CN111900361A - Positive active material, preparation method thereof and application thereof in lithium ion secondary battery - Google Patents

Positive active material, preparation method thereof and application thereof in lithium ion secondary battery Download PDF

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CN111900361A
CN111900361A CN202010851775.5A CN202010851775A CN111900361A CN 111900361 A CN111900361 A CN 111900361A CN 202010851775 A CN202010851775 A CN 202010851775A CN 111900361 A CN111900361 A CN 111900361A
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active material
positive electrode
core
equal
electrode active
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樊亚楠
曾家江
李素丽
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Zhuhai Cosmx Battery Co Ltd
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Zhuhai Cosmx Battery 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
    • H01M4/362—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
    • 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
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • 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
    • H01M4/36—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
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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 active material, a preparation method thereof and application in a lithium ion secondary battery, wherein the cycle performance of the battery can be effectively improved by introducing the high-voltage lithium cobalt oxide positive active material into the lithium ion secondary battery, and simultaneously, the DSC exothermic peak-emitting temperature of the high-voltage lithium cobalt oxide positive active material shifts to a lower temperature along with the cycle of the lithium ion secondary battery, but the shifting degree is smaller.

Description

Positive active material, preparation method thereof and application thereof in lithium ion secondary battery
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a high-voltage lithium cobaltate positive electrode active material, a preparation method thereof and application thereof in a lithium ion secondary battery.
Background
Since commercialization, lithium ion batteries have been widely used in the digital fields such as notebooks and mobile phones because of their high specific energy and good cycle performance. However, with the increasing demand of human beings for electronic devices, higher requirements are also put forward on the energy density of lithium ion secondary batteries, and the energy density of the batteries has a great relationship with the volume, the discharge voltage platform and the discharge capacity of the batteries, and also has a great relationship with the compaction of materials, so that the improvement of the discharge voltage platform of the batteries becomes one of effective means for improving the energy density of the batteries. However, when the lithium ion battery is charged to 4.2V or more, the positive electrode active material LiCoO2Form Li after lithium ion extraction1-xCoO2(x is more than or equal to 0 and less than or equal to 0.5), continuing charging, and when the charging voltage is increased to be more than 4.4V, LiCoO2More lithium ions are extracted, so that the hexagonal system is transformed into the monoclinic system, and the transformed monoclinic LiCoO2The lithium cobaltate active material no longer has reversible lithium ion de-intercalation capability, and meanwhile, when the battery system reaches 4.4V or more, the side reaction of the positive active material and the electrolyte is gradually intensified, so that the reversible capacity of the lithium cobaltate active material in commercial application at present is far less than the theoretical capacity (274 mAh/g).
Disclosure of Invention
Research shows that in order to improve the overall energy density of the battery from the perspective of the positive electrode active material, the structural stability and the cycling stability of the battery under higher voltage need to be improved, and for the positive electrode active material, certain coating doping modification can be carried out to effectively improve the structural stability and the cycling stability of the positive electrode active material under a high voltage system. The invention relates to a high-voltage lithium cobaltate positive active material, a preparation method thereof and application thereof in a lithium ion secondary battery. Meanwhile, the DSC of the conventional positive active material and the positive active material before and after circulation are compared, and the test result shows that after the circulation of 2.5V-4.45V (for a graphite electrode, 4.45V is not included), the exothermic peak position of the DSC of the conventional positive active material before and after the circulation is obviously moved forward, so that the structural stability of the conventional positive active material is obviously reduced along with the circulation, and the peak position moving amplitude of the exothermic peak of the DSC of the positive active material before and after the circulation is smaller than that of the conventional positive active material, so that the circulation stability and the structural stability of the positive active material are improved by the modification means of the invention.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a positive active material comprises at least one core material and at least one shell material, wherein the at least one shell material is coated on the surface of the at least one core material to form at least one particle with a core-shell structure;
the composition of the at least one core material is the same or different and is selected from Li independently of one anotherxMe1-yMyO2Wherein Me is Co1-a-bAlaZbM is one or more of Al, Mg, Ti, Zr, Co, Ni, Mn, Y, La, Sr, W and Sc, and Z is one or more of Mg, Ti, Zr, Co, Ni and Mn; x is more than or equal to 0.95 and less than or equal to 1.05, y is more than or equal to 0 and less than or equal to 0.1, a is more than or equal to 0 and less than or equal to 0.2, and b is more than or equal to 0 and less than or equal to 0.1;
the composition of the at least one shell material is the same or different and is independently selected from one or more of metal fluorides, metal oxides, metal borate compounds, and metal phosphate compounds.
Specifically, the positive electrode active material comprises at least one core material and at least one shell material, wherein the at least one shell material is coated on the surface of the at least one core material to form at least one particle with a core-shell structure; that is, the formed positive electrode active material may be defined as An × Bn, where An represents at least one core material and Bn represents at least one shell material.
Specifically, the positive active substance comprises two core materials and a shell material, and the shell material is coated on the surfaces of the two core materials to form a particle with a core-shell structure; that is, the formed positive active material may be defined as (a1+ a2) × B1, where a1 and a2 represent two core materials having different compositions, and B1 represents a shell material.
