CN115084503B - Positive electrode material and preparation method and application thereof - Google Patents

Positive electrode material and preparation method and application thereof Download PDF

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CN115084503B
CN115084503B CN202210656687.9A CN202210656687A CN115084503B CN 115084503 B CN115084503 B CN 115084503B CN 202210656687 A CN202210656687 A CN 202210656687A CN 115084503 B CN115084503 B CN 115084503B
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positive electrode
nickel
precursor
solution
electrode material
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CN115084503A (en
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范亮姣
张坤
华文超
李聪
许开华
杨幸
吕豪
袁文芳
岳先锦
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GEM Co Ltd China
Jingmen GEM New Material Co Ltd
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Jingmen GEM New Material Co Ltd
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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
    • H01M4/52—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
    • 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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • 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
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • 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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/621—Binders
    • H01M4/622—Binders being polymers
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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

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Abstract

The invention provides a positive electrode material, a preparation method and application thereof, wherein the preparation method comprises the following steps: (1) Mixing nickel cobalt binary salt solution, alkali liquor and ammonia water, and adjusting pH to perform one-step coprecipitation reaction to obtain precursor kernel solution; (2) Mixing the precursor core solution obtained in the step (1) with a low crosslinking agent, stirring to obtain a mixed solution, adding a nickel-cobalt-manganese ternary salt solution, alkali liquor and ammonia water, and performing a two-step coprecipitation reaction to obtain a precursor; (3) The precursor obtained in the step (2) is mixed with a lithium source, and the positive electrode material is obtained through sintering treatment, the active material with high specific capacity is used as an inner core, the active material with high stability is used as an outer shell, the combined positive electrode material with the core-shell structure is formed by connecting the inner core with the outer shell through adding a low cross-linking agent, and Li is increased + Migration channels to reduce Ni formation of internal high nickel material 4+ Contact with electrolyte to reduce gas production.

Description

Positive electrode material and preparation method and application thereof
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a positive electrode material, a preparation method and application thereof.
Background
With the popularization of electric vehicles, new energy industries such as electric vehicles have become a growing hotspot. The lithium ion battery is suitable for a power system of an electric automobile, and the positive electrode material of the power battery which is formed by six or seven parts in the market is made of ternary materials. Compared with the lithium cobaltate battery material, the ternary positive electrode material has the advantages of low cost, low toxicity, high specific capacity and the like, and is one of the positive electrode materials of the power battery with the most application prospect. However, the problems of poor rapid charge and discharge performance, unstable structure of the high-nickel ternary material and the like of the low-nickel ternary material severely restrict the large-scale application of the ternary material.
With the increase of the nickel content, the specific capacity of the ternary positive electrode material is gradually increased, but the cycle performance and the safety performance are correspondingly reduced, the surface coating can effectively inhibit the side reaction of the high-nickel material and the electrolyte, the cycle stability of the material is improved, but the shell is too thin, and the improvement of the material performance is not obvious; the shell is too thick, the specific capacity of the material is lost more, and the membrane is dropped after the cycle is repeated for many times.
The ternary positive electrode material with the core-shell structure is generally composed of a core with high specific capacity and a shell with high stability, wherein the core and the shell have electrochemical activity, and have the advantages of high specific capacity, good cycling stability and the like.
CN108448083a discloses a ternary positive electrode material of a lithium battery with a core-shell structure and a preparation method. The preparation method comprises the following preparation processes: (1) 30-35 parts of ternary positive electrode material precursor and 40-50 parts of organic solvent are ground to nano-scale, and then are compounded with 20-25 parts of microporous hollow spherical lithium-rich compound, so that the ternary positive electrode material precursor fully enters the hollow of the microporous hollow spherical lithium-rich compound, and the powder material with a core-shell structure is prepared by heating and pre-firing; (2) Immersing the powder material into lithium salt solution, and rapidly stirring for 2-2.5 h at 70-90 ℃; (3) And (3) filtering, drying, and then performing solid-phase sintering for 3-5 hours at 300-350 ℃ to obtain the ternary positive electrode material of the lithium battery with the core-shell structure.
