CN112086679B - High-nickel ternary material, surface modification method and lithium ion battery - Google Patents

High-nickel ternary material, surface modification method and lithium ion battery Download PDF

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CN112086679B
CN112086679B CN202011064171.2A CN202011064171A CN112086679B CN 112086679 B CN112086679 B CN 112086679B CN 202011064171 A CN202011064171 A CN 202011064171A CN 112086679 B CN112086679 B CN 112086679B
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additive
ternary material
nickel ternary
surface modification
modification method
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闵长青
王振昆
龙君君
高玉仙
丁楚雄
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Guoxuan High Tech Power Energy Co Ltd
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    • H01—ELECTRIC ELEMENTS
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    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
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    • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
    • H—ELECTRICITY
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    • H01M4/02—Electrodes composed of, or comprising, active material
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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Abstract

The invention discloses a high-nickel ternary material, a surface modification method and a lithium ion battery+As a first additive, and then introduces TiOSO4An acidic solution, and the third additive is Al2(SO4)3The fourth additive is NaAlO2And (3) alkaline solution, and finally separating, drying and calcining to obtain the surface-modified high-nickel ternary material. The high-nickel ternary material obtained by the surface modification method can effectively reduce the surface residual alkali of the high-nickel ternary material and improve the structural stability.

Description

High-nickel ternary material, surface modification method and lithium ion battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a surface modification method of a high-nickel ternary material, the high-nickel ternary material obtained by the surface modification method, and a lithium ion battery containing the high-nickel ternary material.
Background
With the development of new energy automobiles, the demand and the requirement on new energy power batteries are increased, and in 2020, the specific energy of a new energy power battery monomer is required to be more than 300Wh/kg, and the aim is to achieve 350 Wh/kg. However, the maximum energy density of the lithium iron phosphate battery is only 200Wh/kg at present, which is far from the target of 300 Wh/kg. Therefore, the ternary material battery plays a strong role, and considering the energy density increase demand of the power battery and the influence of global cobalt price rise, the low-cobalt high-nickel ternary material battery becomes a key point.
With the increase of the nickel content, the surface alkali (LiOH and Li) of the nickel-cobalt-manganese ternary cathode material2CO3) The content of residual alkali is increasedThe pH value of the material is only increased, so that the material is easy to form jelly due to water absorption in the homogenization process, the processing performance of the positive electrode material is reduced, side reaction is generated with electrolyte in the charge-discharge cycle process, the irreversible capacity loss of the battery is increased, the cycle performance is deteriorated, the battery expands, and the potential safety hazard exists in the battery.
At present, a water washing method is usually adopted in industrial production to solve the problem of excessive residual alkali content on the surface of the high-nickel ternary material. Although the water washing process is simple and easy to implement, and can effectively reduce the surface alkali residue, the high-nickel ternary material is sensitive to moisture, and long-time contact can cause lithium in crystal lattices to be washed out, so that the crystal structure of the surface of the material is changed, and the electrochemical performance of the material is deteriorated.
Disclosure of Invention
In view of the above, the present invention is necessary to provide a surface modification method for high nickel ternary material by introducing Li during the washing process of high nickel ternary material+Effective inhibition of Li in the matrix of the material+Excessive precipitation of (2) and stabilization of the structure, while adding TiO2+、Al3+And AlO2 -Double hydrolysis occurs to form Al (OH) on the surface of the material3And Ti (OH)4Then sintering at high temperature to generate Al with uniform components and controllable thickness2O3And TiO2The coating layer effectively reduces the surface residual alkali of the high-nickel ternary material and improves the structural stability so as to solve the problems.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a surface modification method of a high-nickel ternary material, which comprises the following steps:
adding a first additive and high-nickel ternary material calcined powder into deionized water, and uniformly stirring to obtain a first slurry, wherein the first additive is cation Li+A soluble salt of (a);
simultaneously dripping a second additive, a third additive and a fourth additive into the first slurry, and continuously stirring to obtain a second slurry after dripping is finished, wherein the second additive is TiOSO4Acid solutionLiquid, the third additive is Al2(SO4)3The fourth additive is NaAlO2An alkaline solution;
and centrifuging the second slurry, dynamically rotating, drying and calcining to obtain the surface-modified high-nickel ternary material.