Specifically, the positive active substance comprises two core materials and two shell materials, wherein one shell material is coated on the surface of one core material to form a particle with a core-shell structure, and the other shell material is coated on the surface of the other core material to form another particle with a core-shell structure; that is, the formed positive active material may be defined as a1 × B1+ a2 × B2, where a1 and a2 represent two core materials having different compositions, B1 and B2 represent two shell materials having different compositions, and a1 × B1+ a2 × B2 is the formed two particles having a core-shell structure.
Specifically, when the positive electrode active material includes at least one core material, at least one of the structure, composition, particle size, and addition amount of the plurality of core materials is different, for example, the particle size is different, the composition is different, the structure is different, and the addition amount is different.
Specifically, when the positive electrode active material includes at least one kind of shell material, at least one of the structure, composition, particle size, and addition amount of the plurality of shell materials is different, for example, the particle size is different, the composition is different, the structure is different, and the addition amount is different.
Specifically, the particle diameter D of the positive electrode active material50Is 9.0 to 14.0 μm, such as 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm.
The positive electrode active material may be composed of active materials having the same particle size, or may be obtained by grading a large-particle active material and a small-particle active material, wherein the particle size D of the large-particle active material50A particle diameter D of the active material of 8.0 to 18.0 μm in small particles502.0 to 6.0 μm.
Specifically, the thickness of the shell material in the positive electrode active material is less than or equal to 40nm, such as 5-30nm, such as 5nm, 6nm, 8nm, 10nm, 12nm, 15nm, 18nm, 20nm, 22nm, 23nm, 5nm, 28nm, 30nm, 35nm, 38nm, and 40 nm.
Specifically, the mass of the shell material in the positive electrode active material accounts for 0.03-0.5% of the total mass of the positive electrode active material, such as 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%.
Specifically, the DSC exothermic peak position of the positive electrode sheet before and after the cycle of the lithium ion secondary battery assembled with the positive electrode active material was tested. Compared with the positive plate of the lithium ion secondary battery assembled by the conventional positive active material and the DSC of the positive active material before and after circulation of the positive plate of the invention, the test result shows that after the circulation of 2.5V-4.45V (for a graphite electrode, 4.45V is not included), the exothermic peak position of the DSC before and after the circulation of the conventional positive active material is obviously moved forward, which shows that the structural stability of the conventional positive active material is obviously reduced along with the circulation, while the peak position moving amplitude of the DSC exothermic peak after the circulation of the positive active material of the invention is smaller than that of the conventional positive active material, which shows that the circulation stability of the positive active material is improved by the modification means of the invention.
In particular, the metal fluoride is selected from AlF3、Li3F. One or more of MgF.
Specifically, the metal oxide is selected from Al2O3、TiO2、ZrO2、MgO2One or more of (a).
In particular, the metal borate compound is selected from AlBO3。
In particular, the metal phosphate compound is selected from AlPO4、Li3PO4And the like.
The invention also provides a preparation method of the positive active material, which comprises the following steps:
a) preparing at least one core material;
b) preparing at least one shell material;
c) coating at least one shell material of the step b) on the surface of at least one core material of the step a) to form at least one particle with a core-shell structure.
According to the invention, the core material in step a) is prepared by the following method:
1) preparing a cobalt source, a compound containing an Al element and a compound containing a Z element into an aqueous solution;
2) mixing the aqueous solution, the complex and a precipitator, and reacting to obtain the carbonate MeCO containing Al and Z-doped cobalt3；
3) Carbonate MeCO containing Al and Z-doped cobalt3Calcining to obtain a precursor Me containing Al and Z-doped cobalt3O4；
4) A lithium source, a compound optionally containing an M element, a precursor Me containing Al and Z-doped cobalt3O4And calcining to obtain the core material.
In the step 1), the step (A) is carried out,
specifically, the cobalt source is at least one selected from cobalt acetate, cobalt oxalate, cobalt nitrate, cobalt sulfate, cobalt chloride and cobalt hydroxide.
Specifically, the compound containing the Al element is at least one selected from an oxide, a chloride, a hydroxide, a carbonate, a sulfate, a nitrate, an oxalate and an acetate containing the Al element.
Specifically, the compound containing the Z element is at least one selected from oxides, chlorides, hydroxides, carbonates, sulfates, nitrates, oxalates and acetates containing the Z element.
Specifically, the molar ratio of the cobalt source, the compound containing the Al element and the compound containing the Z element is such that the molar ratio of Co, Al and Z is 1-a-b: a: b, wherein a is more than or equal to 0 and less than or equal to 0.2, and b is more than or equal to 0 and less than or equal to 0.1.
Specifically, the concentration of the cobalt source in the aqueous solution is 0.8-3.8 mol/L.
In the step 2), the step (c) is carried out,
specifically, the complexing agent is selected from ammonia water, and the concentration of the ammonia water is 20-25%.
In particular, the precipitating agent is selected from soluble bases, theThe soluble alkali is selected from Na2CO3、NH4HCO3、(NH4)2CO3And the like.
Specifically, the mass ratio of the complex to the precipitant is 2: 1-1: 1.
Specifically, in the mixed system, the concentration of the precipitant is 0.8-3.8 mol/L.
Specifically, the reaction temperature is 30-80 ℃, and the reaction time is 10-20 hours.
