A multi-layer coated positive electrode material and a method for preparing the same

Abstract

The present application relates to a kind of multilayer coated positive electrode materials and its preparation method.The first coating layer of the multilayer coated positive electrode material is evenly coated on the surface of material, the coating layer can control the element diffusion between matrix and second coating layer by evenly coating and regulating thickness, to form specific surface doping coating structure.Second coating layer is coated on the surface of first coating layer, the coating layer can avoid competition reaction between elements by the form of doped hydroxide, which is beneficial to the control of surface morphology and improve coating uniformity.The double-layer coating design can significantly improve the lithium ion transport performance and element elution stability of lithium ion battery positive electrode material.In addition, the process of the present application is simple, easy to realize industrial production.

Description

TECHNICAL FIELD

[0001] The application relates to a multi-layer coated positive electrode material and a preparation method thereof, and belongs to the field of lithium ion battery electrode materials. BACKGROUND

[0002] The application cut-off voltage of the positive electrode material for consumer electronics is getting higher and higher, and has been developed to 4.50V and 4.53V, and a lithium cobaltate field for power is also derived. Under the current voltage and future higher application voltage system and power application system, the control of material surface modification needs to be more refined. Co additive is generally used for surface modification modification to control the surface residual lithium content and improve the electrochemical performance such as cycle and storage. During this period, there are also preparation of doped Co coating additives, such as the related patent "4.45V or above lithium ion battery lithium cobaltate positive electrode material and preparation method thereof" (patent application number: 201811215476.1) reports that Y, Ti, Sn, Mn and other doped elements are doped with CoCO3 to coat and improve the high-voltage performance of lithium cobaltate.

[0003] However, although the above patent prepares a doped Co additive material, it is difficult to obtain a nano-sized surface coating additive under the CoCO3 system, and the nanocrystallization of the surface coating substance is crucial for the uniformity control and electrochemical performance improvement of the coating. At the same time, the above patent lacks Al and Ni elements which have an important influence on the electrochemical performance of the positive electrode material. SUMMARY

[0004] The application aims to provide a multi-layer coated positive electrode material and a preparation method thereof. The first coating layer is uniformly coated on the surface of the material. The coating layer can control the element diffusion between the substrate and the second coating layer by uniform coating and thickness regulation, so as to form a specific surface doping coating structure. The second coating layer is coated on the surface of the first coating layer. The second coating layer in the form of a doped hydroxide can avoid the competition reaction between elements, which is beneficial to the control of the surface morphology and the improvement of the coating uniformity.

[0005] To achieve the above-mentioned purpose, the application adopts the following technical scheme:

[0006] A multi-layer coated positive electrode material, the structural formula of the multi-layer coated positive electrode material is LizMAO2, M=Ni 1-x- y Mn x Co y , 0 y ≤1, 1 z ≤1.2, M is at least one of transition metals Ni, Co and Mn, and the modified element A (i.e. coating element) is at least one of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn and Zn.

[0007] The multi-layer coated positive electrode material comprises a first coating layer and a second coating layer.

[0008] The first coating layer is uniformly coated on the surface of the base material (lithium cobaltate or other positive electrode material primary product), and the coating element is selected from at least one of Mg, Ti, Al, La, Y, and Zr.

[0009] The second coating layer is coated on the surface of the first coating layer, and the coating element is selected from one or more of Mg, Ti, Al, La, Y, Zr, Co, Ni, Mn, Ca, Sn, and Zn, and the coating element of the second coating layer at least contains one of Co, Ni, and Mn.

[0010] Further, the mass of the modification element A accounts for 0.01% to 1% of the total mass of the multi-layer coated positive electrode material.

[0011] Further, the first coating layer can be introduced by uniform coating of ALD (Atomic Layer Deposition), and the coating thickness is 0.05-50nm.

[0012] Further, the second coating layer is introduced in the form of doped hydroxide, which can avoid competition between elements, and is conducive to the control of surface morphology and the improvement of coating uniformity.

[0013] Further, the particle size of the doped hydroxide is controlled to be nanoscale, which is 10nm-900nm.

[0014] Further, the doped elements of the doped hydroxide, such as Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn, are introduced by precursor precipitation.

[0015] A preparation method of a multi-layer coated positive electrode material, comprising the following steps:

[0016] ALD coating is performed on the base material (lithium cobaltate or other positive electrode material primary product) to obtain a first coating layer.

[0017] Doped nanometer hydroxide is prepared.

[0018] The doped nanometer hydroxide is used as an additive to perform second coating on the base material with the first coating layer to obtain a double-layer coated positive electrode material.

[0019] The double-layer coated positive electrode material is sintered and crushed to obtain a final positive electrode material.

[0020] Further, the preparation of the doped nanometer hydroxide comprises:

[0021] (1) A certain amount of nickel-cobalt-manganese salt raw material is dissolved in water to obtain a nickel-cobalt-manganese salt solution; the nickel-cobalt-manganese salt contains at least one of Ni, Co, and Mn.

[0022] (2) A soluble salt raw material containing at least one of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn is added to the nickel-cobalt-manganese salt solution of step (1) according to a metering ratio to obtain a mixed salt solution.

[0023] (3) A precipitant solution of a certain concentration is prepared for standby.

[0024] (4) Pure water is added to a reactor as a bottom liquid, nitrogen is introduced as a protective atmosphere, stirring is started and maintained at a high rate. The mixed salt solution and the precipitant solution are simultaneously and concurrently introduced into the reactor after heating to a certain temperature, the reaction pH value is maintained at 10-13 during the process, and the precipitation reaction is performed for 5-10 h, then the rotation speed is reduced for crystallization for 2-4 h to obtain a slurry.

[0025] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing, sieving, and a doped nano-hydroxide is obtained.

[0026] Further, the metal salt (nickel-cobalt-manganese salt) in step (1) can be one of a sulfate salt, a chloride salt, a nitrate salt, and an acetate salt.

[0027] Further, the salt of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn in step (2) can be one of a water-soluble sulfate salt, a chloride salt, a nitrate salt, and an acetate salt.

[0028] Further, the precipitant in step (3) is one of sodium hydroxide, potassium hydroxide, and ammonia water, and the concentration of the precipitant is 0.5-4 mol / L.

[0029] Further, the reaction temperature in step (4) is 40-75°C, and the reaction pH value is controlled at 10-13.

[0030] Further, the crushing in step (5) is performed by a pulverizer, and the pulverizing time is 1-3 min.

