CN107275633B - Gradient fluorine-doped ternary cathode material with low lattice stress and preparation method thereof - Google Patents

Gradient fluorine-doped ternary cathode material with low lattice stress and preparation method thereof Download PDF

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CN107275633B
CN107275633B CN201710446261.XA CN201710446261A CN107275633B CN 107275633 B CN107275633 B CN 107275633B CN 201710446261 A CN201710446261 A CN 201710446261A CN 107275633 B CN107275633 B CN 107275633B
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aqueous solution
fluoride
mixed metal
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metal salt
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CN107275633A (en
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杜春雨
徐晟�
徐星
尹鸽平
左朋建
程新群
马玉林
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Harbin Institute of Technology
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • 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
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

A gradient fluorine-doped ternary cathode material with low lattice stress and a preparation method thereof. The invention belongs to the field of lithium ion batteries, and particularly relates to a gradient fluorine-doped ternary cathode material with low lattice stress and a preparation method thereof. The invention aims to solve the problems that the lattice stress is generated due to the change of the proportion of transition metal elements in the oxide anode material of the lithium ion battery at present, so that the lattice stress of the oxide anode material of the lithium ion battery is higher, and the cycle stability and the rate capability of the electrode material are influenced. The method comprises the following steps: firstly, preparing a mixed metal salt water solution; secondly, preparing a precipitator aqueous solution; thirdly, preparing a complexing agent for dissolving in water; fourthly, preparing a fluoride aqueous solution; fifthly, preparing a precursor material; sixthly, cooling; seventhly, the method comprises the following steps: preparing the gradient fluorine-doped ternary cathode material. The content change of Ni and F in the gradient fluorine-doped ternary cathode material is in reverse gradient change, the lattice stress is reduced, and the cycle performance and the rate capability are improved.

Description

Gradient fluorine-doped ternary cathode material with low lattice stress and preparation method thereof
Technical Field
The invention belongs to the field of lithium ion batteries, and particularly relates to a gradient fluorine-doped ternary cathode material with low lattice stress and a preparation method thereof.
Background
Since the commercialization of lithium ion batteries in the 90 s of the 20 th century, lithium ion batteries have rapidly become the most important and most widely used secondary batteries. Through the development of many years, the lithium ion battery is widely applied to various small portable electronic products and electric tools, and is gradually applied to the new energy automobile market in a large amount along with the recent increase of attention on energy in various countries in the world. The anode material is one of the key materials for manufacturing the lithium ion battery, and because the specific capacity of the common anode material is obviously lower than that of the cathode material, the performance of the anode material directly influences various indexes of the final battery. Therefore, it is extremely important to develop a positive electrode material.
Lithium cobaltate (LiCoO)2) The lithium ion battery cathode material is a cathode material used in the first commercial lithium ion battery of Sony company, and still is a mainstream material in the lithium ion battery market at present. However, cobalt has high toxicity, high price and excessive Li desorption+The structural instability due to oxygen layer repulsion is exacerbated, creating cost and safety issues, and better alternative materials are constantly being sought. The voltage of the layered lithium manganate is high, the cost is low, but the capacity retention rate is not ideal due to John-Teller effect in the circulation process. And the application of the lithium iron phosphate is limited due to the problems of large polarization, quick reduction of reversible capacity, poor conductivity and the like under high multiplying power.
In contrast, lithium nickel cobalt manganese oxide ternary material (LiNi)xCoyMnzO2) With LiCoO2Similar single phase layered structure. Ternary metal oxide materials incorporating LiCoO based on the synergistic effects between transition metals2Good rate capability and LiNiO2High capacity, and due to Mn4+The structural stability obtained. In the material, Ni is a main active substance, and the content of Ni is positively correlated with the capacity of the positive electrode material; therefore, the development of high nickel ternary materials has become a development trend of ternary cathode materials of lithium ion batteries.
However, the high nickel ternary material has high capacity due to high nickel content, and the structure and thermal stability of the high nickel material in a lithium-removed state are not ideal, and in addition, with the increase of the nickel content, a serious lithium-nickel mixed-discharging phenomenon is caused, so that the cycle performance of the material is poor. Therefore, researchers develop the ternary material with gradient change from inside to outside, and the gradient material has the advantages of good material cycle performance and high specific capacity due to the gradient change of components from inside to outside.
However, the lattice stress exists in the high nickel gradient ternary cathode material with different metal proportions due to different lattice parameters, so that the material is easy to pulverize and break in the charge-discharge cycle process, the stress resistance strength of the electrode material is further influenced, and the cycle stability and the rate capability of the material are reduced, so that finding a simple method for improving the stress resistance of the high nickel gradient ternary material has important significance.
Disclosure of Invention
The invention aims to solve the problems that the lattice stress is generated due to the change of the proportion of transition metal elements in the oxide anode material of a lithium ion battery at present, so that the lattice stress of the oxide anode material of the lithium ion battery is higher, and the cycling stability and the rate capability of an electrode material are influenced, and provides a gradient fluorine-doped ternary anode material with low lattice stress and a preparation method thereof.