Furthermore, the chemical formula of the high-nickel ternary material calcined powder is LiNixCoyM1-x-yO2Wherein M is at least one of Mn, Al, Zr, Ti and Mg, x is more than or equal to 0.60, and y is less than or equal to 0.20.
Further, the soluble salt is selected from at least one of sulfate, nitrate, phosphate and chloride;
in the first additive, the cation Li+The effective ion content of the high-nickel ternary material is 0.001-0.1wt%, the addition amount of the first additive is 3-10% of the mass of the high-nickel ternary material calcined powder, and the solid-liquid mass ratio of the high-nickel ternary material calcined powder to the deionized water is 1: 0.5-5.
Furthermore, the addition amount of the second additive is 1-10% of the mass of the high-nickel ternary material calcined powder, and the second additive, the third additive and the fourth additive are TiO according to the mass ratio2+:Al3+:AlO2 -The addition is carried out in a molar ratio of 1:1:5, wherein the effective ion content of the second additive, the third additive and the fourth additive is 0.001-0.1 wt%.
Further, the TiOSO4Acid solution, Al2(SO4)3The acid solutions in the acid solutions are respectively and independently selected from at least one of sulfuric acid solution, hydrochloric acid solution, acetic acid solution, nitric acid solution and citric acid solution;
the NaAlO2The alkaline solution in the alkaline solution is at least one selected from sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution and ammonia water solution.
Further, the dropping time of the second additive, the third additive and the fourth additive is controlled within 3-10 min.
Further, the dynamic rotary drying is carried out by adopting a vacuum coulter, the rotating speed is kept at 3-20r/min, the drying temperature is 120-.
Further, the sintering temperature of the calcination is 500-700 ℃, and the heat preservation time is 3-7 h.
The invention also provides a high-nickel ternary material which is obtained by surface modification through the surface modification method in any one of the above-mentioned methods.
The invention further provides a lithium ion battery, which contains the high-nickel ternary material.
Compared with the prior art, the invention has the following beneficial effects:
the surface modification method of the high-nickel ternary material introduces Li in the water washing process+Cation, thereby effectively inhibiting Li in the high-nickel ternary material matrix+Excessive precipitation is carried out, the stable structure of the high-nickel ternary material matrix is protected, and the problem of poor electrochemical performance of the high-nickel ternary material due to washing is avoided; further, TiO is added in the water washing process2+、Al3+、AlO2 -Ions which can be subjected to double hydrolysis in an alkaline environment to form a hydroxide coating layer on the surface of the high-nickel ternary material, and then the hydroxide is dehydrated through high-temperature sintering to generate metal oxide TiO2、Al2O3And (4) coating. The coating has uniform components and controllable thickness.
The surface modification method can effectively reduce the residual alkali content on the surface of the high-nickel ternary material, reduce the contact area between the material and the electrolyte, avoid the occurrence of side reaction and improve the cycle performance of the high-nickel ternary material; and the excessive precipitation of lithium in the matrix is avoided, the stability of the structure is ensured, and the electrochemical performance deterioration of the high-nickel ternary material is avoided.
Drawings
FIG. 1 shows Al in example 12O3And TiO2Coated LiNi0.85Co0.10Mn0.05O2Transmission electron microscopy images of;
FIG. 2 shows Al in example 12O3And TiO2Coated LiNi0.85Co0.10Mn0.05O2Scanning electron microscope images of;
FIG. 3 shows Al in comparative example 12O3And TiO2Coated LiNi0.85Co0.10Mn0.05O2Scanning electron microscope images of;
fig. 4 is a graph of the rate cycles of assembling lithium ion batteries from the high nickel ternary materials in example 1, comparative example 2 and comparative example 3.