[0031] Further, the mass ratio of the coating elements of the first coating layer and the second coating layer is 0.01%-0.5%.

[0032] Further, the coating element of the first coating layer is selected from at least one of Mg, Ti, Al, La, Y, and Zr, and the element introduction mode is a metal organic salt such as bis(ethylcyclopentadienyl)magnesium, titanium tetraisopropoxide, trimethylaluminum, tris(isopropylcyclopentadienyl) lanthanum, and tris(N,N'-diisopropylacetamidine) yttrium.

[0033] Further, the first coating layer, taking Al coating as an example, the ALD process is: first, trimethylaluminum vapor pulse into the reaction kettle, chemical adsorption occurs on the surface of the positive electrode material; second, the cleaning gas N2 removes the excess trimethylaluminum vapor and the reaction by-product methane from the reaction kettle which is not adsorbed on the surface of the positive electrode material; third, H2O vapor pulse into the reaction kettle, and the trimethylaluminum adsorbed on the surface of the positive electrode material reacts to form Al2O3; fourth, the cleaning gas N2 removes the excess H2O vapor and the by-product methane produced in the reaction from the reaction kettle. The specific reaction formula is as follows:

[0034] 2Al(CH3)3(g)+3H2O(g)→Al2O3(s)+6CH4(g)

[0035] Further, the double-layer coated positive electrode material is sintered, the sintering temperature is controlled at 500-1050 DEG C, the sintering time is controlled at 8-20 hours, and the crushing treatment is carried out after sintering.

[0036] Further, the above preparation method further comprises the step of performing the coin cell floating performance test on the prepared sample, and the test method is: the positive electrode material, carbon black and PVDF (polyvinylidene fluoride) are uniformly coated on the aluminum foil in a ratio of 90:5:5 to form a coin half cell with a lithium sheet negative electrode, the coin half cell is activated by charging and discharging at 0.2C for 1 week under normal temperature condition of 4.53V, and then the coin half cell is charged at 0.5C to 4.6V in a 60 DEG C oven, and the voltage is kept for 300 hours, and the current curve is observed to observe the lifting time.

[0037] The advantages of the present application are as follows:

[0038] 1. The multi-layer coated positive electrode material and the preparation method thereof use a double-layer coating design, the first coating layer is uniformly coated on the surface of the material in the form of ALD coating, etc., which can realize uniform coating and thickness control, and the second coating layer is coated in the form of a nano-scale doped hydroxide, the deposition of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, Zn on the surface of the precursor during the precipitation stage can effectively avoid the competition reaction between elements, which is conducive to the control of the surface morphology and the improvement of the coating uniformity. The introduction of Co, Ni, Mn, etc. has the functions of absorbing the residual lithium on the surface of the positive electrode material and improving the interface storage and safety, and the introduction of Mg, Ti, Al, La, Y, Zr, Ca, Sn, Zn is conducive to improving the lithium ion transmission rate on the surface of the positive electrode material, improving the lithium transmission kinetics, and solving the problems of cycle, storage, floating, etc. faced by the development of high-voltage materials.

[0039] 2. The operation process is simple, the raw material cost is low, and the industrialized production is easy to realize. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 This is the SEM (scanning electron microscope) image of the ALD coated sample.

[0041] Figure 2 La, Y doped Co of Example 12 0.8 Ni 0.2 SEM image of (OH)2(La0.1%, Y0.1%).

[0042] Figure 3 It is a comparison (TEM-EDS) diagram of Ni element doping depth between Example 6 and the comparative example.

[0043] Figure 4 1 to 15 correspond to Examples 1 to 15, and 16 corresponds to the corresponding ratio. DETAILED DESCRIPTION

[0044] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to specific embodiments and accompanying drawings.

[0045] Example 1

[0046] (1) Prepare 0.5 ml / L cobalt sulfate solution.

[0047] (2) Soluble magnesium sulfate is added to cobalt sulfate at a mass ratio of 0.005% of the Mg element to the lithium cobalt oxide positive electrode material to obtain a mixed salt solution.

[0048] (3) Prepare 0.5 ml / L NaOH solution for later use.

[0049] (4) Pure water was added to the reactor as the bottom liquid, nitrogen was introduced as a protective atmosphere, stirring was started and a high speed was maintained. The temperature was raised to 40°C, and the mixed salt solution and the precipitant solution were added to the reactor simultaneously and in parallel. The pH value of the reaction was maintained at 10 during the process. After the precipitation reaction for 5 hours, the speed was reduced and crystallization was carried out for 2 hours to obtain a slurry.

[0050] (5) The slurry is subjected to multiple hot water washing, solid-liquid separation, drying, crushing for 1 min, and sieving to obtain doped nano-hydroxide.

[0051] (6) ALD coating of Mg element is performed on primary positive electrode materials such as lithium cobalt oxide, wherein the mass ratio of Mg element in the lithium cobalt oxide positive electrode material is 0.005%. After the coating is completed, a first coating layer is obtained. Figure 1 is the SEM image of the ALD coated sample.

[0052] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat the lithium cobaltate positive electrode material obtained in step (6) with a second coating layer, wherein the mass ratio of Co element in the nano-hydroxide to the lithium cobaltate positive electrode material is 0.5%.

[0053] (8) The double-coated positive electrode material obtained in step (7) is sintered, the sintering temperature is controlled at 500°C, the sintering time is controlled at 8 hours, and after sintering, crushing treatment is performed.

[0054] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material, carbon black and PVDF are uniformly coated on an aluminum foil in a ratio of 90:5:5 to form a coin half cell with a lithium sheet negative electrode, and the coin half cell is activated by charging and discharging at 0.2C for 1 week at room temperature at 4.53V, and then the coin half cell is charged at 0.5C to 4.6V in a 60°C oven, and the voltage is kept constant for 300 hours, and the current curve is observed to determine the lifting time.

[0055] Example 2

[0056] (1) A 0.5ml / L cobalt sulfate solution is prepared.

[0057] (2) A soluble lanthanum sulfate is added to the cobalt sulfate solution in an amount of 0.005% of La element based on the mass of the lithium cobaltate positive electrode material to obtain a mixed salt solution.

[0058] (3) A 0.5ml / L NaOH solution is prepared for standby use.