The chemical formula of the gradient fluorine-doped ternary cathode material with low lattice stress is LiNixCoyMnzM1-x-y-zO2-nFn(ii) a Wherein the content x of Ni is reduced in a gradient manner from inside to outside, the content n of F is increased in a gradient manner from inside to outside, x is more than 0 and less than or equal to 1, y is more than 0 and less than or equal to 1, z is more than 0 and less than or equal to 1, and 0<x+y+z≤1，0<n≤0.15。
The preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress is carried out according to the following steps:
①, mixing nickel salt, cobalt salt, manganese salt and M salt according to a molar ratio to prepare a mixed metal salt aqueous solution A, wherein the concentration of the mixed metal salt in the mixed metal salt aqueous solution A is 0.01-20 mol/L, and the molar ratio of nickel element, cobalt element, manganese element and M element in the mixed metal salt aqueous solution A is nickel element, cobalt element, manganese element and M element x1:y1:z1:(1-x1-y1-z1) (ii) a Wherein x is more than or equal to 01≤1，0≤y1≤1，0≤z1≤1，0<x1+y1+z 1② mixing nickel salt, cobalt salt, manganese salt and M salt according to the mol ratio to prepare mixed metal salt water solution B, wherein the concentration of the mixed metal salt in the mixed metal salt water solution B is 0.01-20 mol/L, and the mol ratio of nickel element, cobalt element, manganese element and M element in the mixed metal salt water solution B is that nickel element, cobalt element and M element are x2:y2:z2:(1-x2-y2-z2) (ii) a Wherein x is more than or equal to 02≤1，0≤y2≤1，0≤z2≤1，0<x2+y2+z2≤1、x2:y2:z2:(1-x2-y2-z2)≠x1:y1:z1:(1-x1-y1-z1) And x1And x2Is not 0 and y simultaneously1And y2Is not 0 and z simultaneously1And z2Not simultaneously 0;
secondly, preparing a precipitant aqueous solution: mixing a precipitator with water to prepare a precipitator aqueous solution with the concentration of 0.01-20 mol/L;
preparing a complexing agent aqueous solution, wherein ① the complexing agent is mixed with water to prepare a complexing agent aqueous solution A, the concentration of the complexing agent in the complexing agent aqueous solution A is 0.01-20 mol/L, ② the complexing agent is mixed with water to prepare a complexing agent aqueous solution B, and the concentration of the complexing agent in the complexing agent aqueous solution B is 0.01-10 mol/L;
fourthly, preparing a fluoride aqueous solution, ① mixing fluoride with water to prepare a fluoride aqueous solution A, wherein the concentration of the fluoride in the fluoride aqueous solution A is 0.001-2 mol/L, ② mixing the fluoride with water to prepare a fluoride aqueous solution B, and the concentration of the fluoride in the fluoride aqueous solution B is 0-2 mol/L;
①, adding a complexing agent aqueous solution B in the third step into a continuous stirring liquid phase reactor to serve as a reaction base solution, ②, then, under the conditions that an inert atmosphere, the pH value is 4-14, the temperature is kept at 10-85 ℃ and the rotating speed is 600-1000 r/min, continuously injecting a mixed metal saline solution A, a precipitator aqueous solution, a complexing agent aqueous solution A and a fluoride aqueous solution A as first-stage feeding materials into the continuous stirring liquid phase reactor respectively, injecting the mixed metal saline solution B and the fluoride aqueous solution B as second-stage feeding materials into the mixed metal saline solution A and the fluoride aqueous solution A respectively while injecting the first-stage feeding materials, continuously injecting the first-stage feeding materials and the second-stage feeding materials into the continuous stirring liquid phase reactor, wherein the adding of the first-stage feeding materials and the second-stage feeding materials lasts for the whole preparation process, when the solid-liquid mass ratio in the continuous stirring liquid phase reactor is 1/40-1/5 during the reaction of ③, the rotating speed is reduced from 600 r/min-1000 r/min, the reduction range is 200 r/300 r/min, the reaction is carried out for 0.5-2 h, ④ is opened to start overflowing, the time of the adding of the overflow pipe is 357, the continuous stirring liquid phase solution, the reaction is carried out, and the step of the step is repeated, the step of the step;
in the step five ①, the volume of the complexing agent aqueous solution B is 10-80% of the volume of the continuous stirring liquid phase reactor;
the feeding rate ratio of the four substances of the primary feeding in the step five ② is that the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(OH)2-nFnFeeding rate ratio of the mixed metal salt aqueous solution A to the precipitant aqueous solution to the complexing agent aqueous solution A to the fluoride aqueous solution A is 1:2:1: 1; the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(CO3)1-0.5nFnFeeding rate ratio of the mixed metal salt aqueous solution A to the precipitant aqueous solution to the complexing agent aqueous solution A to the fluoride aqueous solution A is 1:1:1: 1;
the feeding rates of the mixed metal brine solution B and the mixed metal brine solution A in the step five ② are the same, and the feeding rates of the primary feeding fluoride aqueous solution B and the fluoride aqueous solution A are the same;
in the fifth step ②, the ratio of the total moles of complexing agent in the complexing agent aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-10.0: 1, the ratio of the moles of precipitant in the precipitant aqueous solution to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-4.0: 1, and the ratio of the total moles of fluoride in the fluoride aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.001-2.0: 1;
sixthly, cooling: stirring for 1-3 h under the condition that the rotating speed is 500-1000 r/min to reduce the temperature of the continuous stirring liquid phase reactor to room temperature to obtain precursor material NixCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1- 0.5nFn；
Seventhly, preparing the gradient fluorine-doped ternary cathode material: firstly, obtaining a precursor material Ni in the sixth stepxCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1-0.5nFnVacuum drying, pre-sintering for 6-10 h at 700-800 ℃ in an oxygen atmosphere, and then mixing the pre-sintered precursor material with a lithium source according to a molar ratio of 1: (1-1.25), uniformly mixing, sintering for 1-45 h at 500-1000 ℃ in pure oxygen or air atmosphere, and sieving to obtain the gradient fluorine-doped ternary cathode material LiNi with low lattice stressxCoyMnzM1-x-y-zO2-nFn。
The invention has the beneficial effects that:
1. the invention controls the gradient fluorine-doped ternary cathode material LiNi of the lithium ion batteryxCoyMnzM1-x-y-zO2-nFnThe content of Ni and F is changed, so that the content x of Ni and the content n of F are in reverse gradient change, the increase of the content of Ni element can reduce lattice parameter in a certain range, the increase of F element can increase lattice parameter, make up the lattice parameter reduction caused by the decrease of the content of Ni, and make up the gradient fluorine doped ternary gradient materialThe lattice parameters inside and outside the material are consistent, the lattice is matched, and the lattice stress of the prepared oxide anode material is effectively reduced, so that the internal stress is small. Therefore, the structural stability of the anode material in the charging and discharging process can be improved, and the cycle performance and the rate capability of the anode material are improved.
2. According to the invention, a two-stage feeding mode is adopted, and the characteristic of uniform stirring by a coprecipitation method is utilized, so that uniform gradient change of metal elements and F elements is realized, and the accuracy and controllability of the chemical composition of the material are ensured.
3. The gradient F-doped ternary cathode material prepared by the invention utilizes the fluxing agent characteristic of metal fluoride to reduce the solid phase sintering temperature of the ternary gradient cathode material and save more energy.