Specifically, the aqueous solution, the complex solution and the precipitant solution may undergo a complex precipitation reaction after being mixed.
In the step 3), the step (c),
specifically, the calcination temperature is 920-1000 ℃, and the calcination time is 8-12 hours. The calcination is carried out under an air atmosphere.
In the step 4), the step of mixing the raw materials,
specifically, the compound containing the M element is at least one selected from oxide, chloride, hydroxide, carbonate, sulfate, nitrate, oxalate and acetate of M.
Specifically, the lithium source is at least one selected from the group consisting of lithium hydroxide, lithium nitrate, lithium carbonate, lithium oxalate, lithium acetate, lithium oxide, and lithium citrate.
In particular, the lithium source, the compound containing M element, the precursor Me containing Al and Z-doped cobalt3O4In such a way that the molar ratio of Li, Me and M is x: 1-y: y, wherein x is more than or equal to 0.95 and less than or equal to 1.05, and y is more than or equal to 0 and less than or equal to 0.1.
Specifically, the calcination temperature is 900-1050 ℃, and the calcination time is 8-12 hours. The calcination is carried out under an air atmosphere.
According to the invention, the core material in step a) is prepared by the following method:
1') preparing a cobalt source into an aqueous solution;
2') mixing the aqueous solution, the complex and a precipitator, and reacting to obtain cobalt carbonate CoCO3；
3’)By the carbonate CoCO of cobalt3Calcining to obtain a precursor Co of cobalt3O4；
4') a lithium source, a compound containing an Al element, a compound containing an Z element, optionally a compound containing an M element, a precursor of cobalt Co3O4And calcining to obtain the core material.
According to the invention, in step b), the shell material is selected from the group consisting of metal oxides, metal fluorides, metal borate compounds, metal phosphate compounds.
According to the invention, said step c) comprises the following steps:
physically mixing at least one core material and at least one shell material, and calcining to obtain at least one particle with a core-shell structure, wherein the surface of at least one core material is coated with at least one shell material.
Specifically, the physical mixing time is 2-4 h; the physical mixing is at least one of stirring, ball milling and grinding, for example; the calcination temperature is 800-1000 ℃, the calcination time is 6-9h, and the calcination is carried out in an air atmosphere.
The invention also provides a positive plate which comprises the positive active material.
According to the present invention, the positive electrode sheet includes a conductive agent and a binder.
Specifically, the positive plate comprises the following components in percentage by mass:
70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent and 0.5-15 wt% of binder.
Specifically, the positive plate comprises the following components in percentage by mass:
80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent and 1-10 wt% of binder.
Specifically, the conductive agent is at least one selected from conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, and carbon fiber.
Specifically, the binder is at least one selected from polyvinylidene fluoride (PVDF), Polytetrafluoroethylene (PTFE), and lithium Polyacrylate (PAALi).
The invention also provides a lithium ion battery which comprises the positive plate.
According to the invention, the lithium ion battery further comprises a negative plate, a diaphragm and electrolyte.
Specifically, the electrolyte comprises a non-aqueous solvent, a conductive lithium salt and an additive, wherein the additive comprises a nitrile compound, vinylene carbonate and 1, 3-propylene sulfonic acid lactone.
Specifically, the non-aqueous organic solvent is selected from a mixture in which at least one of cyclic carbonates and at least one of linear carbonates and linear carboxylates are mixed in an arbitrary ratio.
Specifically, the cyclic carbonate is selected from at least one of ethylene carbonate and propylene carbonate, the linear carbonate is selected from at least one of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate, and the linear carboxylate is selected from at least one of ethyl propionate, propyl propionate and propyl acetate.
Specifically, the nonaqueous organic solvent is calculated by taking the total volume as 100 vol%, wherein the volume fraction of the cyclic carbonate is 20-40 vol%, and the volume fraction of the linear carbonate and/or the linear carboxylic ester is 60-80 vol%.
Specifically, the conductive lithium salt is at least one selected from lithium hexafluorophosphate, lithium bis (fluorosulfonyl) imide and lithium bis (trifluoromethanesulfonyl) imide.
Specifically, the nitrile compound is at least one selected from adiponitrile, succinonitrile and 1, 2-bis (cyanoethoxy) ethane.
Specifically, the negative electrode sheet includes a negative electrode active material, a conductive agent, and a binder.
Specifically, the negative plate comprises the following components in percentage by mass:
70-99 wt% of negative electrode active material, 0.5-15 wt% of conductive agent and 0.5-15 wt% of binder.
Specifically, the negative plate comprises the following components in percentage by mass:
80-98 wt% of negative electrode active material, 1-10 wt% of conductive agent and 1-10 wt% of binder.
Specifically, the negative active material is selected from one or a combination of several of artificial graphite, natural graphite, hard carbon, mesocarbon microbeads, lithium titanate, silicon carbon and silicon monoxide.
Specifically, the used diaphragm is a material taking polypropylene as a base material, or a gummed diaphragm coated with ceramic on one side or two sides on the basis of the material.
According to the invention, the lithium ion battery has a thickness expansion rate of less than or equal to 7 percent, such as less than or equal to 5 percent, after being stored for 35 days at 60 ℃.