[0059] (4) Pure water is added to a reactor as a base solution, nitrogen gas is introduced as a protective atmosphere, stirring is started and maintained at a high speed. The temperature is raised to 40°C, and the mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reactor, and the pH value of the reaction is maintained at 10 during the process. After 5h of precipitation reaction, the rotation speed is reduced for 2h of crystallization to obtain a slurry.

[0060] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 1min, and sieving to obtain a doped nano-hydroxide.

[0061] (6) The lithium cobaltate positive electrode material is subjected to ALD coating of La element, and the mass ratio of La element to the lithium cobaltate positive electrode material is 0.005%, and a first coating layer is obtained after coating.

[0062] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat the lithium cobaltate positive electrode material obtained in step (6) with a second coating layer, wherein the mass ratio of Co element in the nano-hydroxide to the lithium cobaltate positive electrode material is 0.5%.

[0063] (8) The double-layer coated positive electrode material obtained in step (7) is sintered, the sintering temperature is controlled at 500°C, the sintering time is controlled at 8 hours, and after sintering, crushing treatment is performed.

[0064] (9) The prepared sample is subjected to button cell floating performance test, the test method is as follows: the positive electrode material, carbon black and PVDF are uniformly coated on an aluminum foil in a ratio of 90:5:5 to form a button cell half-cell with a lithium sheet negative electrode, the button cell half-cell is activated by 0.2C charging and discharging at 4.53V under normal temperature conditions for 1 week, and then the button cell half-cell is charged to 4.6V at 0.5C in a 60°C oven, and the voltage is kept for 300 hours, and the current curve is observed to determine the lifting time.

[0065] Example 3

[0066] (1) A 0.5ml / L cobalt sulfate solution is prepared.

[0067] (2) A soluble yttrium sulfate is added to the cobalt sulfate to obtain a mixed salt solution, and the mass ratio of Y element to lithium cobalt oxide positive electrode material is 1.75%.

[0068] (3) A 0.5ml / L NaOH solution is prepared for standby use.

[0069] (4) Pure water is added to the reactor as a bottom liquid, nitrogen is introduced as a protective atmosphere, stirring is started and maintained at a high speed. The temperature is raised to 40°C, the mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reactor, and the pH value is maintained at 10 during the process. After 5h of precipitation reaction, the speed is reduced for crystallization for 2h to obtain a slurry.

[0070] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 1min, sieving to obtain a doped nano-hydroxide.

[0071] (6) The lithium cobalt oxide positive electrode material is subjected to ALD coating of Y element, and the mass ratio of Y element to lithium cobalt oxide positive electrode material is 1.75%, and a first coating layer is obtained after coating.

[0072] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat a second coating layer on the lithium cobalt oxide positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nano-hydroxide to the lithium cobalt oxide positive electrode material is 0.5%.

[0073] (8) The double-layer coated positive electrode material obtained in step (7) is sintered, the sintering temperature is controlled at 500°C, the sintering time is controlled at 8 hours, and after sintering, crushing treatment is performed.

[0074] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material is uniformly coated on an aluminum foil with carbon black and PVDF in a ratio of 90:5:5, and a lithium sheet negative electrode is formed into a coin half cell, and the coin half cell is subjected to 0.2C charging and discharging for 1 week at room temperature at 4.53V, and then is subjected to 0.5C charging to 4.6V in a 60°C oven, and is subjected to constant voltage for 300 hours, and the current curve is observed to determine the lifting time.

[0075] Example 4

[0076] (1) A 3.0ml / L cobalt sulfate solution and a 1.0mol / L manganese sulfate solution are prepared.

[0077] (2) A soluble zirconium sulfate is added to the cobalt sulfate and manganese sulfate to obtain a mixed salt solution, and the mass ratio of Zr element to the lithium cobaltate positive electrode material is 0.05%.

[0078] (3) A 4.0ml / L NaOH solution is prepared for standby use.

[0079] (4) Pure water is added to a reactor as a bottom liquid, and nitrogen is introduced as a protective atmosphere, and stirring is started and maintained at a high speed. The mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reactor, and the reaction pH value is maintained at 10 during the process. After the precipitation reaction for 5h, the rotation speed is reduced for crystallization for 2h, and a slurry is obtained.

[0080] (5) The slurry is subjected to multiple hot water washing, solid-liquid separation, drying, crushing for 1min, and sieving, and a doped nano-hydroxide is obtained.

[0081] (6) The lithium cobaltate positive electrode material is subjected to ALD coating of Zr element, and the mass ratio of Zr element to the lithium cobaltate positive electrode material is 0.05%, and a first coating layer is obtained after the coating is completed.

[0082] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat a second coating layer on the lithium cobaltate positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co and Mn elements in the nano-hydroxide to the lithium cobaltate positive electrode material is 2.0% and 0.1%, respectively.

[0083] (8) The double-coated positive electrode material obtained in step (7) is subjected to sintering, and the sintering temperature is controlled at 900°C, and the sintering time is controlled at 10 hours, and the sintering is completed, and then the sintered product is subjected to crushing treatment.

[0084] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material is uniformly coated on an aluminum foil with carbon black and PVDF in a ratio of 90:5:5, and a lithium sheet negative electrode is formed into a coin half cell, and under normal temperature conditions, 4.53V, 0.2C charging and discharging is carried out for 1 week for activation, and then the cell is charged to 4.6V at 0.5C in a 60°C oven, and the current curve is observed for 300 hours of constant voltage.

[0085] Example 5

[0086] (1) A 3.0ml / L cobalt chloride solution and a 1.0mol / L manganese chloride solution are prepared.

[0087] (2) A soluble aluminum sulfate is added to the cobalt chloride and manganese chloride solution according to the mass ratio of Al element to lithium cobaltate positive electrode material of 0.05%, to obtain a mixed salt solution.

[0088] (3) A 4.0ml / L KOH solution is prepared for standby use.

[0089] (4) Pure water is added to the reactor as a bottom liquid, and nitrogen is introduced as a protective atmosphere, and stirring is started and maintained at a high speed. The temperature is raised to 75°C, and the mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reactor, and the reaction pH value is maintained at 13 during the process. After 10h of precipitation reaction, the rotation speed is reduced for crystallization for 4h, and a slurry is obtained.

[0090] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 3min, and sieving, to obtain a doped nano-hydroxide.

[0091] (6) The lithium cobaltate positive electrode material is subjected to ALD coating of Al element, and the mass ratio of Al element in the lithium cobaltate positive electrode material is 0.05%, and a first coating layer is obtained after coating.

