine solution further comprises a non-ionic surfactant in an amount of 0.02-0.05% by mass of the dopamine solution;

[0031] The nonionic surfactant is selected from any one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyoxyethylene sorbitan ester, and coconut fatty acid diethylamide.

[0032] Furthermore, the specific coating method also includes:

[0033] Heat to 300-320℃ at a heating rate of 3-5℃ / min, keep warm and calcine for 30-40min,

[0034] Continue heating at a rate of 0.3-0.5°C / min to 400-450°C, keep warm and calcine for 45-60 minutes, cool naturally to room temperature, and discharge the material to obtain the coated positive electrode material.

[0035] Furthermore, the chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where 0.3<x<0.95, 0<y<1. DETAILED DESCRIPTION

[0036] The present invention is further described below with reference to specific examples, which, however, are not intended to limit the present invention in any way. Unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the art.

[0037] Unless otherwise specified, the reagents and materials used in the following examples were commercially available. Example 1

[0038] The lithium nickel cobalt manganese oxide positive electrode material and the dopamine solution with a concentration of 1.2 g / L were mixed in a mass ratio of 1:8, and ultrasonic dispersion was performed at an ultrasonic frequency of 55 kHz for 20 minutes. The pH was then adjusted to 7.5, and the mixture was stirred at a constant temperature of 55°C and a stirring speed of 400 r / min for 30 minutes. The mixture was filtered, the filter cake was collected, and the filter cake was washed with deionized water three times. The washed filter cake was then transferred to an oven and dried at a temperature of 95°C to constant weight to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material.

[0039] The chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where x=0.5, y=0.2;

[0040] The dopamine solution further comprises 0.3% gelatin by weight of the dopamine solution and 0.02% nonionic surfactant by weight of the dopamine solution; and the isoelectric point of the gelatin is 7.0;

[0041] The nonionic surfactant is selected from fatty alcohol polyoxyethylene ether;

[0042] By weight, take 30 parts of pretreated nickel cobalt lithium manganese oxide positive electrode material, 300 parts of anhydrous ethanol, 30 parts of stearic acid, and 10 parts of aluminum isopropoxide;

[0043] The pretreated lithium nickel cobalt manganese oxide cathode material was mixed with anhydrous ethanol, and ultrasonically dispersed for 20 minutes at an ultrasonic frequency of 55 kHz. Stearic acid, aluminum isopropoxide, and glycerol (8% by weight of anhydrous ethanol) were then added. The mixture was then heated under reflux at 75°C for 5.5 hours and discharged to obtain a precursor.

[0044] The precursor was transferred into a muffle furnace and heated to 300°C at a heating rate of 3°C / min. After calcining for 30 minutes, it was heated to 400°C at a rate of 0.3°C / min. After calcining for 45 minutes, it was naturally cooled to room temperature and discharged to obtain the coated positive electrode material. Example 2

[0045] The lithium nickel cobalt manganese oxide positive electrode material and the dopamine solution with a concentration of 1.3 g / L were mixed in a mass ratio of 1:9, and ultrasonic dispersion was performed at an ultrasonic frequency of 60 kHz for 25 minutes. The pH was then adjusted to 7.8, and the mixture was stirred at a constant temperature of 60°C and a stirring speed of 500 r / min for 35 minutes. The mixture was filtered, the filter cake was collected, and the filter cake was washed with deionized water 4 times. The washed filter cake was then transferred to an oven and dried at a temperature of 98°C to constant weight to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material.

[0046] The chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where x=0.5, y=0.2;

[0047] The dopamine solution further comprises 0.4% gelatin by weight of the dopamine solution and 0.03% nonionic surfactant by weight of the dopamine solution; and the isoelectric point of the gelatin is 7.0;

[0048] The nonionic surfactant is selected from alkylphenol polyoxyethylene ether;

[0049] By weight, 35 parts of pretreated nickel cobalt lithium manganese oxide positive electrode material, 350 parts of anhydrous ethanol, 35 parts of stearic acid, and 12 parts of aluminum isopropoxide were taken;

[0050] The pretreated lithium nickel cobalt manganese oxide cathode material was mixed with anhydrous ethanol, and ultrasonically dispersed for 26 minutes at an ultrasonic frequency of 60 kHz. Stearic acid, aluminum isopropoxide, and glycerol (10% by weight of anhydrous ethanol) were then added. The mixture was then heated under reflux at 78°C for 5.8 hours and discharged to obtain a precursor.