4. The preparation process is simple, the material cost is low, and the method is suitable for industrial production.
Drawings
FIG. 1 shows the precursor material Ni obtained in the first step and the second step of the experiment0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075SEM picture of (1);
FIG. 2 is a schematic diagram showing a lattice structure comparison of the ternary cathode material before and after gradient fluorine doping in test one;
FIG. 3 is a graph showing that a gradient fluorine-doped ternary oxide positive electrode material LiNi with low lattice stress is prepared in the first experiment0.481Co0.193Mn0.289O1.925F0.075SEM picture of (1);
FIG. 4 is a graph showing experiment-prepared gradient fluorine-doped ternary oxide positive electrode material LiNi with low lattice stress0.481Co0.193Mn0.289O1.925F0.075XRD pattern of (a);
FIG. 5 is a graph showing the experimental results of a gradient fluorine-doped ternary oxide positive electrode material LiNi with low lattice stress prepared0.481Co0.193Mn0.289O1.925F0.075The first charge-discharge curve chart under the multiplying power of 0.1C;
FIG. 6 is a graph showing that a gradient fluorine-doped ternary oxide positive electrode material LiNi with low lattice stress is prepared by experiment one0.481Co0.193Mn0.289O1.925F0.075The rate performance curve of (1);
FIG. 7 is a graph showing experiment-preparation of gradient fluorine-doped ternary cathode material LiNi with low lattice stress0.481Co0.193Mn0.289O1.925F0.075And a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2The comparative cycle performance curve under the 1C multiplying power of (1);
FIG. 8 is a graph showing the experimental results of a gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared0.481Co0.193Mn0.289O1.925F0.075SEM images after 200 cycles at magnification of 1C;
FIG. 9 is a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2SEM images after 200 cycles at magnification of 1C.
Detailed Description
The first embodiment is as follows: the chemical formula of the gradient fluorine-doped ternary cathode material with low lattice stress of the embodiment is LiNixCoyMnzM1-x-y-zO2-nFn(ii) a Wherein the content x of Ni is reduced in a gradient manner from inside to outside, the content n of F is increased in a gradient manner from inside to outside, x is more than 0 and less than or equal to 1, y is more than 0 and less than or equal to 1, z is more than 0 and less than or equal to 1, and 0<x+y+z≤1，0<n≤0.15。
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the variation gradient of the content x of Ni and the variation gradient of the content n of F satisfy delta being more than or equal to 5x/ΔnLess than or equal to 7; wherein ΔxIs the difference in Ni content x at different distances from the center of the sphere, DeltanIs the difference in the content n of F at the position corresponding to the content x of Ni. Other steps and parameters are the same as those in the first embodiment.
The third concrete implementation mode: the present embodiment differs from the first or second embodiment in that: and M is one or a mixture of more of Li, Zr, Fe, Sm, Pr, Nb, Ga, Zn, Y, Mg, Al, Cr, Ca, Na, Ti, Cu, K, Sr, Mo, Ba, Ce, Sn, Sb, La and Bi. Other steps and parameters are the same as those in the first or second embodiment.
The fourth concrete implementation mode: the preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress is carried out according to the following steps:
①, mixing nickel salt, cobalt salt, manganese salt and M salt according to a molar ratio to prepare a mixed metal salt aqueous solution A, wherein the concentration of the mixed metal salt in the mixed metal salt aqueous solution A is 0.01-20 mol/L, and the molar ratio of nickel element, cobalt element, manganese element and M element in the mixed metal salt aqueous solution A is nickel element, cobalt element, manganese element and M element x1:y1:z1:(1-x1-y1-z1) (ii) a Wherein x is more than or equal to 01≤1，0≤y1≤1，0≤z1≤1，0<x1+y1+z 1② mixing nickel salt, cobalt salt, manganese salt and M salt according to the mol ratio to prepare mixed metal salt water solution B, wherein the concentration of the mixed metal salt in the mixed metal salt water solution B is 0.01-20 mol/L, and the mol ratio of nickel element, cobalt element, manganese element and M element in the mixed metal salt water solution B is that nickel element, cobalt element and M element are x2:y2:z2:(1-x2-y2-z2) (ii) a Wherein x is more than or equal to 02≤1，0≤y2≤1，0≤z2≤1，0<x2+y2+z2≤1、x2:y2:z2:(1-x2-y2-z2)≠x1:y1:z1:(1-x1-y1-z1) And x1And x2Is not 0 and y simultaneously1And y2Is not 0 and z simultaneously1And z2Not simultaneously 0;
secondly, preparing a precipitant aqueous solution: mixing a precipitator with water to prepare a precipitator aqueous solution with the concentration of 0.01-20 mol/L;
preparing a complexing agent aqueous solution, wherein ① the complexing agent is mixed with water to prepare a complexing agent aqueous solution A, the concentration of the complexing agent in the complexing agent aqueous solution A is 0.01-20 mol/L, ② the complexing agent is mixed with water to prepare a complexing agent aqueous solution B, and the concentration of the complexing agent in the complexing agent aqueous solution B is 0.01-10 mol/L;
fourthly, preparing a fluoride aqueous solution, ① mixing fluoride with water to prepare a fluoride aqueous solution A, wherein the concentration of the fluoride in the fluoride aqueous solution A is 0.001-2 mol/L, ② mixing the fluoride with water to prepare a fluoride aqueous solution B, and the concentration of the fluoride in the fluoride aqueous solution B is 0-2 mol/L;
①, adding a complexing agent aqueous solution B in the third step into a continuous stirring liquid phase reactor to serve as a reaction base solution, ②, then, under the conditions that an inert atmosphere, the pH value is 4-14, the temperature is kept at 10-85 ℃ and the rotating speed is 600-1000 r/min, continuously injecting a mixed metal saline solution A, a precipitator aqueous solution, a complexing agent aqueous solution A and a fluoride aqueous solution A as first-stage feeding materials into the continuous stirring liquid phase reactor respectively, injecting the mixed metal saline solution B and the fluoride aqueous solution B as second-stage feeding materials into the mixed metal saline solution A and the fluoride aqueous solution A respectively while injecting the first-stage feeding materials, continuously injecting the first-stage feeding materials and the second-stage feeding materials into the continuous stirring liquid phase reactor, wherein the adding of the first-stage feeding materials and the second-stage feeding materials lasts for the whole preparation process, when the solid-liquid mass ratio in the continuous stirring liquid phase reactor is 1/40-1/5 during the reaction of ③, the rotating speed is reduced from 600 r/min-1000 r/min, the reduction range is 200 r/300 r/min, the reaction is carried out for 0.5-2 h, ④ is opened to start overflowing, the time of the adding of the overflow pipe is 357, the continuous stirring liquid phase solution, the reaction is carried out, and the step of the step is repeated, the step of the step;