[0092] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat a second coating layer on the lithium cobaltate positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nano-hydroxide in the lithium cobaltate positive electrode material is 2.0%.

[0093] (8) The double-coated positive electrode material obtained in step (7) is subjected to sintering, and the sintering temperature is controlled at 1000°C, and the sintering time is controlled at 15 hours, and the sintering is completed, and then the sintered product is crushed.

[0094] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive material is uniformly coated on an aluminum foil with carbon black and PVDF in a ratio of 90:5:5, and a lithium sheet negative electrode is formed into a coin half cell, and the coin half cell is activated by charging and discharging at 0.2C for 1 week at room temperature under 4.53V, and then charged at 0.5C to 4.6V in a 60°C oven, and the current curve is observed for 300 hours under constant voltage, and the time of lifting is observed.

[0095] Example 6

[0096] (1) 1.0ml / L of cobalt chloride solution and 0.5mol / L of nickel nitrate solution are prepared.

[0097] (2) Soluble titanium chloride is added to the cobalt chloride and nickel nitrate solution according to the mass ratio of Ti element to lithium cobaltate positive material of 0.1%, to obtain a mixed salt solution.

[0098] (3) 4.0ml / L of KOH solution is prepared for standby.

[0099] (4) Pure water is added as a bottom liquid in a reaction kettle, and nitrogen gas is introduced as a protective atmosphere, and stirring is started and maintained at a high rate. The mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reaction kettle, and the reaction pH value is maintained at 13 during the process. After 10h of precipitation reaction, the rotation speed is reduced for crystallization for 4h, and a slurry is obtained.

[0100] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 3min, and sieving, to obtain a doped nano-hydroxide.

[0101] (6) The lithium cobaltate positive material and other positive materials are subjected to ALD coating of Ti element, and the mass ratio of Ti element in the lithium cobaltate positive material is 0.1%, and a first coating layer is obtained after coating.

[0102] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat a second coating layer on the lithium cobaltate positive material with a uniform first coating layer obtained in step (6), and the mass ratio of Co and Ni elements in the nano-hydroxide in the lithium cobaltate positive material is 1.1% and 0.1% respectively.

[0103] (8) The double-layer coated positive material obtained in step (7) is subjected to sintering, and the sintering temperature is controlled at 800°C, and the sintering time is controlled at 10 hours, and the sintering is completed and then subjected to crushing treatment.

[0104] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material is uniformly coated on an aluminum foil in a ratio of 90:5:5 with carbon black and PVDF, and a lithium sheet negative electrode is formed into a coin half cell, and the coin half cell is activated by charging and discharging at 0.2C for 1 week at room temperature under 4.53V, and then the coin half cell is charged at 0.5C to 4.6V in a 60°C oven, and the current curve is observed for 300 hours under constant voltage, and the time of lifting is observed.

[0105] Example 7

[0106] (1) A 1.0ml / L cobalt chloride solution is prepared.

[0107] (2) A soluble calcium nitrate is added to the cobalt chloride in a mass ratio of 0.01% of Ca element to the lithium cobaltate positive electrode material to obtain a mixed salt solution.

[0108] (3) A 2.0ml / L KOH solution is prepared for standby.

[0109] (4) Pure water is added to the reactor as a bottom liquid, and nitrogen is introduced as a protective atmosphere, and stirring is started and maintained at a high speed. The temperature is raised to 55°C, and the mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reactor, and the reaction pH value is maintained at 11 during the process. After 7h of precipitation reaction, the rotation speed is reduced for 3h of crystallization to obtain a slurry.

[0110] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 2min, and sieving to obtain a doped nano-hydroxide.

[0111] (6) The lithium cobaltate positive electrode material is subjected to Ti element ALD coating, and the mass ratio of Ti element in the lithium cobaltate positive electrode material is 0.01%, and a first coating layer is obtained after coating.

[0112] (7) The nano-hydroxide obtained in step (5) is used as an additive to coat a second coating layer on the lithium cobaltate positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nano-hydroxide to the lithium cobaltate positive electrode material is 1.1%.

[0113] (8) The double-coated positive electrode material obtained in step (7) is subjected to sintering, and the sintering temperature is controlled at 850°C, and the sintering time is controlled at 10 hours, and the sintering is completed and then subjected to crushing treatment.

[0114] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material, carbon black, and PVDF are uniformly coated on an aluminum foil in a ratio of 90:5:5 to form a coin cell half battery with a lithium sheet negative electrode, and the coin cell half battery is activated by charging and discharging at 0.2C for 1 week at a normal temperature of 4.53V, and then the coin cell half battery is charged at 0.5C to 4.6V in a 60°C oven for 300 hours, and the time when the current curve is raised is observed.

[0115] Example 8

[0116] (1) A 1.0ml / L cobalt nitrate solution is prepared.

[0117] (2) A soluble tin nitrate is added to the cobalt nitrate solution according to a mass ratio of 0.01% of Sn element in the lithium cobalt oxide positive electrode material.

[0118] (3) A 2.0ml / L KOH solution is prepared for standby use.

[0119] (4) Pure water is added to a reaction kettle as a bottom liquid, nitrogen is introduced as a protective atmosphere, stirring is started and maintained at a high speed. The mixed salt solution and the precipitant solution are simultaneously and concurrently added to the reaction kettle, and the pH value of the reaction is maintained at 11 during the process. After the precipitation reaction is performed for 7h, the rotation speed is reduced for crystallization for 3h, and a slurry is obtained.

[0120] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 2min, sieving, and a doped nano-hydroxide is obtained.

[0121] (6) The lithium cobalt oxide positive electrode material is subjected to ALD coating of Ti element, and the mass ratio of Ti element in the lithium cobalt oxide positive electrode material is 0.01%, and a first coating layer is obtained after the coating is completed.

[0122] (7) The nano-hydroxide obtained in step (5) is used as an additive to perform a second coating layer coating on the lithium cobalt oxide positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nano-hydroxide in the lithium cobalt oxide positive electrode material is 1.1%.

[0123] (8) The double-layer coated positive electrode material obtained in step (7) is subjected to sintering, the sintering temperature is controlled at 900°C, the sintering time is controlled at 8 hours, and crushing treatment is performed after the sintering is completed.