CN108793268A discloses a core-shell structure gradient nickel-cobalt-manganese ternary positive electrode material precursor and a preparation method thereof, wherein the ternary positive electrode material precursor is core-shell structure particles with average particle diameter of 4-12 μm; wherein the inner core is hydroxide sediment of nickel, cobalt and manganese, the shell layer is carbonate sediment of nickel, cobalt and manganese, the nickel content gradually decreases from the center of the core-shell structure particle to the surface of the shell layer, the manganese content gradually increases from the center of the core-shell structure particle to the surface of the shell layer, and the cobalt content is uniformly distributed in the center of the core-shell structure particle and the shell layer.
According to the positive electrode material, when the composition and the structure of the core material and the shell material are greatly different, gaps are formed between the core and the shell after long-time charge and discharge, and the core gradually loses a lithium ion migration channel, so that the specific capacity of the material is sharply reduced.
Disclosure of Invention
The invention aims to provide a positive electrode material, a preparation method and application thereof, wherein the positive electrode material with a core-shell structure is formed by combining an active material with high specific capacity as a core and a high-stability active material as a shell, and the positive electrode material with a core-shell structure is used for relieving serious particle cracking and shell falling caused by internal strain generated between secondary particles, so that the core and the shell realize functional compounding and complementation, and Li is increased by adding a low cross-linking agent to connect the core and the shell + Migration channels to reduce Ni formation of internal high nickel material 4+ Contact with electrolyte to reduce gas production.
In order to achieve the aim of the invention, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a method for preparing a positive electrode material, the method comprising the steps of:
(1) Mixing nickel cobalt binary salt solution, alkali liquor and ammonia water, and adjusting pH to perform one-step coprecipitation reaction to obtain precursor kernel solution;
(2) Mixing the precursor core solution obtained in the step (1) with a low crosslinking agent, stirring to obtain a mixed solution, adding a nickel-cobalt-manganese ternary salt solution, alkali liquor and ammonia water, and performing a two-step coprecipitation reaction to obtain a precursor;
(3) And (3) mixing the precursor obtained in the step (2) with a lithium source, and performing sintering treatment to obtain the positive electrode material.
According to the invention, the low cross-linking agent is added between the nickel-cobalt binary core and the nickel-cobalt-manganese ternary shell for connection to form a yolk-like shell structure, the specific capacity of the nickel-cobalt binary core is higher, the stability of the nickel-cobalt-manganese ternary shell is better, and Li can be increased by adding the low cross-linking agent + Migration channels to reduce Ni formation of internal high nickel material 4+ The electrolyte contacts with the core, gas production is reduced, and serious particle cracking and shell falling caused by internal strain generated between secondary particles are relieved, so that the core and the shell realize functional compounding and complementation, and the problems of specific capacity improvement, structural stability improvement, cyclical stability improvement and the like are solved.
Preferably, the molar ratio of nickel ions to cobalt ions in the nickel cobalt binary salt solution in the step (1) is (70-100): (1-30), for example: 70:30, 75:25, 80:20, 85:15, or 90:10, etc.
Preferably, the total molar concentration of metal ions in the nickel cobalt binary salt solution is 1.5-3 mol/L, for example: 1.5mol/L, 1.8mol/L, 2mol/L, 2.5mol/L, 3mol/L, etc.
Preferably, the lye comprises sodium hydroxide solution.
Preferably, the pH of step (1) is adjusted to 10 to 12, for example: 10. 10.5, 11, 11.5 or 12, etc.
Preferably, the one-step coprecipitation reaction is carried out for 50 to 100 hours, for example: 50h, 60h, 70h, 80h, 90h or 100h, etc.
Preferably, the supernatant of the precursor core solution is withdrawn before the mixing in step (2).
Preferably, the low crosslinking agent of step (2) comprises any one or a combination of at least two of maleic anhydride, succinic acid, glutaraldehyde, N-methylenebisacrylamide, or methacrylic acid.
Preferably, the stirring time is 10 to 30min, for example: 10min, 15min, 20min, 25min or 30min, etc.
Preferably, the volume ratio of the precursor core solution to the low crosslinking agent is (20-70): (5-20), for example: 20:5, 30:6, 20:8, 40:15, or 70:20, etc.
Preferably, the molar ratio of nickel ions, cobalt ions and manganese ions in the nickel-cobalt-manganese ternary salt solution in the step (2) is (20-80): (1-20): (20-70), for example: 20:2:40, 40:10:60, 60:10:30, 20:10:70 or 40:5:55, etc.