in the step five ①, the volume of the complexing agent aqueous solution B is 10-80% of the volume of the continuous stirring liquid phase reactor;
the feeding rate ratio of the four substances of the primary feeding in the step five ② is that the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(OH)2-nFnMixed aqueous metal salt solution A, aqueous precipitant solution, aqueous complexing agent solution A and fluorineThe feeding rate ratio of the compound aqueous solution A is 1:2:1: 1; the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(CO3)1-0.5nFnFeeding rate ratio of the mixed metal salt aqueous solution A to the precipitant aqueous solution to the complexing agent aqueous solution A to the fluoride aqueous solution A is 1:1:1: 1;
the feeding rates of the mixed metal brine solution B and the mixed metal brine solution A in the step five ② are the same, and the feeding rates of the primary feeding fluoride aqueous solution B and the fluoride aqueous solution A are the same;
in the fifth step ②, the ratio of the total moles of complexing agent in the complexing agent aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-10.0: 1, the ratio of the moles of precipitant in the precipitant aqueous solution to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-4.0: 1, and the ratio of the total moles of fluoride in the fluoride aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.001-2.0: 1;
sixthly, cooling: stirring for 1-3 h under the condition that the rotating speed is 500-1000 r/min to reduce the temperature of the continuous stirring liquid phase reactor to room temperature to obtain precursor material NixCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1- 0.5nFn；
Seventhly, preparing the gradient fluorine-doped ternary cathode material: firstly, obtaining a precursor material Ni in the sixth stepxCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1-0.5nFnVacuum drying, pre-sintering for 6-10 h at 700-800 ℃ in an oxygen atmosphere, and then mixing the pre-sintered precursor material with a lithium source according to a molar ratio of 1: (1-1.25), uniformly mixing, sintering for 1-45 h at 500-1000 ℃ in pure oxygen or air atmosphere, and sieving to obtain the gradient fluorine-doped ternary cathode material LiNi with low lattice stressxCoyMnzM1-x-y-zO2-nFn。
The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: in the first step, the nickel salt is one or a mixture of more of nickel sulfate, nickel nitrate, nickel acetate and nickel chloride. Other steps and parameters are the same as those in the fourth embodiment.
The sixth specific implementation mode: the present embodiment is different from the fourth or fifth embodiment in that: the cobalt salt is one or a mixture of more of cobalt sulfate, cobalt nitrate, cobalt acetate and cobalt chloride. Other steps and parameters are the same as those in one of the fourth or fifth embodiments.
The seventh embodiment: this embodiment differs from one of the fourth to sixth embodiments in that: the manganese salt is one or a mixture of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride. Other steps and parameters are the same as those in one of the fourth to sixth embodiments.
The specific implementation mode is eight: this embodiment is different from one of the fourth to seventh embodiments in that: in the step one, the M salt is one or a mixture of more of soluble sulfate, soluble nitrate, soluble acetate, soluble chloride, soluble citrate and soluble alkoxide; wherein M is one or a mixture of more of Li, Zr, Fe, Sm, Pr, Nb, Ga, Zn, Y, Mg, Al, Cr, Ca, Na, Ti, Cu, K, Sr, Mo, Ba, Ce, Sn, Sb, La and Bi. Other steps and parameters are the same as those of one of the fourth to seventh embodiments.
The specific implementation method nine: this embodiment is different from the fourth to eighth embodiment in that: in the second step, the precursor material is NixCoyMnzM1-x-y-z(OH)2-nFnThe precipitant is one or a mixture of several of sodium hydroxide, potassium hydroxide and lithium hydroxide. Other steps and parameters are the same as those in one of the fourth to eighth embodiments.
The detailed implementation mode is ten: this embodiment is different from one of the fourth to ninth embodiments in that: in the second stepThe precursor material is NixCoyMnzM1-x-y-z(CO3)1-0.5nFnThe precipitator is one or a mixture of more of sodium carbonate, potassium carbonate and lithium carbonate. Other steps and parameters are the same as those in one of the fourth to ninth embodiments.
The concrete implementation mode eleven: the present embodiment is different from one of the fourth to tenth embodiments in that: in the third step, the complexing agent is one or a mixture of more of ammonia water, ammonium chloride, ammonium fluoride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium acetate, EDTA, ammonium citrate, ethylenediamine, acetic acid, sodium fluoride, tartaric acid, maleic acid, succinic acid, citric acid and malonic acid. Other steps and parameters are the same as those in one of the fourth to tenth embodiments.
The specific implementation mode twelve: this embodiment is different from one of the fourth to eleventh embodiments in that: the fluoride in the fourth step is one or a mixture of sodium fluoride, potassium fluoride and ammonium chloride. Other steps and parameters are the same as those of one of the fourth to eleventh embodiments.
The specific implementation mode is thirteen: this embodiment is different from the fourth to twelfth embodiment in that: and in the seventh step, the lithium source is one or a mixture of several of lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, lithium fluoride, lithium oxalate, lithium phosphate, lithium hydrogen phosphate and lithium carbonate. Wherein other steps and parameters are the same as those of the fourth to twelfth embodiments.