[0124] (9) The prepared sample is subjected to a coin cell floating performance test, and the test method is as follows: the positive electrode material, carbon black, and PVDF are uniformly coated on an aluminum foil in a ratio of 90:5:5 to form a coin cell half battery with a lithium sheet negative electrode, and the coin cell half battery is activated by charging and discharging at 0.2C for 1 week at a normal temperature of 4.53V, and then the coin cell half battery is charged at 0.5C to 4.6V in a 60°C oven for 300 hours, and the time when the current curve is raised is observed.

[0125] Example 9

[0126] (1) Prepare a 1.0 ml / L cobalt sulfate solution.

[0127] (2) Add soluble zinc sulfate to the cobalt sulfate solution according to the mass ratio of Zn element to lithium cobaltate positive electrode material of 0.01% to obtain a mixed salt solution.

[0128] (3) Prepare a 2.0 ml / L KOH solution for standby.

[0129] (4) Add pure water as a bottom liquid to the reactor, and pass in nitrogen as a protective atmosphere. Start stirring at a high speed. Heat to 55°C, and simultaneously and concurrently add the mixed salt solution and the precipitant solution to the reactor. Maintain the reaction pH at 11 during the process. After 7 hours of precipitation reaction, reduce the speed for crystallization for 3 hours to obtain a slurry.

[0130] (5) Wash the slurry with hot water multiple times, separate the solid and liquid, dry, crush for 2 minutes, sieve, and obtain the doped nanometer hydroxide.

[0131] (6) Perform ALD coating of Ti element on the lithium cobaltate positive electrode material and the like, and the mass ratio of Ti element to lithium cobaltate positive electrode material is 0.01%. After the coating is completed, a first coating layer is obtained.

[0132] (7) Use the nanometer hydroxide obtained in step (5) as an additive to perform a second coating layer coating on the lithium cobaltate positive electrode material and the like with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nanometer hydroxide to the lithium cobaltate positive electrode material is 1.1%.

[0133] (8) Sinter the double-layer coated positive electrode material obtained in step (7), control the sintering temperature at 900°C, and control the sintering time at 8 hours. After the sintering is completed, perform crushing treatment.

[0134] (9) Perform a button cell floating performance test on the prepared sample, and the test method is as follows: uniformly coat the positive electrode material, carbon black, and PVDF on an aluminum foil according to a ratio of 90:5:5 to form a button cell half battery with a lithium sheet negative electrode. Under normal temperature conditions, 4.53V, 0.2C charge and discharge for 1 week for activation, and then charge from 0.5C to 4.6V in a 60°C oven for 300 hours at constant voltage. Observe the time of the current curve rising.

[0135] Example 10

[0136] (1) Prepare a 1.0 ml / L cobalt sulfate solution and a 0.5 mol / L manganese nitrate solution.

[0137] (2) Add soluble magnesium sulfate and aluminum sulfate to the cobalt sulfate and manganese nitrate according to the mass ratio of Mg and Al elements in the lithium cobaltate positive electrode material of 0.01% and 0.01%, respectively, to obtain a mixed salt solution.

[0138] (3) Prepare 2.0 ml / L of KOH solution for standby.

[0139] (4) Add pure water as a bottom liquid to the reactor, and pass nitrogen gas to protect the atmosphere. Start stirring at a high speed. Heat to 55°C, and simultaneously add the mixed salt solution and the precipitant solution to the reactor. Maintain the reaction pH value at 11 during the process. After 7 hours of precipitation reaction, reduce the speed for crystallization for 3 hours to obtain a slurry.

[0140] (5) Wash the slurry with hot water for multiple times, separate the solid and liquid, dry, crush for 2 minutes, sieve, and obtain the doped nanometer hydroxide.

[0141] (6) Perform ALD coating of Ti element on the lithium cobaltate positive electrode material and the like, and the mass ratio of Ti element in the lithium cobaltate positive electrode material is 0.01%. After the coating is completed, a first coating layer is obtained.

[0142] (7) Use the nanometer hydroxide obtained in step (5) as an additive to perform a second coating layer coating on the lithium cobaltate positive electrode material with a uniform first coating layer obtained in step (6), and the mass ratio of Co element in the nanometer hydroxide in the lithium cobaltate positive electrode material is 1.1%.

[0143] (8) Sinter the double-layer coated positive electrode material obtained in step (7), control the sintering temperature at 900°C, and control the sintering time at 8 hours. After the sintering is completed, perform crushing treatment.

[0144] (9) Perform the performance test of the prepared sample in the button cell floating charge, and the test method is as follows: uniformly coat the positive electrode material, carbon black, and PVDF on the aluminum foil according to the ratio of 90:5:5, and form a button half cell with a lithium sheet negative electrode. Under the condition of normal temperature, 4.53V, and 0.2C charge and discharge for 1 week, activate, and then charge from 0.5C to 4.6V in a 60°C oven, and maintain the voltage for 300 hours. Observe the time of the current curve rising.

[0145] Example 11

[0146] (1) Prepare 1.0 ml / L of cobalt nitrate solution and 1.0 mol / L of nickel sulfate solution.

[0147] (2) Add soluble magnesium sulfate and titanium chloride to the cobalt nitrate and nickel sulfate according to the mass ratio of Mg and Ti elements in the lithium cobaltate positive electrode material of 0.01% and 0.005%, respectively, to obtain a mixed salt solution.

[0148] (3) Prepare 2.0 ml / L of KOH solution for standby.

[0149] (4) Add pure water as a bottom liquid into the reactor, and introduce nitrogen as a protective atmosphere. Start stirring at a high speed. Heat to 55°C, and simultaneously add the mixed salt solution and the precipitant solution into the reactor. Keep the pH value at 11 during the process. After 7 hours of precipitation reaction, reduce the stirring speed for 3 hours of crystallization to obtain a slurry.

[0150] (5) Wash the slurry with hot water for multiple times, separate the solid from the liquid, dry, crush for 2 minutes, sieve, and obtain the doped nanometer hydroxide.

[0151] (6) Perform ALD coating of Ti element on the first product of the lithium cobaltate positive electrode material. The mass ratio of Ti element in the lithium cobaltate positive electrode material is 0.005%, and the first coating layer is obtained after the coating is completed.

[0152] (7) Use the nanometer hydroxide obtained in step (5) as an additive to perform second coating on the lithium cobaltate positive electrode material with the uniform first coating layer obtained in step (6). The mass ratio of Co element in the nanometer hydroxide in the lithium cobaltate positive electrode material is 1.1%.