Preferably, the total molar concentration of metal ions in the nickel cobalt manganese ternary salt solution is 1.5-3 mol/L, for example: 1.5mol/L, 1.8mol/L, 2mol/L, 2.5mol/L, 3mol/L, etc.
Preferably, the lye comprises sodium hydroxide solution.
Preferably, the two-step coprecipitation reaction takes 20 to 50 hours, for example: 20h, 25h, 30h, 40h or 50h, etc.
Preferably, the lithium source of step (3) comprises lithium hydroxide and/or lithium carbonate.
Preferably, the molar ratio of the precursor to the lithium element in the lithium source is 1 (1.01-1.2), for example: 1:1.01, 1:1.05, 1:1.08, 1:1.1, 1:1.15, or 1:1.2, etc.
Preferably, the sintering treatment is carried out at a temperature of 600 to 800 ℃, for example: 600 ℃, 650 ℃, 700 ℃, 750 ℃, 800 ℃, etc.
Preferably, the sintering treatment is carried out for a period of time ranging from 5 to 15 hours, for example: 5h, 8h, 10h, 12h or 15h, etc.
In a second aspect, the present invention provides a positive electrode material made by the method of the first aspect, the positive electrode material comprising a binary inner core, a ternary outer shell, and a low crosslinker layer disposed between the binary inner core and the ternary outer shell;
the molecular formula of the binary kernel is Ni m Co 1-m (OH) 2 Wherein m is more than 0.7 and less than 1;
the molecular formula of the ternary shell is Ni x Co y Mn 1-x-y (OH) 2 Wherein x is more than or equal to 0.5 and less than or equal to 0.9,0.05, and y is more than or equal to 0.2..
The invention designs the anode material into the high-manganese composite structure of the inner core high-nickel material shell, and adds the low cross-linking agent for connection, thereby increasing Li + Migration channels to reduce Ni formation of internal high nickel material 4+ The electrolyte contacts with the core, gas production is reduced, and serious particle cracking and shell falling caused by internal strain generated between secondary particles are relieved, so that the core and the shell realize functional compounding and complementation, and the problems of specific capacity improvement, structural stability improvement, cyclical stability improvement and the like are solved.
In a third aspect, the present invention provides a positive electrode sheet comprising the positive electrode material according to the second aspect.
In a fourth aspect, the present invention provides a lithium ion battery comprising the positive electrode sheet according to the third aspect.
Compared with the prior art, the invention has the following beneficial effects:
(1) The invention uses the active material with high specific capacity as the inner core, the high stable active material as the outer shell, the combined core-shell structure positive electrode material relieves the serious particle cracking and shell layer falling caused by internal strain generated between the secondary particles, thereby realizing the functional compounding and complementation of the core and the shell, improving the specific capacity, improving the structural stability and the cyclical stability, and the like, and the low cross-linking agent is added to connect the inner core and the outer shell, thereby increasing Li + Migration channels to reduce Ni formation of internal high nickel material 4+ Contact with electrolyte to reduce gas production.
(2) The battery prepared by the positive electrode material can have a specific capacity of 210.1mAh/g after first discharge at 0.1C rate, and the capacity retention rate of the battery after 100 charge and discharge cycles at 50 ℃ is as high as 94.9%.
Drawings
Fig. 1 is a schematic structural diagram of the positive electrode material described in example 1, wherein 1 is a shell, 2 is a low-crosslinking agent layer, and 3 is a core.
Fig. 2 is a schematic structural diagram of the positive electrode material of comparative example 1, 4 is a shell, and 5 is a core.
Detailed Description
The technical scheme of the invention is further described by the following specific embodiments. It will be apparent to those skilled in the art that the examples are merely to aid in understanding the invention and are not to be construed as a specific limitation thereof.