The following experiments were conducted to verify the effects of the present invention
The first test is that the preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress is carried out according to the following steps:
①, mixing nickel sulfate, cobalt sulfate, manganese sulfate and lithium sulfate according to a molar ratio to prepare a mixed metal salt water solution A, wherein the concentration of the mixed metal salt in the mixed metal salt water solution A is 2mol/L, the molar ratio of nickel element to cobalt element to manganese element to lithium element in the mixed metal salt water solution A is 2.7: 0.9: 5.4: 1, ② mixing nickel sulfate, cobalt sulfate, manganese sulfate and lithium sulfate according to a molar ratio to prepare a mixed metal salt water solution B, the concentration of the mixed metal salt in the mixed metal salt water solution B is 2mol/L, and the molar ratio of nickel element to cobalt element to manganese element to lithium element in the mixed metal salt water solution B is 3: 3: 3: 1;
secondly, preparing a precipitant aqueous solution: mixing sodium hydroxide with water to prepare a precipitant aqueous solution with the concentration of the sodium hydroxide of 2 mol/L;
thirdly, preparing a complexing agent aqueous solution, ① mixing ammonia water with water to prepare a complexing agent aqueous solution A, wherein the concentration of the ammonia water in the complexing agent aqueous solution A is 2.8mol/L, ② mixing the ammonia water with water to prepare a complexing agent aqueous solution B, and the concentration of the ammonia water in the complexing agent aqueous solution B is 0.3 mol/L;
fourthly, preparing a fluoride aqueous solution, ① mixing ammonium fluoride with water to prepare a fluoride aqueous solution A, wherein the concentration of the ammonium fluoride in the fluoride aqueous solution A is 0.01mol/L, ② mixing the ammonium fluoride with water to prepare a fluoride aqueous solution B, and the concentration of the ammonium fluoride in the fluoride aqueous solution B is 0.15 mol/L;
①, adding the complexing agent aqueous solution B in the third step into a continuous stirring liquid phase reactor to be used as a reaction base solution, ②, then, under the conditions of inert atmosphere, pH value of 10 +/-0.3, constant temperature of 60 ℃ and rotation speed of 900r/min, continuously injecting the mixed metal salt aqueous solution A, the precipitator aqueous solution, the complexing agent aqueous solution A and the fluoride aqueous solution A as first-stage feeding materials into the continuous stirring liquid phase reactor respectively, injecting the first-stage feeding materials and simultaneously injecting the mixed metal salt aqueous solution B and the fluoride aqueous solution B as second-stage feeding materials into the mixed metal salt aqueous solution A and the fluoride aqueous solution A respectively, wherein the adding of the first-stage feeding materials and the second-stage feeding materials lasts for the whole preparation process, ③, after the reaction is carried out for 1h, the rotation speed is adjusted downwards from 900r/min, the adjustment range is 300r/min, the reaction is carried out for 2h at the rotation speed after the adjustment downwards, ④ is opened to start overflowing, the overflow pipe is the feeding amount within 2h of the step ③, the solution amount in the continuous stirring liquid phase reactor is recovered to the solution amount at the start time of the step 2, ⑤ is repeated, the step 387, the total feeding time of the first-stage feeding;
in the step five ①, the volume of the complexing agent aqueous solution B is 72 percent of the volume of the continuous stirring liquid phase reactor, wherein the volume of the complexing agent aqueous solution B is 720mL, and the volume of the continuous stirring liquid phase reactor is 1L;
feeding rate ratios of four materials of the primary feeding in the step five ② are that the feeding rate ratio of the mixed metal salt aqueous solution A, the precipitator aqueous solution, the complexing agent aqueous solution A and the fluoride aqueous solution A is 1:2:1: 1;
the feeding rates of the mixed metal brine solution B and the mixed metal brine solution A in the step five ② are the same, and the feeding rates of the primary feeding fluoride aqueous solution B and the fluoride aqueous solution A are the same;
sixthly, cooling: stirring for 3h under the condition that the rotating speed is 700r/min to ensure that the continuous stirring liquid phase reactor is cooled to room temperature to obtain precursor material Ni0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075；
Seventhly, preparing the gradient fluorine-doped ternary cathode material: firstly, obtaining a precursor material Ni in the sixth step0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075Vacuum drying, pre-sintering at 750 deg.C for 8 hr in oxygen atmosphere, and pre-sintering to obtain precursor Ni0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075And lithium carbonate according to a molar ratio of 1: 1.05, evenly mixing, sintering for 10 hours at the temperature of 850 ℃ in the pure oxygen atmosphere, and sieving to obtain the powder gradient fluorine-doped ternary cathode material LiNi with low lattice stress0.481Co0.193Mn0.289O1.925F0.075。
(I) pair of precursor material Ni obtained in the first step and the sixth step of experiment0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075SEM examination was carried out to obtain the precursor obtained in the sixth step of the experiment shown in FIG. 1Bulk material Ni0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075As can be seen from fig. 1, the average particle size of the precursor is 7 to 8 μm, and the precursor is spherical secondary particles in which a large number of flaky primary particles are tightly stacked, and the particle size is uniform.
(II) pair test of precursor material Ni obtained in the first step six0.481Co0.193Mn0.289Li0.075(OH)1.925F0.075The energy spectrum detection is carried out to obtain the energy spectrum parameters shown in the table 1, and it can be seen that the content of the Ni element is reduced from inside to outside, while the content of the F element is reversely changed and increased.
TABLE 1
(III) in the first test, a schematic diagram of the lattice structure comparison of the ternary cathode material before and after gradient fluorine doping is shown in FIG. 2; wherein a is a ternary gradient material without gradient F doping, 1 is a part with higher nickel content and has large lattice parameter; 2 is the part with lower nickel content and small lattice parameter; it can be seen from fig. 2 that since the radius of Ni particles is within a certain range, the decrease of the content of Ni element reduces the lattice parameter, and the lattices of the ternary gradient material are not matched, resulting in internal lattice stress. b is a gradient fluorine-doped ternary gradient material with low lattice stress, 3 is a part with high nickel content and low fluorine content, and 4 is a part with low nickel content and high fluorine content, wherein the content x of Ni and the content n of F are in reverse gradient change. Therefore, the structural stability of the anode material in the charging and discharging process can be improved, and the cycle performance and the rate capability of the anode material are improved.
(IV) for the gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared in the first experiment0.481Co0.19 3Mn0.289O1.925F0.075SEM detection is carried out to obtain the gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by the verification test I shown in figure 30.481Co0.193Mn0.289O1.925F0.075And the SEM image of the cathode material shows that the cathode material has an average particle size of 7-8 μm, is spherical secondary particles composed of primary particles closely stacked in a particle shape, and has uniform particle size from FIG. 3.