Detailed Description
In order that the invention may be more fully understood, reference will now be made to the specific embodiments illustrated. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.
The invention discloses a surface modification method of a high-nickel ternary material, which comprises the following steps:
adding a first additive and high-nickel ternary material calcined powder into deionized water, and uniformly stirring to obtain a first slurry, wherein the first additive is cation Li+A soluble salt of (a);
simultaneously dripping a second additive, a third additive and a fourth additive into the first slurry, and continuously stirring to obtain a second slurry after dripping is finished, wherein the second additive is TiOSO4An acidic solution, and the third additive is Al2(SO4)3The fourth additive is NaAlO2An alkaline solution;
and centrifuging the second slurry, dynamically rotating, drying and calcining to obtain the surface-modified high-nickel ternary material.
In the surface modification method, the high-nickel ternary material calcined powder refers to a block material obtained by sintering a precursor containing a nickel source and a lithium source for the first time in a conventional washing process, and then the block material is crushed and sieved to obtain powder and then washed with water, wherein the high-nickel ternary material calcined powder refers to powder obtained by crushing and sieving the block material before the conventional washing. The stirring aims to ensure that the materials are uniformly dispersed in water and fully washed, the rotating speed is generally preferably 50-200 r/min, the stirring time is not particularly limited and can be adjusted as required; similarly, the second slurry is centrifuged mainly for the purpose of solid-liquid separation, and therefore, the second slurry is not particularly limited as long as the solid-liquid separation can be achieved, and the centrifugation speed is preferably 1500 to 3000 r/min.
Aiming at the problem of reducing surface residual alkali in the existing high-nickel ternary material washing, the invention innovatively firstly mixes the high-nickel ternary material calcined powder with Li added with cations+By stirring the soluble salt in deionized water, and by this process, introducing Li+When two salts (or acid and alkali) containing the same ions are dissolved in water, the solubility (or acidity coefficient) of the two salts is reduced, and the Li in the high-nickel ternary material matrix is effectively inhibited by utilizing the' same ion effect+Excessive precipitation ensures the structural stability of the high-nickel ternary material in the washing process, and avoids the problem of poor electrochemical performance of the high-nickel ternary material caused by washing; further, TiO is introduced2+、Al3+、AlO2 -Ions which can be subjected to double hydrolysis in an alkaline environment to form a hydroxide coating layer on the surface of the high-nickel ternary material, and the formed hydroxide coating layer is sintered at high temperature to obtain a corresponding oxide coating layer which is uniform in component and can be obtained by adjusting TiO2+、Al3+、AlO2 -The thickness of the coating layer is controlled by the addition amount of ions, so that the thickness of the coating layer is controllable, and the residual alkali content on the surface of the high-nickel ternary material is effectively reducedAnd the electrochemical performance of the material is improved.
Further, the composition of the high nickel ternary material in the present invention is not particularly limited, and the high nickel ternary material conventionally defined in the art may be prepared by the surface modification method in the present invention, and in some specific embodiments of the present invention, the chemical formula composition of the high nickel ternary material calcined powder is LiNixCoyM1-x-yO2Wherein M is at least one of Mn, Al, Zr, Ti and Mg, x is more than or equal to 0.60, and y is less than or equal to 0.20.