According to the invention, the residual capacity of the lithium ion battery after 48 hours of storage at 70 ℃ is more than or equal to 83 percent, such as more than or equal to 85 percent.
According to the invention, the capacity retention rate of the lithium ion battery is more than or equal to 85 percent, such as more than or equal to 90 percent, after the lithium ion battery is cycled for 500 times under the charge-discharge multiplying power of 1C/1C at 45 ℃.
According to the invention, the DSC exothermic peak initial temperature of the positive pole piece before circulation is more than or equal to 270 ℃, such as more than or equal to 280 ℃, such as more than or equal to 290 ℃, and the DSC exothermic peak initial temperature of the positive pole piece after circulation for 500 circles under the charge-discharge multiplying power of 45 ℃ and 1C/1C is more than or equal to 265 ℃, such as more than or equal to 275 ℃, such as more than or equal to 285 ℃.
According to the invention, the DSC exothermic peak initial temperature difference of the positive pole piece before and after 500 cycles at 45 ℃ and 1C/1C charge-discharge multiplying power is less than or equal to 15 ℃, such as less than or equal to 10 ℃.
Has the advantages that:
the invention provides a positive active material, a preparation method thereof and application in a lithium ion secondary battery, wherein the cycle performance of the battery can be effectively improved by introducing the high-voltage lithium cobalt oxide positive active material into the lithium ion secondary battery, and simultaneously, the DSC exothermic peak-emitting temperature of the high-voltage lithium cobalt oxide positive active material shifts to a lower temperature along with the cycle of the lithium ion secondary battery, but the shifting degree is smaller.
Drawings
FIG. 1 is a graph of cycle profiles for example 1, example 3 and comparative example 1;
FIG. 2 is a graph of cycle curves for example 2 and comparative example 1;
FIG. 3 is a graph of cycle profiles for example 2, example 4 and comparative example 1;
FIG. 4 is a graph of cycle profiles for example 5, example 6, example 7 and comparative example 1;
FIG. 5 is a graph of cycle profiles for example 5, example 8 and comparative example 1;
FIG. 6 is a graph of cycle curves for examples 5, 9 and 10;
FIG. 7 is a graph of cycle profiles for example 5, example 11, example 12 and comparative example 1;
FIG. 8 is a DSC curve (4.35V) before and after cycling for comparative example 1 and example 2;
FIG. 9 is a DSC curve (4.4V) before and after cycling for comparative example 1 and example 5.
Detailed Description
The present invention will be described in further detail with reference to specific examples. It is to be understood that the following examples are only illustrative and explanatory of the present invention and should not be construed as limiting the scope of the present invention. All the technologies realized based on the above-mentioned contents of the present invention are covered in the protection scope of the present invention.
The experimental methods used in the following examples are all conventional methods unless otherwise specified; reagents, materials and the like used in the following examples are commercially available unless otherwise specified.
Example 1
The positive active substance with excellent cycle performance in a high-voltage system comprises core materials A1 and A2 and a shell material B1, wherein the shell material B1 is coated on the surfaces of the core materials A1 and A2 to form particles with a core-shell structure; the nuclear materials A1 and A2 are LiCo0.998Al0.001Mg0.0005Ni0.0005O2Particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm, the mass ratio of the core material A1 to the core material A2 being 20: 80; the shell material B1 is Li2MgTiO4SaidThe molecular formula of the positive electrode active material is 0.004Li2MgTiO4·0.996Li0.998Al0.001Mg0.0005Ni0.0005O2The formed positive electrode active material may be defined as (a1+ a2) × B1.
The preparation method of the positive electrode active material comprises the following steps:
(1) adding CoCl2、Al2(SO4)3、MgSO4And dissolving nickel acetate in water solution to obtain solution with Co, Al, Mg and Ni in the molar ratio of 99.75 to 0.125 to 0.0625, wherein Co is mixed with salt2+The concentration of the sodium hydroxide is 1.25mol/L, and concentrated ammonia water and distilled water are selected to be prepared into complexing agent solution according to the volume ratio of 1: 10; selecting a 1.2mol/L sodium carbonate solution as a precipitator solution; injecting a precipitator solution of a solvent 1/3 into the reaction kettle, under the protection of strong stirring action and inert gas, continuously injecting the mixed salt solution, the complexing agent solution and the precipitator solution into the reaction kettle in a parallel flow control flow mode to react, controlling the flow rate to be not more than 200L/h, stirring simultaneously, controlling the stirring speed to be not more than 200rpm, controlling the pH value of a reaction system to be 6-12, and controlling the temperature of the reaction kettle to be 70-80 ℃ in the reaction process; monitoring the concentration of liquid phase ions doped with elements Al, Mg, Ni and Co in a reaction system in real time in the reaction process; repeatedly crystallizing for 3 times by continuous reaction, and centrifuging to obtain Co carbonate (Co Co-doped with Al, Mg and Ni elements)0.9975Al0.00125Mg0.000625Ni0.000625CO3) Calcining the Al, Mg and Ni three-element Co-doped cobalt carbonate in a muffle furnace at 930 ℃ for 10h, and crushing the calcined product to obtain Al, Mg and Ni Co-doped Co with uniformly distributed particles3O4A precursor;