(V) for the gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared in the first experiment0.481Co0.19 3Mn0.289O1.925F0.075X-ray diffraction detection is carried out to obtain the gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by the first test shown in figure 40.481Co0.193Mn0.289O1.925F0.075XRD pattern of (a); wherein 1 is gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by experiment I0.481Co0.193Mn0.289O1.925F0.075From fig. 4, it can be seen that the positive electrode material has a standard layered structure, and no impurity phase exists, indicating that the material of the present invention has a good structure.
(VI) gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared in experiment I0.481Co0.19 3Mn0.289O1.925F0.075The charge-discharge performance of the lithium ion battery was tested to obtain the gradient fluorine-doped ternary positive electrode material LiNi with low lattice stress prepared by the first test shown in FIG. 50.481Co0.193Mn0.289O1.925F0.075The first charge-discharge curve under the multiplying power of 0.1C is shown in figure 5, the first charge-discharge curve is a typical ternary material charge-discharge curve, and the first charge capacity reaches 170mAh g-1The first efficiency is 85%, which shows that the first capacity and the coulombic efficiency of the material synthesized by the method are high.
(VII) gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared in experiment one0.481Co0.19 3Mn0.289O1.925F0.075The gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by the first test shown in figure 6 is obtained by detecting the rate capability0.481Co0.193Mn0.289O1.925F0.075The graph of the rate capability of the present invention can be seen from fig. 6, which shows that the present invention has a better rate capability.
(eight) pairs of gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared in experiment I0.481Co0.19 3Mn0.289O1.925F0.075And a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2The cycle performance was examined at 1C magnification to obtain a gradient fluorine doped ternary positive electrode material LiNi with low lattice stress prepared as test one shown in fig. 70.481Co0.193Mn0.289O1.925F0.075And a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2The comparative cycle performance curve under the 1C multiplying power of (1); wherein 1 is gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by experiment I0.481Co0.193Mn0.289O1.925F0.075And 2 is a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2(ii) a As can be seen from fig. 7, since the lattice stress is small, experiment one prepared gradient fluorine-doped ternary cathode material LiNi having low lattice stress0.481Co0.193Mn0.289O1.925F0.075Can keep stable structure, has excellent material cycle performance, and has capacity retention rate of 98.2 percent after 100 cycles. In contrast, a control-like gradient ternary positive electrode material, LiNi0.481Co0.193Mn0.289O2The cycle performance is poor, and after 100 cycles, the capacity retention rate is 91.6%.
(nine) pairs of gradient fluorine-doped gradient ternary cathode materials LiNi with low lattice stress prepared in experiment I0.481Co0.193Mn0.289O1.925F0.075And a control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O2The obtained material was subjected to scanning electron microscope detection after cycling 200 times at a magnification of 1C to obtain the gradient fluorine-doped ternary cathode material LiNi with low lattice stress prepared by experiment one shown in FIG. 80.481Co0.193Mn0.289O1.925F0.075SEM image after cycling 200 times at 1C magnification and control sample gradient ternary cathode material LiNi as shown in FIG. 90.481Co0.193Mn0.289O2SEM images after 200 cycles at 1C magnification. It can be seen that experiment one prepared gradient fluorine-doped ternary cathode material LiNi with low lattice stress0.481Co0.193Mn0.28 9O1.925F0.075After circulation, secondary particles formed by agglomeration of primary particles are still intact due to small lattice stress, and the control sample gradient ternary cathode material LiNi0.481Co0.193Mn0.289O1.925F0.075The secondary particles after the cycle are broken, and the primary particles burst the secondary particles due to the change in stress.
The second test is that the preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress is carried out according to the following steps:
①, mixing nickel sulfate, cobalt sulfate, manganese sulfate and lithium sulfate according to a molar ratio to prepare a mixed metal salt water solution A, wherein the concentration of the mixed metal salt in the mixed metal salt water solution A is 2mol/L, the molar ratio of nickel element to cobalt element to manganese element to lithium element in the mixed metal salt water solution A is 2.7: 0.9: 5.4: 1, ② mixing nickel sulfate, cobalt sulfate, manganese sulfate and lithium sulfate according to a molar ratio to prepare a mixed metal salt water solution B, the concentration of the mixed metal salt in the mixed metal salt water solution B is 2mol/L, and the molar ratio of nickel element to cobalt element to manganese element to lithium element in the mixed metal salt water solution B is 3: 3: 3: 1;
secondly, preparing a precipitant aqueous solution: mixing sodium carbonate with water to prepare a precipitant aqueous solution with the concentration of the sodium carbonate of 2 mol/L;
thirdly, preparing a complexing agent aqueous solution, ① mixing ammonia water with water to prepare a complexing agent aqueous solution A, wherein the concentration of the ammonia water in the complexing agent aqueous solution A is 2.8mol/L, ② mixing the ammonia water with water to prepare a complexing agent aqueous solution B, and the concentration of the ammonia water in the complexing agent aqueous solution B is 0.3 mol/L;
fourthly, preparing a fluoride aqueous solution, ① mixing ammonium fluoride with water to prepare a fluoride aqueous solution A, wherein the concentration of the ammonium fluoride in the fluoride aqueous solution A is 0.01mol/L, ② mixing the ammonium fluoride with water to prepare a fluoride aqueous solution B, and the concentration of the ammonium fluoride in the fluoride aqueous solution B is 0.15 mol/L;