Further, the soluble salt may be a soluble salt species conventional in the art, and specific examples include but are not limited to at least one of sulfate, nitrate, phosphate, chloride, such as lithium sulfate, lithium chloride, and the like;
preferably, in the first additive, the cation Li+The effective ion content of the high-nickel ternary material is 0.001-0.1wt%, the addition amount of the first additive is 3-10% of the mass of the high-nickel ternary material calcined powder, and the solid-liquid mass ratio of the high-nickel ternary material calcined powder to the deionized water is 1: 0.5-5, and preferably, the solid-to-liquid ratio of the high-nickel ternary material calcined powder to the deionized water is 1:1.
further, the addition amount of the second additive, the third additive and the fourth additive is not particularly limited, and the thickness of the coating layer can be adjusted according to the addition amount, preferably, the addition amount of the second additive is 1-10% of the mass of the high-nickel ternary material calcined powder, and the second additive, the third additive and the fourth additive are TiO2+:Al3+:AlO2 -The molar ratio is 1:1:5, wherein the effective ion content in the second additive, the third additive and the fourth additive is 0.001-0.1 wt%.
Further, the TiOSO4Acid solution, Al2(SO4)3The acid solutions in the acid solutions are respectively and independently selected from at least one of sulfuric acid solution, hydrochloric acid solution, acetic acid solution, nitric acid solution and citric acid solution;
the NaAlO2The alkaline solution in the alkaline solution is at least one selected from sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution and ammonia water solution.
By using TiO2+、Al3+And AlO2 -Ions are subjected to double hydrolysis reaction in an alkaline environment, so that a hydroxide coating layer is formed on the surface of the high-nickel ternary material, and the hydroxide is dehydrated through high-temperature sintering to obtain an oxide coating layer, so that the surface residual alkali content of the high-nickel ternary material is reduced, the contact area of the material and an electrolyte is reduced, side reaction is avoided, and the cycle performance of the high-nickel ternary material is improved.
Preferably, in order to control the uniformity of the hydroxide coating layer, the second additive, the third additive and the fourth additive are added dropwise in the present invention, so that the double hydrolysis reaction is sufficiently performed and a uniform hydroxide coating layer is formed, and the adding time is not particularly limited and may be 2min, 3min, 5min, 9min, 10min, and the like, and preferably, in some specific embodiments of the present invention, the adding time is controlled to be 3-10 min.
Preferably, the dynamic rotary drying is performed by vacuum coulter drying, so that on one hand, vacuum in a coulter kettle is maintained, the volatilization of the moisture of the material is facilitated, and the contact of the material and carbon dioxide in the air is avoided as much as possible, so that the generation of lithium carbonate is reduced, on the other hand, the heated area of the material can be increased by the coulter rotary drying, and the volatilization of the moisture in the material is facilitated, and in some specific embodiments of the invention, the rotating speed is 3-20r/min, the drying temperature is 120-.
Preferably, the sintering temperature of the calcination is 500-700 ℃, and the heat preservation time is 3-7 h.
The second aspect of the invention discloses a high-nickel ternary material, which is obtained by surface modification through the surface modification method of the first aspect of the invention, and the high-nickel ternary material is low in residual alkali content and excellent in performance through tests.
In a third aspect, the invention discloses a lithium ion battery, which contains the high-nickel ternary material according to the second aspect of the invention.
The technical solution of the present invention will be further clearly described with reference to specific examples.
Example 1
Pouring 50kg of deionized water into a washing kettle with polytetrafluoroethylene as a lining, adding a first additive consisting of a lithium sulfate solution into the deionized water, uniformly stirring, and then mixing the high-nickel ternary material calcined powder and the deionized water according to a solid-to-liquid ratio of 1:1 addition of LiNi0.85Co0.10Mn0.05O2Sintering the powder, stirring at high speed to form uniform first slurry, wherein in the first additive, Li+The effective ion content is 0.05 wt%, and the addition amount of the first additive is 5 wt% of the mass of the added high-nickel ternary material calcined powder.