(2) co Co-doped with Al, Mg and Ni prepared in the way3O4Precursor and Li2CO3Mixing, wherein the molar ratio of Li to Co is 100:99.6, physically mixing the above substances, calcining in a muffle furnace at 1035 ℃ for 11h, pulverizing the calcined product,obtaining LiCo with uniformly distributed particles0.998Al0.001Mg0.0005Ni0.0005O2(i.e., particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm);
(3) the prepared core material A (the mass ratio of the core material A1 to the core material A2 is 20:80) is stirred with the A according to the molar ratio of Li to Mg to Ti to A being 0.2:0.4:0.4:99.6, the mixture is uniformly mixed and then placed in a muffle furnace for calcination at 950 ℃ for 8 hours, and then the calcination product is crushed to obtain the positive electrode active substance, wherein the molecular formula of the positive electrode active substance is as follows:
0.004Li2MgTiO4·0.996LiCo0.998Al0.001Mg0.0005Ni0.0005O2。
(4) dispersing the prepared positive electrode active substance, conductive agent Super-P and binder polyvinylidene fluoride (PVDF) in N-methylpyrrolidone (NMP), wherein the proportion of the positive electrode active substance, the conductive agent and the binder is 97%: 1.5%: 1.5 percent. Uniformly stirring to obtain anode slurry, uniformly coating the slurry on the surface of an aluminum foil, baking by a five-section baking oven, rolling, setting the temperature of the five-section baking oven to be 70 ℃, 80 ℃, 95 ℃, 120 ℃ and 120 ℃, baking by five sections, then placing the current collector coated with the anode slurry in a 100 ℃ baking oven for baking for 8 hours, completely volatilizing the dispersing agent of the anode slurry to obtain the current collector coated with an anode coating, rolling the baked current collector, and compacting the current collector with the density of 4.0g/cm3And preparing the positive pole piece.
(5) Preparing a negative pole piece by adopting a conventional negative pole formula, wherein a negative active material comprises artificial graphite (with a particle size D)50: 13 +/-1 mu m, the graphitization degree is 94 +/-0.5 percent, secondary particles and single particles are mixed, wherein the mass percentage of the secondary particles is 50 percent), superconducting carbon black (Super-P), sodium carboxymethylcellulose (CMC) and Styrene Butadiene Rubber (SBR) are mixed to prepare negative electrode slurry, the negative electrode slurry is coated on copper foil with the thickness of 8 mu m and dried, the baking temperature is 100 ℃, the baking is carried out for 4 hours, the rolling is carried out, and the compacted density is 1.65g/cm3The negative electrode plate of (1).
(6) The used diaphragm is a single-sided ceramic and double-sided oily LBG gluing diaphragm; the electrolyte is LiPF6The lithium salt is prepared by taking a mixture of Ethylene Carbonate (EC), Propylene Carbonate (PC) and dimethyl carbonate (DMC) as a solvent, and adding 4% of 1, 3-propylene sultone, 6% of vinylene carbonate, 1% of succinonitrile and 2% of adiponitrile as additives; and winding the positive pole piece, the negative pole piece and the diaphragm to prepare a battery core, packaging the battery core by using an aluminum plastic film, baking the battery core for 36 hours in a nitrogen-protected oven at the temperature of 120 ℃, injecting electrolyte, performing formation sorting and other procedures to finally obtain the soft package lithium ion battery with the capacity of 5 Ah.
Example 2
The other points are different from the example 1 in the following steps:
(1) adding CoCl2、Al2(SO4)3、MgSO4And dissolving nickel acetate in water to prepare a solution with a molar ratio of Co to Al to Mg to Ni of 99.825 to 0.1 to 0.0375, and preparing Co Co-doped with Al, Mg and Ni3O4And (3) precursor.
(2) Co Co-doped with Al, Mg and Ni prepared in the way3O4Precursor and Li2CO3、MgSO4Mixing nickel acetate, Co, Mg, Ni and Ni, wherein the molar ratio of Li to Co is 100:99.6, placing the mixture into a muffle furnace for calcination at 1035 ℃ for 11h after physically mixing, and then crushing the calcination product to obtain LiCo with uniformly distributed particles0.998Al0.001Mg0.0005Ni0.0005O2(i.e., particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm).
The molecular formula of the positive electrode active material is:
0.004Li2MgTiO4·0.996LiCo0.998Al0.001Mg0.0005Ni0.0005O2。
example 3
The other points are different from the example 1 in the following steps:
(1) adding CoCl2Dissolving the mixture by using aqueous solution to prepare Co with uniformly distributed particles3O4A precursor;
(2) mixing the above prepared Co3O4Precursor and Li2CO3、Al2(SO4)3、MgSO4Mixing Co, Al, Mg and Ni in a molar ratio of 0.998:0.001:0.0005:0.0005 and a molar ratio of Li to Co of 100:99.6, physically mixing the above substances, calcining in a muffle furnace at 1035 ℃ for 11h, and pulverizing the calcined product to obtain LiCo with uniformly distributed particles0.998Al0.001Mg0.0005Ni0.0005O2(i.e., particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm).