[0153] (8) Sinter the double-coated positive electrode material obtained in step (7). The sintering temperature is controlled at 900°C, and the sintering time is controlled at 8 hours. After the sintering is completed, perform crushing treatment.

[0154] (9) Perform the performance test of the prepared sample in a button cell. The test method is as follows: uniformly coat the positive electrode material, carbon black, and PVDF on an aluminum foil in a ratio of 90:5:5 to form a button cell with a lithium sheet negative electrode. Activate by charging and discharging at 0.2C for 1 week at a normal temperature of 4.53V, and then charge at 0.5C to 4.6V in a 60°C oven for 300 hours at a constant voltage. Observe the time of the current curve rising.

[0155] Example 12

[0156] (1) Prepare 1.0 ml / L of cobalt nitrate solution and 1.0 mol / L of nickel chloride solution.

[0157] (2) Add soluble lanthanum sulfate and yttrium sulfate to the cobalt nitrate and nickel chloride solutions in a mass ratio of 0.1% and 0.1% of La and Y elements in the lithium cobaltate positive electrode material, respectively, to obtain a mixed salt solution.

[0158] (3) Prepare 2.0 ml / L of ammonia solution for standby.

[0159] (4) The reactor is filled with pure water as a bottom liquid, nitrogen is introduced as a protective atmosphere, stirring is started and kept at a high rate. The temperature is raised to 55°C, the mixed salt solution and the precipitant solution are simultaneously and co-currently introduced into the reactor, the pH value is kept at 11 during the process, after 7h of precipitation reaction, the rotation speed is reduced for 3h of crystallization, and the slurry is obtained.

[0160] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 2min, sieving, and the doped nanometer hydroxide is obtained.

[0161] (6) The lithium cobaltate and other positive electrode materials are coated with Al and Ti elements by ALD, the mass ratio of Al and Ti elements in the lithium cobaltate positive electrode material is 0.01% and 0.01% respectively, and the first coating layer is obtained after the coating is completed.

[0162] (7) The nanometer hydroxide obtained in step (5) is used as an additive to coat the lithium cobaltate and other positive electrode materials with uniform first coating layer obtained in step (6) with a second coating layer, wherein the mass ratio of Co element in the nanometer hydroxide to the lithium cobaltate positive electrode material is 1.1%.

[0163] (8) The double-coated positive electrode material obtained in step (7) is sintered, the sintering temperature is controlled at 950°C, the sintering time is controlled at 10 hours, and the crushing treatment is performed after the sintering is completed.

[0164] (9) The prepared sample is subjected to the performance test of the button cell floating charge, and the test method is as follows: the positive electrode material, carbon black and PVDF are uniformly coated on the aluminum foil in a ratio of 90:5:5 to form a button half cell with a lithium sheet negative electrode, the button half cell is activated by 0.2C charging and discharging for 1 week under normal temperature condition of 4.53V, and the button half cell is observed for the time of current curve rising in the constant voltage of 0.5C charging to 4.6V in the oven at 60°C for 300 hours. Figure 2 is the SEM picture of La, Y doped Co 0.8 Ni 0.2 (OH)2(La0.1%, Y0.1%) of the present embodiment.

[0165] Example 13

[0166] (1) 1.0ml / L of cobalt acetate solution, 3.0mol / L of nickel acetate solution and 3.0mol / L of manganese acetate solution are configured.

[0167] (2) The soluble lanthanum sulfate, yttrium sulfate and manganese sulfate are added to the cobalt acetate, nickel acetate and manganese acetate in a mass ratio of 0.1%, 0.1% and 0.1% of La, Y and Zr elements to the lithium cobaltate positive electrode material, and the mixed salt solution is obtained.

[0168] (3) 2.0ml / L of ammonia solution is prepared for standby.

[0169] (4) The reactor is added with pure water as a bottom liquid, nitrogen is introduced as a protective atmosphere, stirring is started and kept at a high rate. The temperature is raised to 55°C, the mixed salt solution and the precipitant solution are simultaneously and concurrently added into the reactor, the pH value is kept at 12 during the process, the precipitation reaction is carried out for 8 hours, then the rotation speed is reduced for crystallization for 3 hours, and the slurry is obtained.

[0170] (5) The slurry is washed with hot water for multiple times, solid-liquid separation, drying, crushing for 2 minutes, sieving, and the doped nanometer hydroxide is obtained.

[0171] (6) The lithium cobaltate and other positive electrode materials are coated with Al and Ti elements by ALD, the mass ratio of Al and Ti elements in the lithium cobaltate positive electrode material is 0.01% and 0.01% respectively, and the first coating layer is obtained after the coating is completed.

[0172] (7) The nanometer hydroxide obtained in step (5) is used as an additive to coat the lithium cobaltate and other positive electrode materials with the uniform first coating layer obtained in step (6) with a second coating layer, wherein the mass ratio of Co and Ni elements in the nanometer hydroxide in the lithium cobaltate positive electrode material is 1.1% and 0.1% respectively.

[0173] (8) The double-coated positive electrode material obtained in step (7) is sintered, the sintering temperature is controlled at 910°C, the sintering time is controlled at 9 hours, and the crushing treatment is carried out after the sintering is completed.

[0174] (9) The prepared sample is tested for the performance of the button cell floating charge, and the test method is as follows: the positive electrode material, carbon black and PVDF are uniformly coated on the aluminum foil in a ratio of 90:5:5 to form a button cell half-cell with a lithium sheet negative electrode, the button cell is activated by charging and discharging at 0.2C for 1 week under normal temperature condition of 4.53V, and then the button cell is charged at 0.5C to 4.6V in a 60°C oven for 300 hours under constant voltage, and the current curve is observed to determine the lifting time.

[0175] Example 14

[0176] (1) A 2.0ml / L cobalt acetate solution, a 2.0ml / L nickel sulfate, nickel chloride solution, a 2.0ml / L manganese sulfate, manganese chloride solution is configured.

[0177] (2) The soluble aluminum sulfate and titanium chloride are added into the cobalt acetate, nickel sulfate, nickel chloride, manganese sulfate and manganese chloride in a mass ratio of 0.005% and 0.005% of Al and Ti elements in the lithium cobaltate positive electrode material to obtain a mixed salt solution.

[0178] (3) A 1.0ml / L ammonia solution is prepared for standby.