According to TiO aspect2+:Al3+:AlO2 -TiOSO is simultaneously added dropwise to the first slurry at a molar ratio of 1:1:5 in an amount of 0.01 wt% of available ion content4Sulfuric acid solution, 0.01 wt% Al2(SO4)3Sulfuric acid solution and 0.05 wt% NaAlO2Sodium hydroxide solution, TiOSO4The amount of the sulfuric acid solution added was LiNi0.85Co0.10Mn0.05O2And 2% of the powder, controlling the dropping time to be 2min, and continuing to stir at a high speed for 5min after the dropping is finished to obtain a second slurry.
And centrifugally separating the second slurry, and then placing the second slurry in coulter drying equipment for vacuum drying, wherein the rotating speed of the coulter is 3r/min, the drying temperature is 150 ℃, the drying time is 8h, and the vacuum degree is set to be-0.06 MPa. Placing the dried material in a muffle furnace, heating to 670 ℃ in an oxygen environment, preserving heat for 5 hours, and naturally cooling to room temperature to obtain the coated TiO2And Al2O3LiNi of (2)0.85Co0.10Mn0.05O2A high nickel ternary material.
Comparative example 1
LiNi which is a high-nickel ternary material in example 10.85Co0.10Mn0.05O2Sintering powder and nano Al2O3And nano TiO2(D50 is 50nm or less) and the Ti element and Al element were added in the same amounts as in example 1.
Placing the uniformly mixed powder in a muffle furnace, heating to 670 ℃ in an oxygen atmosphere, preserving the heat for 5 hours, and naturally cooling to room temperature to obtain the coated Al2O3And TiO2LiNi of (2)0.85Co0.10Mn0.05O2。
Comparative example 2
In the washing process of example 1, the TiOSO solution was added directly without adding the lithium sulfate solution4Sulfuric acid solution, Al2(SO4)3Sulfuric acid solution and NaAlO2The sodium hydroxide solution, the amount added and other steps were the same as in example 1.
Comparative example 3
In the washing process of example 1, only the lithium sulfate solution was added without dropwise addition of TiOSO4Sulfuric acid solution, Al2(SO4)3Sulfuric acid solution and NaAlO2The sodium hydroxide solution, the amount added and other steps were the same as in example 1.
Example 2
The high nickel ternary material-sintering powder in the example 1 is changed into LiNi0.90Co0.05Mn0.05O2The procedure of burning the powder, washing with water, centrifuging and vacuum drying with coulter was the same as in example 1. Then, the dried powder is placed in a muffle furnace, and is heated to 650 ℃ in an oxygen atmosphere for heat preservation for 5 hours. Finally, naturally cooling to room temperature to obtain Al with low residual alkali and uniformly coated surface2O3And TiO2LiNi of (2)0.90Co0.05Mn0.05O2。
Example 3
The high nickel ternary material-sintering powder in the example 1 is changed into LiNi0.65Co0.20Mn0.15O2The procedure of burning the powder, washing with water, centrifugal drying and coulter vacuum drying in this order was the same as in example 1. And then, placing the dried high-nickel ternary material in a muffle furnace, and heating to 700 ℃ in an air atmosphere for heat preservation for 5 hours. Finally, naturally cooling to room temperature to obtain the product with low residual alkali and uniform surfaceCoated with Al2O3And TiO2LiNi of (2)0.65Co0.20Mn0.15O2。
Example 4
Pouring 50kg of deionized water into a washing kettle with polytetrafluoroethylene as a lining, adding a first additive consisting of a lithium chlorate solution into the deionized water, uniformly stirring, and then mixing the high-nickel ternary material first-fired powder and the deionized water according to a solid-to-liquid ratio of 1: 0.5 addition of LiNi0.85Co0.10Mn0.05O2Stirring the powder at high speed to form uniform first slurry, wherein in the first additive, Li+The effective ion content is 0.001 wt%, and the addition amount of the first additive is 3 wt% of the mass of the added high-nickel ternary material calcined powder.