Example 1
The embodiment provides a positive electrode material, and the preparation method of the positive electrode material comprises the following steps:
(1) Preparing binary salt solution A of nickel ions and cobalt ions according to the molar ratio of 95:5, a step of; the molar ratio of the nickel ions, the cobalt ions and the manganese ions of the ternary salt solution B is 75:5:20, wherein the total concentration of nickel ions, cobalt ions and manganese ions in the salt solution is 2mol/L;
(2) Adding the binary salt solution A in the step (1) into a reaction kettle at the speed of 5L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in the reaction kettle to 11.3-11.7 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 50 hours to obtain a core part of the precursor;
(3) After the step (2) is finished, suspending feeding of the binary salt solution, the liquid alkali and the ammonia water, stopping stirring for 10min, extracting the clear liquid, starting stirring, pumping 100L of low-crosslinking agent methacrylic acid, and stirring for 30min;
(4) After the step (3) is finished, adding the ternary salt solution B in the step (1) into a reaction kettle at a certain rate of 4L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in a reaction kettle to be 10.5-10.9 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 20 hours to obtain a precursor;
(5) Sequentially performing centrifugal washing, drying and screening to remove iron on the solid-liquid mixture obtained in the step (4) to obtain a precursor of the high-nickel anode material with the yolk shell structure; the drying temperature is 110 ℃;
(6) Uniformly mixing the positive electrode material precursor obtained in the step (5) with lithium hydroxide according to a molar ratio of 1:1.01, roasting in a muffle furnace, and cooling, crushing and sieving to obtain the positive electrode material; the whole roasting process maintains oxygen atmosphere, and the roasting process conditions are as follows: and heat treatment is carried out at 750 ℃ for 15h.
The structural schematic diagram of the positive electrode material is shown in fig. 1, wherein 1 is a shell, 2 is a low cross-linking agent layer, and 3 is a core.
Example 2
The embodiment provides a positive electrode material, and the preparation method of the positive electrode material comprises the following steps:
(1) The molar ratio of the nickel ions to the cobalt ions of the binary salt solution A is 80:20, a step of; the molar ratio of the nickel ions, the cobalt ions and the manganese ions of the ternary salt solution B is 60:10:30, wherein the total concentration of nickel ions, cobalt ions and manganese ions in the salt solution is 2mol/L;
(2) Adding the binary salt solution A in the step (1) into a reaction kettle at a certain speed of 4L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in the reaction kettle to 11.1-11.5 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 70 hours to obtain a core part of the precursor;
(3) After the step (2) is finished, suspending feeding of the binary salt solution, the liquid alkali and the ammonia water, stopping stirring for 5min, extracting the clear liquid, starting stirring, pumping 50L of low-crosslinking agent maleic anhydride, and stirring for 20min;
(4) After the step (3) is finished, adding the ternary salt solution B in the step (1) into a reaction kettle at a certain rate of 7L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in a reaction kettle to be 10.3-10.7 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 40 hours to obtain a precursor;
(5) Sequentially performing centrifugal washing, drying and screening to remove iron on the solid-liquid mixture obtained in the step (4) to obtain a precursor of the high-nickel anode material with the yolk shell structure; the drying temperature is 150 ℃;
(6) Uniformly mixing the positive electrode material precursor obtained in the step (5) with lithium hydroxide according to a molar ratio of 1:1.2, roasting in a muffle furnace, and cooling, crushing and sieving to obtain the positive electrode material; the whole roasting process maintains oxygen atmosphere, and the roasting process conditions are as follows: heat treatment is carried out at 800 ℃ for 5 hours.
Example 3
The embodiment provides a positive electrode material, and the preparation method of the positive electrode material comprises the following steps:
(1) Preparing binary salt solution A, wherein the molar ratio of nickel ions to cobalt ions is 72:28; the mole ratio of the nickel ions, the cobalt ions and the manganese ions of the ternary salt solution B is 25:5:70, wherein the total concentration of nickel ions, cobalt ions and manganese ions in the salt solution is 2mol/L;
(2) Adding the binary salt solution A in the step (1) into a reaction kettle at a certain speed of 7L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in the reaction kettle to 11.0-11.4 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 100 hours to obtain a core part of the precursor;
(3) After the step (2) is finished, suspending feeding of the binary salt solution, the liquid alkali and the ammonia water, stopping stirring for 20min, extracting the clear liquid, starting stirring, pumping 200L of low-crosslinking agent glutaraldehyde, and stirring for 10min;
(4) After the step (3) is finished, adding the ternary salt solution B in the step (1) into a reaction kettle at a certain speed of 12L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in a reaction kettle to be 10.0-10.5 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 50 hours to obtain a precursor;
(5) Sequentially performing centrifugal washing, drying and screening to remove iron on the solid-liquid mixture obtained in the step (4) to obtain a precursor of the high-nickel anode material with the yolk shell structure; the drying temperature is 80 ℃;
(6) Uniformly mixing the positive electrode material precursor obtained in the step (5) with lithium hydroxide according to a molar ratio of 1:1.05, roasting in a muffle furnace, and cooling, crushing and sieving to obtain a positive electrode material of the lithium ion battery; the whole roasting process maintains oxygen atmosphere, and the roasting process conditions are as follows: heat treatment at 600 deg.c for 12 hr.