The molecular formula of the positive electrode active material is:
0.004Li2MgTiO4·0.996LiCo0.998Al0.001Mg0.0005Ni0.0005O2。
example 4
The other points are the same as the example 2, except that the following steps are carried out:
(1) adding CoCl2、Al2(SO4)3、MgSO4Dissolving nickel acetate in water to prepare a solution with a molar ratio of Co to Al to Mg to Ni of 99.94 to 0.05 to 0.005, and preparing the Co Co-doped with Al, Mg and Ni3O4And (3) precursor.
(2) Co Co-doped with Al, Mg and Ni prepared in the way3O4Precursor and Li2CO3、MgSO4Mixing nickel acetate, wherein the molar ratio of Co, Mg and Ni is 0.999:0.002:0.002, and the molar ratio of Li to Co is 100:99.6, physically mixing the materials, placing the mixture into a muffle furnace for calcination at the temperature of 1035 ℃ for 11h, and then crushing calcined products to obtain LiCo with uniformly distributed particles0.999Al0.0005Mg0.00025Ni0.00025O2(i.e., particle diameter D of core Material A150Is 5.5 μmParticle diameter D of core Material A25018.0 μm).
The molecular formula of the positive electrode active material is:
0.004Li2MgTiO4·0.996LiCo0.999Al0.0005Mg0.00025Ni0.00025O2。
example 5
The other points are different from the example 1 in the following steps:
(2) co Co-doped with Al, Mg and Ni prepared in the way3O4Precursor and Li2CO3、Al2(SO4)3、MgSO4Mixing Co, Al, Mg and Ni in a molar ratio of 0.985:0.005:0.005:0.005 and Li to Co in a molar ratio of 100:99.6, calcining the mixture in a muffle furnace at 1035 ℃ for 11h after physically mixing, and crushing the calcined product to obtain LiCo with uniformly distributed particles0.9965Al0.0015Mg0.001Ni0.001O2(i.e., particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm);
(3) the prepared core material A (the mass ratio of the core material A1 to the core material A2 is 20:80) is stirred with the core material A according to the molar ratio of Li to Mg to Ti to A being 0.25:0.5:0.5:99.5, the core material A is uniformly mixed and then placed in a muffle furnace for calcination at 950 ℃ for 8 hours, and then the calcination product is crushed to obtain the positive electrode active substance, wherein the molecular formula of the positive electrode active substance is as follows:
0.005Li2MgTiO4·0.995LiCo0.9965Al0.0015Mg0.001Ni0.001O2。
example 6
The other points are the same as example 5, except that the following steps are carried out:
(3) the prepared core material A (the mass ratio of the core material A1 to the core material A2 is 20:80) is stirred with the core material A according to the molar ratio of Li to Mg to Ti to A being 0.15:0.3:0.3:99.7, the core material A is uniformly mixed and then placed in a muffle furnace for calcination at 950 ℃ for 8 hours, and then the calcination product is crushed to obtain the positive electrode active substance, wherein the molecular formula of the positive electrode active substance is as follows:
0.003Li2MgTiO4·0.997LiCo0.9965Al0.0015Mg0.001Ni0.001O2。
example 7
The other points are the same as example 5, except that the following steps are carried out:
(1) adding CoCl2、Al2(SO4)3、MgSO4Dissolving nickel acetate in water to prepare a solution with a molar ratio of Co to Al to Mg to Ni of 99.81 to 0.13 to 0.03, and preparing the Co Co-doped with Al, Mg and Ni3O4And (3) precursor.
(2) Co Co-doped with Al, Mg and Ni prepared in the way3O4Precursor and Li2CO3、MgSO4Mixing Co, Mg and Ni in a molar ratio of 0.9975:0.003:0.003, wherein the molar ratio of Li to Co is 100:99.6, physically mixing the materials, calcining in a muffle furnace at 1035 ℃ for 11 hours, and crushing the calcined product to obtain LiCo with uniformly distributed particles0.9975Al0.0013Mg0.0006Ni0.0006O2(that is, the particle diameter D50 of the core material A1 was 5.5 μm, and the particle diameter D50 of the core material A2 was 18.0. mu.m).
The molecular formula of the positive electrode active material is:
0.005Li2MgTiO4·0.995LiCo0.9975Al0.0013Mg0.0006Ni0.0006O2。
example 8
The other points are the same as example 5, except that the following steps are carried out:
(3) weighing lithium carbonate, magnesium oxide and titanium oxide according to the molar ratio of Li to Mg to Ti to A1 to A6332 to 0.45 to 0.9 to 99.1, stirring, uniformly mixing, calcining in a muffle furnace at 950 ℃ for 8h, and then subjecting the core material A1 to calcinationCrushing the calcined product to obtain a positive electrode active material 0.009Li2MgTiO4·0.991LiCo0.9965Al0.0015Mg0.001Ni0.001O2(A1×B1)；
Weighing lithium carbonate, magnesium oxide and titanium oxide according to the molar ratio of Li to Mg to Ti to A2 to be 0.2 to 0.4 to 99.6, stirring the lithium carbonate, the magnesium oxide and the titanium oxide with the nuclear material A2, uniformly mixing, then placing the mixture into a muffle furnace for calcination at the calcination temperature of 950 ℃ for 8 hours, and then crushing the calcined product to obtain a positive electrode active substance 0.004Li2MgTiO4·0.996LiCo0.9965Al0.0015Mg0.001Ni0.001O2(A2×B2)；
Two positive electrode active materials A1 XB 1 and A2 XB 2 are mixed according to the mass ratio of 20:80 and stirred for 4 hours.