According to TiO aspect2+:Al3+:AlO2 -TiOSO is simultaneously added dropwise to the first slurry at a molar ratio of 1:1:5 to an effective ion content of 0.02 wt%4Sulfuric acid solution, 0.02 wt% Al2(SO4)3Sulfuric acid solution and 0.1wt% NaAlO2Sodium hydroxide solution, TiOSO4The amount of the sulfuric acid solution added was LiNi0.85Co0.10Mn0.05O2And 1% of the powder, controlling the dropping time to be 10min, and continuing to stir at a high speed for 5min after the dropping is finished to obtain a second slurry.
And centrifugally separating the second slurry, and then placing the second slurry in coulter drying equipment for vacuum drying, wherein the rotating speed of the coulter is 20r/min, the drying temperature is 150 ℃, the drying time is 10h, and the vacuum degree is set to be-0.1 MPa. Placing the dried material in a muffle furnace, heating to 700 ℃ in an oxygen environment, preserving heat for 7h, and naturally cooling to room temperature to obtain the coated TiO2And Al2O3LiNi of (2)0.85Co0.10Mn0.05O2A high nickel ternary material.
Example 5
Pouring 50kg of deionized water into a washing kettle with polytetrafluoroethylene as a lining, adding a first additive consisting of a lithium nitrate solution into the deionized water, uniformly stirring, and solidifying high-nickel ternary material calcined powder and the deionized waterThe liquid ratio is 1:5 addition of LiNi0.85Co0.10Mn0.05O2Stirring the powder at high speed to form uniform first slurry, wherein in the first additive, Li+The effective ion content is 0.1wt%, and the addition amount of the first additive is 10 wt% of the mass of the added high-nickel ternary material calcined powder.
According to TiO aspect2+:Al3+:AlO2 -The first slurry was simultaneously added dropwise with TiOSO in an amount of 0.001 wt% of available ion content at a mass ratio of 1:1:54Sulfuric acid solution, 0.001 wt% Al2(SO4)3Sulfuric acid solution and 0.005 wt% NaAlO2Sodium hydroxide solution, TiOSO4The amount of the sulfuric acid solution added was LiNi0.85Co0.10Mn0.05O2And 2% of the powder, controlling the dropping time to be 3min, and continuing to stir at a high speed for 5min after the dropping is finished to obtain a second slurry.
And centrifugally separating the second slurry, and then placing the second slurry in coulter drying equipment for vacuum drying, wherein the rotating speed of the coulter is 10r/min, the drying temperature is 120 ℃, the drying time is 3h, and the vacuum degree is set to be-0.04 MPa. Placing the dried material in a muffle furnace, heating to 500 ℃ in an oxygen environment, preserving heat for 3h, and naturally cooling to room temperature to obtain the coated TiO2And Al2O3LiNi of (2)0.85Co0.10Mn0.05O2A high nickel ternary material.
Test example
1. Transmission electron microscope and scanning electron microscope characterization are carried out on the high-nickel ternary material in the embodiment 1, the results are shown in figures 1 and 2, and TiO can be observed through figures 1 and 22And Al2O3Is uniformly coated on LiNi0.85Co0.10Mn0..05O2The surface of the material.
Meanwhile, the high-nickel ternary material in comparative example 1 is characterized by a scanning electron microscope, and as shown in fig. 3, nanoparticles with uneven sizes are found on the surface of the material, and mainly Al2O3And TiO2Non-uniform dispersion. And black substances exist on the surface of the material, which indicates that a large amount of residual alkali exists on the surface of the product。
2. The surface residual alkali of the high-nickel ternary cathode material in the embodiment 1, the comparative example 2 and the comparative example 3 is respectively tested, and the result is shown in table 1, wherein the residual alkali testing method is an enterprise self-made method, and the specific testing steps are as follows:
(1) preparing a 0.01M standard hydrochloric acid solution: 0.0220g of dried sodium carbonate (d) were weighed accurately into a 250mL volumetric flask, 100mL of deionized water were added, mixed well, 3 drops of methyl orange indicator were added, titrated with hydrochloric acid (a) until the color changed from yellow to orange, the volume of hydrochloric acid consumed by the titration was recorded, and the above procedure was repeated twice.