[0179] (4) The reactor is filled with pure water as the bottom liquid, and nitrogen is introduced as the protective atmosphere. Stirring is started and maintained at a high speed. The temperature is raised to 55°C, and the mixed salt solution and the precipitant solution are simultaneously and co-currently added to the reactor. The pH value is maintained at 12 during the process. After 8 hours of precipitation reaction, the rotation speed is reduced for crystallization for 3 hours, and the slurry is obtained.

[0180] (5) The slurry is washed with hot water for multiple times, and solid-liquid separation, drying, and crushing are performed for 2 minutes. The product is sieved to obtain the doped nanometer hydroxide.

[0181] (6) The lithium cobaltate positive electrode material is coated with Al and Ti elements by ALD. The mass ratio of Al and Ti elements in the lithium cobaltate positive electrode material is 0.005% and 0.005%, respectively. After the coating is completed, the first coating layer is obtained.

[0182] (7) The nanometer hydroxide obtained in step (5) is used as an additive to coat the lithium cobaltate positive electrode material with the uniform first coating layer obtained in step (6) with a second coating layer. The mass ratio of Co, Ni, and Mn elements in the nanometer hydroxide in the lithium cobaltate positive electrode material is 1.1%, 0.1%, and 0.1%, respectively.

[0183] (8) The double-coated positive electrode material obtained in step (7) is sintered. The sintering temperature is controlled at 900°C, and the sintering time is controlled at 10 hours. After sintering, the product is crushed.

[0184] (9) The prepared sample is subjected to a coin cell floating performance test. The test method is as follows: the positive electrode material, carbon black, and PVDF are uniformly coated on an aluminum foil in a ratio of 90:5:5 to form a coin cell half-battery with a lithium sheet negative electrode. The coin cell half-battery is activated by charging and discharging at 0.2C for 1 week at a constant temperature of 4.53V. Then, the coin cell half-battery is charged at 0.5C to 4.6V in an oven at 60°C, and the voltage is maintained for 300 hours. The current curve is observed to determine the time of the upward curve.

[0185] Example 15

[0186] (1) A 2.0ml / L cobalt acetate solution, a 2.0ml / L nickel sulfate solution, a 2.0ml / L manganese sulfate solution, a 2.0ml / L manganese chloride solution, and a 2.0ml / L manganese nitrate solution are prepared.

[0187] (2) The soluble lanthanum sulfate, yttrium sulfate, zirconium sulfate, aluminum sulfate, and titanium chloride are added to the cobalt acetate, nickel sulfate, nickel chloride, nickel nitrate, nickel acetate, manganese sulfate, manganese chloride, and manganese nitrate in a mass ratio of 0.1%, 0.1%, 0.1%, 0.005%, and 0.005%, respectively, to obtain a mixed salt solution.

[0188] (3) Prepare 1.0 ml / L of ammonia solution for use.

[0189] (4) Add pure water as a bottom liquid to the reactor, and pass in nitrogen as a protective atmosphere. Start stirring at a high speed. Heat to 55°C, and simultaneously and concurrently add the mixed salt solution and the precipitant solution to the reactor. Maintain the reaction pH at 12 during the process. After 8 hours of precipitation reaction, reduce the rotation speed for 3 hours of crystallization to obtain a slurry.

[0190] (5) Wash the slurry with hot water for multiple times, separate the solid and liquid, dry, crush for 2 minutes, sieve, and obtain the doped nanometer hydroxide.

[0191] (6) Perform ALD coating of Al and Ti elements on the primary product of the lithium cobalt oxide and other positive electrode materials, and the mass ratio of Al and Ti elements in the lithium cobalt oxide positive electrode material is 0.005% and 0.005%. After the coating is completed, a first coating layer is obtained.

[0192] (7) Use the nanometer hydroxide obtained in step (5) as an additive to perform a second coating layer coating on the lithium cobalt oxide and other positive electrode materials with the uniform first coating layer obtained in step (6), and the mass ratio of Co, Ni, and Mn elements in the nanometer hydroxide in the lithium cobalt oxide positive electrode material is 1.1%, 0.1%, and 0.1% respectively.

[0193] (8) Sinter the double-coated positive electrode material obtained in step (7), control the sintering temperature at 900°C, and control the sintering time at 10 hours. After the sintering is completed, perform crushing treatment.

[0194] (9) Perform the performance test of the prepared sample in a button cell. The test method is as follows: uniformly coat the positive electrode material, carbon black, and PVDF on an aluminum foil in a ratio of 90:5:5 to form a button cell with a lithium sheet negative electrode. Activate by charging and discharging at 0.2C for 1 week at a normal temperature of 4.53V, and then charge at 0.5C to 4.6V in a 60°C oven for 300 hours at a constant voltage. Observe the time of the current curve rising.

[0195] Comparative Example

[0196] Perform dry coating of Co, Ti, and Ni elements on the primary product of the lithium cobalt oxide and other positive electrode materials in the form of Co(OH)2, TiO2, and NiO, and the mass ratio of Co, Ti, and Ni elements in the lithium cobalt oxide positive electrode material is 1.1%, 0.1%, and 0.1% respectively. After the coating is completed, perform sintering on the positive electrode material, control the sintering temperature at 800°C, control the sintering time at 10 hours, and perform crushing treatment after the sintering is completed.

[0197] The prepared sample was subjected to the performance test of the coin cell floating charge, and the test method was as follows: the positive material, carbon black and PVDF were uniformly coated on the aluminum foil in a ratio of 90:5:5 to form a coin half cell with a lithium sheet negative electrode, and the coin half cell was activated by 0.2C charge-discharge at room temperature for 1 week, and then was subjected to 0.5C charging to 4.6V in a 60°C oven, and the current curve was observed for the lifting time.

[0198] Figure 3 The element doping depth of Ni element of the examples 6 and the comparative examples was compared.

[0199] The element doping depth of the above examples and comparative examples and the test results of the 4.6V coin cell floating charge were shown in Table 1, and the corresponding trend of the element doping depth and the 4.6V coin cell floating charge was shown in Figure 4 .

[0200] Table 1

[0201] Working Example Elemental Doping Depth (nm) 4.6V pull-down float charge (h) 1 270 30 2 220 60 3 70 200 4 94 150 5 83 160 6 140 100 7 265 40 8 273 30 9 260 45 10 86 165 11 90 155 12 84 175 13 43 270 14 42 275 15 40 280 Comparative Example 300 10

[0202] According to Figure 3 , Figure 4 and Table 1, it can be seen that the element doping depth of the sample of the examples of the present application is lower, which can effectively keep the coating element on the surface of the positive material, and plays the role of isolating the electrolyte and protecting the surface positive material. At the same time, as the data shows, the element doping depth and the 4.6V coin cell floating charge are obviously negatively correlated, and the sample of the present application effectively improves the 4.6V coin cell floating charge performance of the positive material.