[0051] The precursor was transferred into a muffle furnace and heated to 310°C at a heating rate of 4°C / min. After calcination for 35 minutes, the precursor was heated to 420°C at a rate of 0.4°C / min. After calcination for 50 minutes, the precursor was naturally cooled to room temperature and discharged to obtain the coated positive electrode material. Example 3

[0052] The lithium nickel cobalt manganese oxide positive electrode material and the dopamine solution with a concentration of 1.5 g / L were mixed in a mass ratio of 1:10, and ultrasonic dispersion was performed at an ultrasonic frequency of 65 kHz for 30 minutes. The pH was then adjusted to 8.0, and the mixture was stirred at a constant temperature of 65°C and a stirring speed of 600 r / min for 40 minutes. The mixture was filtered, the filter cake was collected, and the filter cake was washed with deionized water 5 times. The washed filter cake was then transferred to an oven and dried at a temperature of 100°C to constant weight to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material.

[0053] The chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where x=0.6, y=0.2;

[0054] The dopamine solution further comprises 0.5% gelatin by weight of the dopamine solution and 0.05% nonionic surfactant by weight of the dopamine solution; and the isoelectric point of the gelatin is 7.0;

[0055] The nonionic surfactant is selected from polyoxyethylene sorbitan ester;

[0056] By weight, take 40 parts of pretreated nickel cobalt lithium manganese oxide positive electrode material, 400 parts of anhydrous ethanol, 40 parts of stearic acid, and 15 parts of aluminum isopropoxide;

[0057] The pretreated lithium nickel cobalt manganese oxide cathode material was mixed with anhydrous ethanol and ultrasonically dispersed for 30 minutes at an ultrasonic frequency of 65kHz. Stearic acid, aluminum isopropoxide, and glycerol (12% by weight of anhydrous ethanol) were then added.

[0058] Then, the mixture was heated under reflux at 80°C for 6.0 h, and the precursor was obtained after discharging.

[0059] The precursor was transferred into a muffle furnace and heated to 320°C at a heating rate of 5°C / min. After calcining for 40 minutes, it was further heated to 450°C at a rate of 0.5°C / min. After calcining for 60 minutes, it was naturally cooled to room temperature and discharged to obtain the coated positive electrode material. Example 4

[0060] Compared with Example 1, this embodiment differs in that gelatin is not added, and other conditions remain unchanged. Example 5

[0061] Compared with Example 1, this example differs in that the isoelectric point of gelatin is 7.5, and the other conditions remain unchanged. Example 6

[0062] Compared with Example 1, this embodiment differs in that no nonionic surfactant is added, and other conditions remain unchanged. Example 7

[0063] The difference between this embodiment and embodiment 1 is that deionized water of equal mass is used to replace the dopamine solution, and other conditions remain unchanged.

[0064] Comparative Example 1

[0065] Compared with Example 1, this comparative example has the following differences:

[0066] The lithium nickel cobalt manganese oxide positive electrode material and the dopamine solution with a concentration of 1.2 g / L were mixed in a mass ratio of 1:8, and ultrasonic dispersion was performed at an ultrasonic frequency of 55 kHz for 20 minutes. The pH was then adjusted to 7.5, and the mixture was stirred at a constant temperature of 55°C and a stirring speed of 400 r / min for 30 minutes. The mixture was filtered, the filter cake was collected, and the filter cake was washed with deionized water three times. The washed filter cake was then transferred to an oven and dried at a temperature of 95°C to constant weight to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material.

[0067] The chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where x=0.5, y=0.2;

[0068] The dopamine solution further comprises 0.3% gelatin by weight of the dopamine solution and 0.02% nonionic surfactant by weight of the dopamine solution; and the isoelectric point of the gelatin is 7.0;

[0069] The nonionic surfactant is selected from fatty alcohol polyoxyethylene ether;

[0070] By weight, 30 parts of pretreated lithium nickel cobalt manganese oxide positive electrode material, 300 parts of anhydrous ethanol, 10 parts of deionized water, and 10 parts of aluminum isopropoxide were taken;

[0071] The pretreated lithium nickel cobalt manganese oxide cathode material and anhydrous ethanol were mixed and ultrasonically dispersed for 20 minutes at an ultrasonic frequency of 55 kHz. Aluminum isopropoxide and glycerol (8% by weight of anhydrous ethanol) were then added. Subsequently, deionized water was added dropwise at a rate of 5 mL / min while stirring at a temperature of 75°C and a stirring speed of 200 r / min. After the addition of deionized water was completed, the mixture was heated and stirred for 2 hours before discharging to obtain a precursor.

[0072] The precursor was transferred into a muffle furnace and heated to 300°C at a heating rate of 3°C / min. After calcining for 30 minutes, it was heated to 400°C at a rate of 0.3°C / min. After calcining for 45 minutes, it was naturally cooled to room temperature and discharged to obtain the coated positive electrode material.