(2) Sample treatment: accurately weighing 5g of sample to be detected in a 250mL conical flask, adding 100mL of deionized water, covering a bottle stopper, oscillating for half an hour, and performing dry filtration to obtain filtrate for later use.
(3) Determination of the total basicity: transferring 10mL of filtrate into a 250mL conical flask, adding 2 drops of methyl red-methylene blue (c), titrating with a hydrochloric acid standard solution (a) under continuous oscillation until the end point changes from green to purple, recording the volume of the consumed hydrochloric acid, and determining the total volume V of the carbonate and hydroxyl consumed hydrochloric acid1。
(4) Determination of hydroxyl: transferring 10mL of filtrate into a 250mL conical flask, adding 5mL of barium chloride (e) to precipitate carbonate and sulfate, adding 2 drops of phenolphthalein indicator, if the filtrate is red, indicating that the filtrate contains hydroxide radicals, and if the filtrate is not red, indicating that no hydroxide radicals exist, titrating with a hydrochloric acid standard solution (a) under sufficient oscillation until the red color disappears, and recording the volume V of the consumed hydrochloric acid2。
(5) Calculation of analysis results:
LiOH and Li were calculated as follows2CO3The content of (A):
Figure BDA0002713259140000101
Figure BDA0002713259140000102
in the formula: v1Volume of hydrochloric acid consumed for titration of total alkalinity (mL), V2Titration of the volume of hydroxide consuming hydrochloric acid (mL), V3The volume (mL) of the hydroxide filtrate, the m-weight (g) and the C-hydrochloric acid concentration (moL/L) were measured by fractionation.
3. The high-nickel ternary material, the conductive agent SP and the binder PVDF in the embodiments 1, 2 and 3 are prepared into a pole piece by taking NMP as a solvent according to the mass ratio of 97.5:1:1.5, the pole piece is coated on a carbon-coated aluminum foil, the carbon-coated aluminum foil is dried for 5 hours at 100 ℃, and the positive pole piece is compacted on a roller press to prepare the positive pole piece.
The button cell is assembled by using a metal lithium sheet as a negative electrode, a 1M LiPF6 solution as an electrolyte and a cell gard2300 as a diaphragm and the positive electrode sheet respectively, and the button cell is charged and discharged at a cut-off voltage of 2.8-4.3V and a multiplying factor of 0.2C, and the result is shown in Table 1 and figure 4.
TABLE 1 residual alkali content and electrochemical Performance test of lithium ion batteries in examples and comparative examples
Figure BDA0002713259140000103
As can be seen from Table 1, in example 1, the first charge-discharge specific capacities were 234.5 and 204.0mAh g, respectively-1The first coulombic efficiency was 87.0%, which showed excellent electrochemical performance, further, as shown in fig. 4. The specific discharge capacity of the material 1C is 192.1mAh g-1And the capacity retention rate reaches 98.5% after 50 cycles, which shows that the lithium ion battery prepared from the high-nickel ternary material in example 1 has excellent electrochemical performance.