[0203] The above disclosed specific embodiments of the present application are intended to help understand the content of the present application and to implement the same, and those skilled in the art can understand that various substitutions, changes and modifications are possible without departing from the spirit and scope of the present application. The present application should not be limited to the content disclosed in the examples of the present application, and the protection scope of the present application is defined by the scope of the claims.

Claims

1. A multi-layer coated positive electrode material, characterized in that: Its structural formula is LizMAO2, M=Ni 1-x-y Mn x Co y , 0<y≤1, 1<z≤1.2, M is at least one of the transition metals Ni, Co, and Mn, and the modifying element A is at least one of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn; The multi-layer coated positive electrode material includes a first coating layer and a second coating layer; The first coating layer is uniformly coated on the surface of the base material, and the coating element is selected from at least one of Mg, Ti, Al, La, Y, and Zr; The second coating layer is coated on the surface of the first coating layer, and its coating element is selected from one or more of Mg, Ti, Al, La, Y, Zr, Co, Ni, Mn, Ca, Sn, and Zn, and contains at least one of Co, Ni, and Mn; By introducing the first coating layer for uniform coating and regulating the thickness, the diffusion of elements between the substrate and the second coating layer is controlled, thereby forming a specific surface doping coating structure and maintaining the coating elements on the surface of the positive electrode material; the second coating layer is introduced in the form of a doped hydroxide to avoid competitive reactions between elements, which is beneficial to the control of surface morphology and the improvement of coating uniformity; The multi-layer coated positive electrode material is prepared by the following steps: Performing ALD coating on the base material to obtain a first coating layer; Preparation of doped nano hydroxides; Using doped nano hydroxide as an additive to coat the base material having the first coating layer with a second coating layer to obtain a double-layer coated positive electrode material; The double-layer coated positive electrode material is sintered and crushed to obtain a final positive electrode material; The method for preparing the doped nano hydroxide comprises: Weighing a certain amount of nickel-cobalt-manganese salt raw material and dissolving it in water to obtain a nickel-cobalt-manganese salt solution; the nickel-cobalt-manganese salt contains at least one of the three elements Ni, Co, and Mn; A soluble salt raw material containing at least one element of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn is added to a nickel-cobalt-manganese salt solution in a stoichiometric ratio to obtain a mixed salt solution; Pure water is added to the reactor as the base liquid, nitrogen is introduced as a protective atmosphere, stirring is started and maintained at a high speed, the temperature is raised to a certain temperature, and the mixed salt solution and the precipitant solution are simultaneously added to the reactor in parallel, and the reaction pH value is maintained at 10 to 13 during the process. After the precipitation reaction is carried out for 5 to 10 hours, the rotation speed is reduced and crystallization is carried out for 2 to 4 hours to obtain a slurry; The slurry is subjected to multiple hot water washing, solid-liquid separation, drying, crushing, and sieving to obtain doped nano hydroxide.

2. The multi-layer coated positive electrode material according to claim 1, characterized in that The first coating layer is introduced by ALD uniform coating, and the coating thickness is 0.05-50nm.

3. The multi-layer coated positive electrode material according to claim 1, characterized in that The particle size of the doped hydroxide is controlled to nanometer level, 10nm to 900nm; the doping element of the doped hydroxide is introduced by precursor precipitation.

4. A method for preparing the multi-layer coated positive electrode material according to claim 1, characterized in that: The following steps are involved: Performing ALD coating on the base material to obtain a first coating layer; Preparation of doped nano hydroxides; Using doped nano hydroxide as an additive to coat the base material having the first coating layer with a second coating layer to obtain a double-layer coated positive electrode material; The double-layer coated positive electrode material is sintered and crushed to obtain a final positive electrode material; The method for preparing the doped nano hydroxide comprises: Weighing a certain amount of nickel-cobalt-manganese salt raw material and dissolving it in water to obtain a nickel-cobalt-manganese salt solution; the nickel-cobalt-manganese salt contains at least one of the three elements Ni, Co, and Mn; A soluble salt raw material containing at least one element of Mg, Ti, Al, La, Y, Zr, Ni, Mn, Ca, Sn, and Zn is added to a nickel-cobalt-manganese salt solution in a stoichiometric ratio to obtain a mixed salt solution; Pure water is added to the reactor as the base liquid, nitrogen is introduced as a protective atmosphere, stirring is started and maintained at a high speed, the temperature is raised to a certain temperature, and the mixed salt solution and the precipitant solution are simultaneously added to the reactor in parallel, and the reaction pH value is maintained at 10 to 13 during the process. After the precipitation reaction is carried out for 5 to 10 hours, the rotation speed is reduced and crystallization is carried out for 2 to 4 hours to obtain a slurry; The slurry is subjected to multiple hot water washing, solid-liquid separation, drying, crushing, and sieving to obtain doped nano hydroxide.

5. The method according to claim 4, characterized in that The precipitant is one of sodium hydroxide, potassium hydroxide and ammonia water, and the concentration of the precipitant is 0.5-4 mol / L.

6. The method according to claim 4, characterized in that The coating element of the first coating layer is introduced through a metal organic salt; the metal organic salt is at least one of bis(ethylcyclopentadienyl)magnesium, titanium tetraisopropoxide, trimethylaluminum, tri(isopropylcyclopentadienyl)lanthanum, and tri(N,N'-diisopropylacetamidine)yttrium.

7. The method according to claim 4, characterized in that The sintering temperature is controlled at 500-1050° C., and the sintering time is controlled at 8-20 hours.

8. The method according to claim 4, characterized in that The method also includes the step of conducting a button battery float charge performance test on the prepared positive electrode material, wherein the button battery float charge performance test comprises: uniformly coating the positive electrode material, carbon black and PVDF in a ratio of 90:5:5 on aluminum foil, and forming a button half-cell with a lithium sheet negative electrode, and activating the battery by charging and discharging at 4.53V and 0.2C for one week at room temperature, and then charging from 0.5C to 4.6V in a 60°C oven and maintaining a constant voltage for 300 hours, and observing the time when the current curve rises.

Images