Example 9
The other points are the same as example 5, except that the following steps are carried out:
(3) the mass ratio of the core material a1 to the core material a2 was 10: 90.
Example 10
The other points are the same as example 5, except that the following steps are carried out:
(3) the mass ratio of the core material a1 to the core material a2 was 30: 70.
Example 11
The other points are the same as example 5, except that the following steps are carried out:
(3) the nuclear material a prepared as described above (mass ratio of the nuclear material a1 to the nuclear material a2 was 20:80) was subjected to AlF extraction at a molar ratio of Al: a of 0.5:99.53Stirring with the A, uniformly mixing, calcining in a muffle furnace at 950 deg.C for 8 hr, and pulverizing to obtain positive active material with molecular formula of 0.005AlF3·0.995LiCo0.9965Al0.0015Mg0.001Ni0.001O2。
Example 12
The other points are the same as example 5, except that the following steps are carried out:
(3) mixing the aboveThe prepared core material a (mass ratio of the core material a1 to the core material a2 was 20:80) was prepared by weighing lithium carbonate, magnesium oxide, titanium oxide, and AlF in a molar ratio of Li: Mg: Ti: Al: a ═ 0.1:0.2:0.2:0.3:99.53Stirring the mixture and the A, uniformly mixing, then placing the mixture in a muffle furnace for calcining at 950 ℃ for 8 hours, and then crushing a calcined product to obtain a positive active substance which is in a (A1+ A2) x (B1+ B2) combination mode and has a molecular formula as follows:
0.002Li2MgTiO4·0.003AlF3·0.995LiCo0.9965Al0.0015Mg0.001Ni0.001O2。
comparative example 1
The positive active material comprises core materials A1 and A2, and the core materials A1 and A2 are LiCoO2Particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm, and the mass ratio of the core material A1 to the core material A2 was 20: 80.
The preparation method of the positive electrode active material comprises the following steps:
adding CoCl2Dissolving in aqueous solution, wherein Co is contained in the mixed salt2+The concentration of the sodium hydroxide is 1.25mol/L, and concentrated ammonia water and distilled water are selected to be prepared into complexing agent solution according to the volume ratio of 1: 10; selecting a 1.2mol/L sodium carbonate solution as a precipitator solution; injecting a precipitator solution of a solvent 1/3 into the reaction kettle, under the protection of strong stirring action and inert gas, continuously injecting the mixed salt solution, the complexing agent solution and the precipitator solution into the reaction kettle in a parallel flow control flow mode to react, controlling the flow rate to be not more than 200L/h, stirring simultaneously, controlling the stirring speed to be not more than 200rpm, controlling the pH value of a reaction system to be 6-12, and controlling the temperature of the reaction kettle to be 70-80 ℃ in the reaction process; monitoring the concentration of liquid phase ions doped with Co in a reaction system in real time in the reaction process; repeated crystallization for 3 times in continuous reaction, and centrifugal filtration to obtain cobalt carbonate (CoCO)3) Calcining the cobalt carbonate in a muffle furnace at 930 ℃ for 10 hours, and then crushing the calcined product to obtain Co with uniformly distributed particles3O4A precursor;
mixing the above prepared Co3O4Precursor and Li2CO3Mixing, wherein the molar ratio of Li to Co is 100:99.6, physically mixing the materials, calcining in a muffle furnace at 1035 ℃ for 11h, and crushing the calcined product to obtain LiCoO with uniformly distributed particles2(i.e., particle diameter D of core Material A1505.5 μm, particle diameter D of core Material A25018.0 μm), the LiCoO prepared above was added2As a positive electrode active material.
In the above examples, the positive electrode active materials of examples 1 to 4 were used in a battery system of 3.0 to 4.35V (to graphite potential); the positive electrode active materials of examples 5 to 12 were used in a battery system of 3.0 to 4.4V (to graphite potential). The positive active material of comparative example 1 was used in a battery system of 3.0 to 4.35V (to graphite potential) or 3.0 to 4.4V (to graphite potential).
The batteries obtained in examples 1 to 12 and comparative example 1 were tested, and the test results are shown in table 1, table 2 and fig. 1 to 9:
TABLE 14.35V (vs. graphite potential) System Performance
Figure BDA0002644965740000161
TABLE 24.4 summary of the Performance of the V (vs. graphite potential) system
Figure BDA0002644965740000171
As can be seen from tables 1 and 2: the performance of the lithium ion battery using the invention is obviously improved. The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations and simplifications are intended to be included in the scope of the present invention.