①, adding the complexing agent aqueous solution B in the third step into a continuous stirring liquid phase reactor to be used as a reaction base solution, ②, then, under the conditions of inert atmosphere, pH value of 10 +/-0.3, constant temperature of 60 ℃ and rotation speed of 900r/min, continuously injecting the mixed metal salt aqueous solution A, the precipitator aqueous solution, the complexing agent aqueous solution A and the fluoride aqueous solution A as first-stage feeding materials into the continuous stirring liquid phase reactor respectively, injecting the first-stage feeding materials and simultaneously injecting the mixed metal salt aqueous solution B and the fluoride aqueous solution B as second-stage feeding materials into the mixed metal salt aqueous solution A and the fluoride aqueous solution A respectively, wherein the adding of the first-stage feeding materials and the second-stage feeding materials lasts for the whole preparation process, ③, after the reaction is carried out for 1h, the rotation speed is adjusted downwards from 900r/min, the adjustment range is 300r/min, the reaction is carried out for 2h at the rotation speed after the adjustment downwards, ④ is opened to start overflowing, the overflow pipe is the feeding amount within 2h of the step ③, the solution amount in the continuous stirring liquid phase reactor is recovered to the solution amount at the start time of the step 2, ⑤ is repeated, the step 387, the total feeding time of the first-stage feeding;
in the step five ①, the volume of the complexing agent aqueous solution B is 72 percent of the volume of the continuous stirring liquid phase reactor, wherein the volume of the complexing agent aqueous solution B is 720mL, and the volume of the continuous stirring liquid phase reactor is 1L;
feeding rate ratios of four materials of the primary feeding in the step five ② are that the feeding rate ratio of the mixed metal salt aqueous solution A, the precipitator aqueous solution, the complexing agent aqueous solution A and the fluoride aqueous solution A is 1:1:1: 1;
the feeding rates of the mixed metal brine solution B and the mixed metal brine solution A in the step five ② are the same, and the feeding rates of the primary feeding fluoride aqueous solution B and the fluoride aqueous solution A are the same;
sixthly, cooling: stirring for 3h under the condition that the rotating speed is 700r/min to ensure that the continuous stirring liquid phase reactor is cooled to room temperature to obtain precursor material Ni0.481Co0.193Mn0.289Li0.075(CO3)0.9625F0.075；
Seventhly, preparing the gradient fluorine-doped ternary cathode material: firstly, obtaining a precursor material Ni in the sixth step0.481Co0.193Mn0.289Li0.075(CO3)0.9625F0.075Vacuum drying, pre-sintering at 750 deg.C for 8 hr in oxygen atmosphere, and pre-sintering to obtain precursor Ni0.481Co0.193Mn0.289Li0.075(CO3)0.9625F0.075And lithium carbonate according to a molar ratio of 1:1, uniformly mixing, sintering for 10 hours at the temperature of 850 ℃ in the pure oxygen atmosphere, and sieving to obtain a powdery gradient fluorine-doped ternary cathode material LiNi with low lattice stress0.481Co0.193Mn0.289O1.925F0.075。
The difference between the third test and the first test is as follows: in the second step, the precipitator is a mixture of sodium hydroxide and lithium hydroxide, wherein the molar ratio of the sodium hydroxide to the lithium hydroxide is 1:1.
the fourth test and the first test are different in that: and in the third step, the complexing agent is a mixture of ammonia water and ammonium chloride, wherein the molar ratio of the ammonia water to the ammonium chloride is 1: and M is a mixture of magnesium and aluminum and exists in the forms of magnesium sulfate and aluminum sulfate respectively, wherein the molar ratio of the magnesium sulfate to the aluminum sulfate is 1:1.
the difference between the fifth test and the first test is as follows: the fluoride in the fourth step is a mixture of sodium fluoride and ammonium fluoride, wherein the molar ratio of the sodium fluoride to the ammonium fluoride is 1:1.
the difference between the sixth test and the first test is that the molar ratio of the nickel element to the cobalt element to the manganese element to the Li element in the ① mixed metal salt aqueous solution A in the first step is 7.2: 0.9: 0.9: 1.
Run seven, this run differs from run one in that the total reaction time in step five ⑤ was 16 h.
Run eight, this run differs from run one in that the pH of the reaction in step five ② was set to 10.7. + -. 0.3.
The difference between the ninth test and the first test is as follows: in the third step, the concentration of ammonia water in the complexing agent aqueous solution A is 0.6mol/L, in the first step, M is a mixture of calcium and magnesium, and the ammonia water and the magnesium exist in the forms of calcium nitrate and magnesium sulfate respectively, wherein the molar ratio of the calcium nitrate to the magnesium sulfate is 1:1.
the difference between the tenth test and the first test is as follows: in the first step, the nickel salt is nickel chloride, the cobalt salt is cobalt chloride, and the manganese salt is manganese chloride.
The difference between the first test and the second test is as follows: and seventhly, the molar ratio of the presintered precursor material to the lithium carbonate is 1: 1.2.

Claims (6)

1. A preparation method of a gradient fluorine-doped ternary cathode material with low lattice stress is characterized in that the preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress is carried out according to the following steps:
①, mixing nickel salt, cobalt salt, manganese salt and M salt according to a molar ratio to prepare a mixed metal salt aqueous solution A, wherein the concentration of the mixed metal salt in the mixed metal salt aqueous solution A is 0.01-20 mol/L, and the molar ratio of nickel element, cobalt element, manganese element and M element in the mixed metal salt aqueous solution A is nickel element, cobalt element, manganese element and M element x1:y1:z1:(1-x1-y1-z1) (ii) a Wherein x is more than or equal to 01≤1，0≤y1≤1，0≤z1≤1，0<x1+y1+z1② adding nickel salt, cobalt salt and manganese saltMixing with M salt according to a molar ratio to prepare a mixed metal salt water solution B; the concentration of the mixed metal salt in the mixed metal salt water solution B is 0.01-20 mol/L; the molar ratio of the mixed metal salt aqueous solution B is nickel element: cobalt element: manganese element: m element ═ x2:y2:z2:(1-x2-y2-z2) (ii) a Wherein x is more than or equal to 02≤1，0≤y2≤1，0≤z2≤1，0<x2+y2+z2≤1、x2:y2:z2:(1-x2-y2-z2)≠x1:y1:z1:(1-x1-y1-z1) And x1And x2Is not 0 and y simultaneously1And y2Is not 0 and z simultaneously1And z2Not simultaneously 0;
the M salt is one or a mixture of more of soluble sulfate, soluble nitrate, soluble acetate, soluble chloride, soluble citrate and soluble alkoxide; wherein M is one or a mixture of more of Li, Zr, Fe, Sm, Pr, Nb, Ga, Zn, Y, Mg, Al, Cr, Ca, Na, Ti, Cu, K, Sr, Mo, Ba, Ce, Sn, Sb, La and Bi;
secondly, preparing a precipitant aqueous solution: mixing a precipitator with water to prepare a precipitator aqueous solution with the concentration of 0.01-20 mol/L;