Further analysis shows that compared with the example 1, the comparative example 1 has the advantages that the discharge capacity and the first effect of the product are reduced, which are related to the higher residual alkali content on the surface of the high-nickel ternary material, and mainly because the high residual alkali content increases the occurrence of side reaction of the electrolyte, lithium salt is lost, the material capacity and the first effect are reduced, and the cycle performance of the material is deteriorated; comparative example 2 the capacity and first efficiency of the lithium ion battery were slightly reduced compared to example 1, but increased compared to comparative example 1, mainly because the water washing reduced the high nickel trisThe residual alkali content on the surface of the element material reduces the occurrence of side reaction of the electrolyte and the loss of lithium salt. But due to the presence of the material matrix Li during the water washing process+Excessive loss, resulting in a reduction in the cycle performance of the product compared to both example 1 and comparative example 1; table 1 shows that the residual alkali content of comparative example 3 is basically the same as that of example 1 and comparative example 2 and is far lower than that of comparative example 1, which shows that the residual alkali content on the surface of the high-nickel ternary material can be effectively reduced by water washing, the battery capacity and the first effect are almost not changed compared with example 1, but the 1C and 50-week cycle capacity retention rate is obviously reduced mainly because Li added in the water washing process of example 1+Can inhibit material matrix Li+Excessive precipitation and stable matrix structure, so that the capacity and the first effect are kept stable, but the surface of the high-nickel ternary material in the comparative example 3 is not coated with Al2O3And TiO2The contact area between the material and the electrolyte is increased, side reactions are increased, and the cycle performance is reduced.
The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.

Claims (10)

1. A surface modification method of a high-nickel ternary material is characterized by comprising the following steps:
adding a first additive and high-nickel ternary material calcined powder into deionized water, and uniformly stirring to obtain a first slurry, wherein the first additive is cation Li+Is soluble inA salt, wherein the soluble salt is at least one selected from sulfate, nitrate, phosphate and chloride;
simultaneously dripping a second additive, a third additive and a fourth additive into the first slurry, and continuously stirring to obtain a second slurry after dripping is finished, wherein the second additive is TiOSO4An acidic solution, and the third additive is Al2(SO4)3The fourth additive is NaAlO2An alkaline solution;
and centrifuging the second slurry, dynamically rotating, drying and calcining to obtain the surface-modified high-nickel ternary material.
2. The surface modification method of claim 1, wherein the high nickel ternary material-calcined powder has a chemical formula composition of LiNixCoyM1-x-yO2Wherein M is at least one of Mn, Al, Zr, Ti and Mg, x is more than or equal to 0.60, and y is less than or equal to 0.20.
3. The surface modification method of claim 1, wherein the first additive comprises a cation Li+The effective ion content of the high-nickel ternary material is 0.001-0.1wt%, the addition amount of the first additive is 3-10% of the mass of the high-nickel ternary material calcined powder, and the solid-liquid mass ratio of the high-nickel ternary material calcined powder to the deionized water is 1: 0.5-5.
4. The surface modification method of claim 1, wherein the second additive is added in an amount of 1-10% by mass of the high-nickel ternary material calcined powder, and the second additive, the third additive and the fourth additive are in accordance with TiO2+ : Al3+ : AlO2 -And the molar ratio of 1:1:5, wherein the effective ion content in the second additive, the third additive and the fourth additive is 0.001-0.1 wt%.
5. The surface modification method of claim 1, wherein the TiOSO is4Acid solution, Al2(SO4)3The acid solutions in the acid solutions are respectively and independently selected from at least one of sulfuric acid solution, hydrochloric acid solution, acetic acid solution, nitric acid solution and citric acid solution;
the NaAlO2The alkaline solution in the alkaline solution is at least one selected from sodium hydroxide solution, potassium hydroxide solution, lithium hydroxide solution and ammonia water solution.
6. The surface modification method according to claim 1, wherein the dropping time of the second additive, the third additive and the fourth additive is controlled to be 3 to 10 min.
7. The surface modification method of claim 1, wherein the dynamic rotary drying is performed by vacuum coulter, the rotation speed is maintained at 3-20r/min, the drying temperature is 120 ℃ and 150 ℃, the drying time is 3-10h, and the vacuum degree is maintained at-0.04 to-0.1 MPa.
8. The surface modification method of claim 1, wherein the sintering temperature of the calcination is 500-700 ℃ and the holding time is 3-7 h.
9. A high nickel ternary material, characterized in that it is obtained by surface modification by the surface modification method according to any one of claims 1 to 8.
10. A lithium ion battery comprising the high nickel ternary material of claim 9.
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