Example 4
This example differs from example 1 only in that the volume of low crosslinker added is 30L, the other conditions and parameters being exactly the same as in example 1.
Example 5
This example differs from example 1 only in that the volume of low crosslinker added is 250L, the other conditions and parameters being exactly the same as example 1.
Comparative example 1
(1) Respectively preparing salt solutions of nickel, cobalt and manganese, wherein the salt solution is one of sulfate solution, nitrate solution or chloride salt solution; the molar ratio of the nickel ions to the cobalt ions in the binary salt solution A in the salt solution is 95:5, a step of; the molar ratio of the nickel ions, the cobalt ions and the manganese ions of the ternary salt solution B is 75:5:20, wherein the total concentration of nickel ions, cobalt ions and manganese ions in the salt solution is 2mol/L;
(2) Adding the binary salt solution A in the step (1) into a reaction kettle at the speed of 5L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in the reaction kettle to 11.3-11.7 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 50 hours to obtain a core part of the precursor;
(4) After the step (3) is finished, adding the ternary salt solution B in the step (1) into a reaction kettle at a certain rate of 4L/h; at N 2 In the atmosphere, regulating the pH value of a solid-liquid mixture in a reaction kettle to be 10.8-11.1 through a sodium hydroxide solution and an ammonia water solution with a certain concentration, and performing coprecipitation reaction for 20 hours to obtain a precursor;
(5) Sequentially performing centrifugal washing, drying and screening to remove iron on the solid-liquid mixture obtained in the step (4) to obtain a core-shell structure high-nickel cathode material precursor; the drying temperature is 120 ℃;
(6) Uniformly mixing the positive electrode material precursor obtained in the step (5) with lithium hydroxide according to a molar ratio of 1:1.05, roasting in a muffle furnace, and cooling, crushing and sieving to obtain the positive electrode material; the whole roasting process maintains oxygen atmosphere, and the roasting process conditions are as follows: heat treatment is carried out at 800 ℃ for 10 hours.
The structural schematic diagram of the positive electrode material is shown in fig. 2, wherein 4 is a shell, and 5 is a core.
Comparative example 2
This comparative example differs from example 1 only in that a ternary salt solution was added first, followed by a binary salt solution, and other conditions and parameters were exactly the same as example 1.
Performance test:
the positive electrode materials obtained in examples 1-5 and comparative examples 1-2 were made into positive electrode sheets, and 7 button cells were assembled with metallic lithium sheets as negative electrodes, respectively, for charge-discharge comparison tests, and the test results are shown in table 1:
TABLE 1
As can be seen from Table 1, the battery prepared from the positive electrode material can achieve a specific capacity of over 198.5mAh/g at a rate of 0.1C, a capacity retention rate after 100 charge-discharge cycles at 25 ℃ can achieve over 97.4%, a capacity retention rate after 100 charge-discharge cycles at 50 ℃ can achieve over 84.6%, the battery prepared from the positive electrode material can achieve a specific capacity of 210.1mAh/g at a rate of 0.1C, a capacity retention rate after 100 charge-discharge cycles at 25 ℃ can achieve 98.1%, a capacity retention rate after 100 charge-discharge cycles at 50 ℃ can achieve 94.9%, and a capacity retention rate after 100 charge-discharge cycles at 50 ℃ can achieve 75.4% by adjusting conditions in the preparation process.
As can be seen from the comparison of examples 1 and 4-5, in the preparation process of the positive electrode material of the present invention, the volume ratio of the precursor core solution to the low crosslinking agent affects the performance of the positive electrode material, the volume ratio of the precursor core solution to the low crosslinking agent is controlled to be (20-70): 5-20, the performance of the positive electrode material is good, if the addition amount of the low crosslinking agent is too large, the lithium ion channel is too long, the circulation efficiency is affected, if the addition amount of the low crosslinking agent is too small, the Ni generated by the internal high nickel material 4+ Contact with the electrolyte is still possible to produce gas, and the cracking of particles or the falling of a shell layer are seriously possible.