preparing a complexing agent aqueous solution, wherein ① the complexing agent is mixed with water to prepare a complexing agent aqueous solution A, the concentration of the complexing agent in the complexing agent aqueous solution A is 0.01-20 mol/L, ② the complexing agent is mixed with water to prepare a complexing agent aqueous solution B, and the concentration of the complexing agent in the complexing agent aqueous solution B is 0.01-10 mol/L;
fourthly, preparing a fluoride aqueous solution, ① mixing fluoride with water to prepare a fluoride aqueous solution A, wherein the concentration of the fluoride in the fluoride aqueous solution A is 0.001-2 mol/L, ② mixing the fluoride with water to prepare a fluoride aqueous solution B, and the concentration of the fluoride in the fluoride aqueous solution B is 0-2 mol/L;
①, adding a complexing agent aqueous solution B in the third step into a continuous stirring liquid phase reactor to serve as a reaction base solution, ②, then, under the conditions that an inert atmosphere, the pH value is 4-14, the temperature is kept at 10-85 ℃ and the rotating speed is 600-1000 r/min, continuously injecting a mixed metal saline solution A, a precipitator aqueous solution, a complexing agent aqueous solution A and a fluoride aqueous solution A as first-stage feeding materials into the continuous stirring liquid phase reactor respectively, injecting the mixed metal saline solution B and the fluoride aqueous solution B as second-stage feeding materials into the mixed metal saline solution A and the fluoride aqueous solution A respectively while injecting the first-stage feeding materials, continuously injecting the first-stage feeding materials and the second-stage feeding materials into the continuous stirring liquid phase reactor, wherein the adding of the first-stage feeding materials and the second-stage feeding materials lasts for the whole preparation process, when the solid-liquid mass ratio in the continuous stirring liquid phase reactor is 1/40-1/5 during the reaction of ③, the rotating speed is reduced from 600 r/min-1000 r/min, the reduction range is 200 r/300 r/min, the reaction is carried out for 0.5-2 h, ④ is opened to start overflowing, the time of the adding of the overflow pipe is 357, the continuous stirring liquid phase solution, the reaction is carried out, and the step of the step is repeated, the step of the step;
in the step five ①, the volume of the complexing agent aqueous solution B is 10-80% of the volume of the continuous stirring liquid phase reactor;
the feeding rate ratio of the four substances of the primary feeding in the step five ② is that the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(OH)2-nFnFeeding rate ratio of the mixed metal salt aqueous solution A to the precipitant aqueous solution to the complexing agent aqueous solution A to the fluoride aqueous solution A is 1:2:1: 1; the chemical formula of the precursor material is NixCoyMnzM1-x-y-z(CO3)1-0.5nFnFeeding rate ratio of the mixed metal salt aqueous solution A to the precipitant aqueous solution to the complexing agent aqueous solution A to the fluoride aqueous solution A is 1:1:1: 1;
the feeding rates of the mixed metal brine solution B and the mixed metal brine solution A in the step five ② are the same, and the feeding rates of the primary feeding fluoride aqueous solution B and the fluoride aqueous solution A are the same;
in the fifth step ②, the ratio of the total moles of complexing agent in the complexing agent aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-10.0: 1, the ratio of the moles of precipitant in the precipitant aqueous solution to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.1-4.0: 1, and the ratio of the total moles of fluoride in the fluoride aqueous solution A, B to the total moles of metal salts in the mixed metal salt aqueous solution A, B is 0.001-2.0: 1;
sixthly, cooling: stirring for 1-3 h under the condition that the rotating speed is 500-1000 r/min to reduce the temperature of the continuous stirring liquid phase reactor to room temperature to obtain precursor material Ni with low lattice stressxCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1-0.5nFn；
Seventhly, preparing the gradient fluorine-doped ternary cathode material: firstly, obtaining a precursor material Ni in the sixth stepxCoyMnzM1-x-y-z(OH)2-nFnOr NixCoyMnzM1-x-y-z(CO3)1-0.5nFnVacuum drying, pre-sintering for 6-10 h at 700-800 ℃ in an oxygen atmosphere, and then mixing the pre-sintered precursor material with a lithium source according to a molar ratio of 1: (1-1.25), uniformly mixing, sintering for 1-45 h at 500-1000 ℃ in pure oxygen or air atmosphere, and sieving to obtain the ternary oxide positive electrode material LiNi with low lattice stressxCoyMnzM1-x-y-zO2-nFn。
2. The preparation method of the gradient fluorine-doped ternary cathode material with low lattice stress according to claim 1, characterized in that in the step one, the nickel salt is one or a mixture of several of nickel sulfate, nickel nitrate, nickel acetate and nickel chloride; the cobalt salt is one or a mixture of more of cobalt sulfate, cobalt nitrate, cobalt acetate and cobalt chloride; the manganese salt is one or a mixture of manganese sulfate, manganese nitrate, manganese acetate and manganese chloride.
3. The method according to claim 1, wherein the precursor material in step two is NixCoyMnzM1-x-y-z(OH)2-nFnThe precipitant is one or a mixture of several of sodium hydroxide, potassium hydroxide and lithium hydroxide; the precursor material is NixCoyMnzM1-x-y-z(CO3)1-0.5nFnThe precipitator is one or a mixture of more of sodium carbonate, potassium carbonate and lithium carbonate.
4. The method for preparing the gradient fluorine-doped ternary cathode material with low lattice stress as claimed in claim 1, wherein the complexing agent in step three is one or a mixture of more of ammonia, ammonium chloride, ammonium fluoride, ammonium carbonate, ammonium nitrate, ammonium sulfate, ammonium acetate, EDTA, ammonium citrate, ethylenediamine, acetic acid, sodium fluoride, tartaric acid, maleic acid, succinic acid, citric acid and malonic acid.
5. The method for preparing the gradient fluorine-doped ternary cathode material with low lattice stress according to claim 1, wherein the fluoride in the fourth step is one or a mixture of sodium fluoride, potassium fluoride and ammonium chloride.
6. The method for preparing a gradient fluorine-doped ternary cathode material with low lattice stress as claimed in claim 1, wherein the lithium source in step seven is one or a mixture of several of lithium hydroxide, lithium nitrate, lithium sulfate, lithium chloride, lithium fluoride, lithium oxalate, lithium phosphate, lithium hydrogen phosphate and lithium carbonate.
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