[0073] The performance tests of the products obtained in the above examples and comparative examples were carried out, and the specific test methods and test results are as follows:

[0074] The coated positive electrode material, binder PVDF, and conductive agent acetylene black obtained in the embodiment and comparative example were mixed at a mass ratio of 96:2:2. Specifically, the binder PVDF and the solvent NMP were first mixed and stirred thoroughly to obtain a glue solution, and then acetylene black and the positive electrode material were added. After stirring evenly, the mixture was coated on the surface of the aluminum foil. The coated positive electrode sheet was dried, cold pressed, and cut to adjust the thickness of the active material layer on the aluminum foil to 80 μm and the compaction density to 3.6 g / cm 3 ;

[0075] Assemble the positive electrode shell, positive electrode sheet, electrolyte, diaphragm, electrolyte, lithium sheet, gasket, spring, and negative electrode shell in the order of CR2032 button battery in a vacuum glove box, and finally press it with a sealing machine, let it stand for 24 hours, and test its electrochemical performance;

[0076] Among them, the diaphragm is Celgard2400 polypropylene microporous diaphragm, the lithium salt in the electrolyte is lithium hexafluorophosphate (concentration is 1 mol / L), and the solvent is a mixture of EC:DMC:DEC=1:1:1.

[0077] The assembled button battery was charged and discharged at a constant current using a Blue Electric test system (CT2001A) with a voltage window of 3.0-4.5V at a constant temperature of 25°C. The test yielded a capacity retention rate after 450 cycles at 0.1C. The detailed test results are shown in Table 1.

[0078] Table 1: Product performance test results

[0079] ;

[0080] ;

[0081] It can be seen from the test results in Table 1 that the product obtained by the present invention can be used in batteries to significantly improve the cycle life of the product.

[0082] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be considered as equivalent replacement methods and are included in the scope of protection of the present invention.

Claims

1. A method for wet coating alumina on a lithium ion battery cathode material, characterized in that: Specific coating methods include: The lithium nickel cobalt manganese oxide positive electrode material is dispersed in a dopamine solution with a concentration of 1.2-1.5 g / L, the pH is adjusted to 7.5-8.0, the mixture is stirred for reaction, and the mixture is filtered, washed and dried to obtain a pretreated lithium nickel cobalt manganese oxide positive electrode material; The dopamine solution comprises gelatin in an amount of 0.3-0.5% by mass of the dopamine solution; The isoelectric point of the gelatin is 7.0; By weight, take 30-40 parts of pretreated nickel cobalt lithium manganese oxide positive electrode material, 300-400 parts of anhydrous ethanol, 30-40 parts of stearic acid, and 10-15 parts of aluminum isopropoxide; Wherein, the sphericity of the lithium nickel cobalt manganese oxide positive electrode material is 0.85-0.92; The D50 of the lithium nickel cobalt manganese oxide positive electrode material is 5-12 μm; The pretreated lithium nickel cobalt manganese oxide cathode material is dispersed in anhydrous ethanol, and then stearic acid and aluminum isopropoxide are added, followed by heating under reflux at a temperature of 75-80°C for 5.5-6.0 hours, and the material is discharged to obtain a precursor; The precursor is heated and calcined at a temperature of 400-450° C., cooled, and discharged to obtain the coated positive electrode material.

2. The method for wet coating alumina on a lithium ion battery cathode material according to claim 1, characterized in that: The specific coating method also includes: The lithium nickel cobalt manganese oxide positive electrode material is dispersed in anhydrous ethanol, and then stearic acid and aluminum isopropoxide, as well as 8-12% glycerol by mass of anhydrous ethanol, are added. Then, the mixture is heated under reflux at a temperature of 75-80°C for 5.5-6.0 hours, and the material is discharged to obtain a precursor.

3. The method for wet coating alumina on a lithium ion battery cathode material according to claim 1, characterized in that: The dopamine solution further comprises a nonionic surfactant in an amount of 0.02-0.05% by mass of the dopamine solution; The nonionic surfactant is selected from any one of fatty alcohol polyoxyethylene ether, alkylphenol polyoxyethylene ether, polyoxyethylene sorbitan ester, and coconut fatty acid diethylamide.

4. The method for wet coating alumina on a lithium ion battery cathode material according to claim 1, characterized in that: The specific coating method also includes: The temperature is raised to 300-320°C at a heating rate of 3-5°C / min, and the temperature is kept at this temperature for 30-40 minutes. The temperature is then raised to 400-450°C at a heating rate of 0.3-0.5°C / min, and the temperature is kept at this temperature for 45-60 minutes. The material is then naturally cooled to room temperature and discharged to obtain the coated positive electrode material.

5. The method for wet coating alumina on a lithium ion battery cathode material according to claim 1, characterized in that: The chemical formula of the lithium nickel cobalt manganese oxide positive electrode material is LiNi x Co y Mn 1-x-y O2, where 0.3<x<0.95, 0<y<1.