The positive electrode material for the lithium ion battery with the yolk shell structure material obtained by the invention has higher specific discharge capacity than that of a battery obtained by the positive electrode material for the high-nickel battery with the common core-shell structure with the same composition, and the capacity retention rate after charge and discharge cycles of the positive electrode material for the lithium ion battery with the yolk shell structure material is higher than that of the positive electrode material for the high-nickel battery with the common core-shell structure.
The invention uses high specific capacity active material as inner core and high stable active material as outer shell, to form the core-shell structure positive electrode material, to release the serious particle crack and shell layer drop caused by internal strain between secondary particles, to realize functional compound and complement between core and shell, to improve specific capacity, structure stability and circulation stability.
The applicant declares that the above is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be apparent to those skilled in the art that any changes or substitutions that are easily conceivable within the technical scope of the present invention disclosed by the present invention fall within the scope of the present invention and the disclosure.

Claims (19)

1. A method for preparing a positive electrode material, comprising the steps of:
(1) Mixing nickel cobalt binary salt solution, alkali liquor and ammonia water, and regulating pH value to make first-step coprecipitation reaction so as to obtain precursor kernel solution;
(2) Mixing the precursor core solution obtained in the step (1) with a low crosslinking agent, stirring to obtain a mixed solution, adding a nickel-cobalt-manganese ternary salt solution, alkali liquor and ammonia water, and performing a second-step coprecipitation reaction to obtain a precursor;
(3) Mixing the precursor obtained in the step (2) with a lithium source, and performing sintering treatment to obtain the anode material;
the low cross-linking agent in the step (2) comprises any one or a combination of at least two of maleic anhydride, succinic acid, glutaraldehyde, N-methylene bisacrylamide or methacrylic acid, and the volume ratio of the precursor core solution to the low cross-linking agent is (20-70) (5-20).
2. The method of claim 1, wherein the molar ratio of nickel ions to cobalt ions in the nickel cobalt binary salt solution in step (1) is (70-100): 1-30.
3. The method according to claim 1, wherein the total molar concentration of metal ions in the nickel cobalt binary salt solution in the step (1) is 1.5 to 3mol/L.
4. The process according to claim 1, wherein the lye of step (1) comprises sodium hydroxide solution.
5. The method according to claim 1, wherein the pH is adjusted to 10 to 12 in the step (1).
6. The method according to claim 1, wherein the first coprecipitation reaction time is 50 to 100 hours.
7. The method of claim 1, wherein the supernatant of the precursor core solution is withdrawn prior to the mixing in step (2).
8. The method according to claim 1, wherein the stirring time is 10 to 30 minutes.
9. The preparation method according to claim 1, wherein the molar ratio of nickel ions, cobalt ions and manganese ions in the nickel-cobalt-manganese ternary salt solution in the step (2) is (20-80): (1-20): (20-70).
10. The method of claim 1, wherein the total molar concentration of metal ions in the nickel cobalt manganese ternary salt solution is 1.5 to 3mol/L.
11. The process according to claim 1, wherein the lye of step (2) comprises sodium hydroxide solution.
12. The method according to claim 1, wherein the second coprecipitation reaction time is 20 to 50 hours.
13. The method of claim 1, wherein the lithium source of step (3) comprises lithium hydroxide and/or lithium carbonate.
14. The method of claim 1, wherein the molar ratio of the precursor in step (3) to the lithium element in the lithium source is 1 (1.01-1.2).
15. The method of claim 1, wherein the sintering treatment in step (3) is performed at a temperature of 600 to 800 ℃.
16. The method according to claim 1, wherein the sintering treatment in step (3) is performed for a period of 5 to 15 hours.
17. A positive electrode material, characterized in that it is produced by the method according to any one of claims 1-16, comprising a binary inner core, a ternary outer shell and a low cross-linker layer arranged between the binary inner core and the ternary outer shell;
the molecular formula of the binary kernel is Ni m Co 1-m (OH) 2 Wherein m is more than 0.7 and less than 1;
the molecular formula of the ternary shell is Ni x Co y Mn 1-x-y (OH) 2 Wherein x is more than or equal to 0.5 and less than or equal to 0.9,0.05, and y is more than or equal to 0.2.
18. A positive electrode sheet comprising the positive electrode material of claim 17.
19. A lithium ion battery comprising the positive electrode sheet of claim 18.
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