The batteries prepared in the above examples and comparative examples were characterized as follows:
(1) high temperature storage Property
In the case of 100% SOC, stored at 60 ℃ and 70 ℃ respectively for a defined time, the test results are shown in the table:
the data of 35 days of storage at 60 ℃ show that both example 1 and example 2 in the present invention show relatively excellent high temperature storage performance under the 4.35V system, and particularly, the thickness expansion rate of the battery of example 1 is 3.42% and the thickness expansion rate of the battery of comparative example 1 reaches 7.62% after 35 days of storage at 60 ℃ compared with that of comparative example 1; comparing the data stored at 70 ℃ for 48h, the battery showed the same trend, and the residual capacity after storage of comparative example 1 was 80.75%, whereas the residual capacity of examples 1 and 2 was increased to more than 88% and the overall increase was more than 3% after the improvement of the present invention. Meanwhile, compared with the test results of the embodiment 1, the embodiment 2 and the embodiment 3, the three doping modes have certain influence on the high-temperature performance of the material, the doping elements are all added in the precursor bulk phase and are added in bulk phase and in one firing mode, the influence on the material performance is not large, the two schemes show the same experimental result, and for the embodiment 3, all the doping elements are added in the calcining process, so that the high-temperature performance is poor. Therefore, it is further illustrated that the thermal stability of the positive active material can be effectively improved by precursor bulk phase doping.
The test result under the 4.4V system is the same as the test result under the 4.35V system, which shows that the modification method of the invention effectively improves the storage performance of the battery. Meanwhile, in the comparative example 5 and the example 6, after the battery is stored at 70 ℃ for 48 hours, the residual capacity of the battery is obviously different, specifically, the residual capacity of the battery corresponding to the example 5 reaches over 87 percent after the battery is stored, and the residual capacity of the battery corresponding to the example 6 is only 84 percent, which shows that the material surface coating plays a crucial role in the storage process. Example 5 shows that adjusting the ratio of the large and small particles in the lithium cobaltate material greatly affects the performance of the material compared with examples 9 and 10, because the small particles have smaller particle size and larger specific surface area, and the side reaction with the electrolyte is more severe, therefore, the storage performance of the battery is obviously deteriorated after increasing the ratio of the small particles.
(2) Circulation at 45 deg.C
The batteries obtained in the above examples and comparative examples were subjected to charge and discharge cycles 500 times at 45 ℃ at a charge and discharge rate of 1C/1C and a charge and discharge cutoff voltage of 3.0V to 4.35V (or 3.0V to 4.4V), and the cycle discharge capacity was recorded and divided by the discharge capacity of the 1 st cycle to obtain the capacity retention ratio.
According to the test method, the above cycle test data is obtained, the capacity retention rate is 92.28% after example 1 is cycled for 500 times under the system of 4.35V, and the retention rate is only 87.32% after comparative example 1 is cycled for 500T under the condition, through the modification means of the technical scheme, after the system of 4.35V is cycled for 500T, the capacity retention rate is improved by 5% compared with the unmodified lithium cobaltate material, and for example 4, after the total amount of the modified doping elements is reduced from 2000ppm to 1000ppm, the cycle retention rate is reduced to 89.12%, which is reduced by 3% compared with the cycle performance of example 1, but is still improved by 2% compared with comparative example 1. Meanwhile, the different doping modes have influence on the cycle performance of the anode material, and particularly, the cycle performance of a sample containing the precursor bulk phase doping is better.
Under a 4.4V system, the same rule is found, the cathode material subjected to modification treatment of the invention shows excellent high-temperature cycle performance, the capacity retention rate of comparative example 1 is attenuated to 76.08% after the cathode material is cycled for 500 times under the 4.4V system, and for the preferred example 5 in the invention, the capacity retention rate is still over 90% after the cathode material is cycled for 500 times, and is improved by nearly 14%; comparing example 9 with example 10, adjusting the grading ratio of different sized particles has a more significant effect on the high temperature performance of the battery, specifically, as the ratio of small particles increases, the cycle performance becomes weaker, because the specific surface area of the small particle part is larger, the side reaction with the electrolyte is more significant, which affects the high temperature performance of the battery to a great extent; the two groups of samples of example 5 and example 6 have different coating amounts, and the test results show that the coating modification also influences the cycle performance of the battery to a great extent; compared with the embodiment 7, the embodiment 5 has the advantages that the total amount of doping elements is reduced by 1000ppm, the retention rate of the circulation capacity is reduced by 4%, and the circulation stability of the material is obviously improved along with the improvement of the doping amount; the embodiment 5 is different from the embodiment 8 in the coating mode, and the experimental result shows that the coating modes have equivalent influence on the high-temperature stability of the material and have no relatively obvious difference; the cycle stability of example 11 was slightly inferior, and the capacity retention after 500T cycles was reduced by 1.5% as compared with example 5, which shows that the coating layer on the surface of the active material is different and has a great effect on the thermal stability of the active material. Therefore, in the technical scheme, the anode material has excellent cycle performance under the combined action of bulk phase doping, primary sintering doping and secondary sintering coating.
(3)DSC
And (3) carrying out DSC tests on the battery before and after circulation, and recording exothermic peak positions of the DSC tests of the positive pole piece before and after circulation. Generally, when the lithium cobaltate material is subjected to DSC test in a full-electricity state, 1-2 exothermic peaks appear, and the initial temperature of the exothermic peak of the modified lithium cobaltate material is obviously shifted backwards, which indicates that the thermal stability of the positive electrode material is good. The results of DSC data tested for the 4.35V system show that: for example 1, the DSC exothermic peak initial temperature of the initial fresh fully charged positive electrode sheet test is 302.83 ℃, the DSC test is performed on the positive electrode after 500T cycling, and the test result shows that the exothermic peak position of the DSC of the positive electrode sheet after cycling is 294.23 ℃, 8.6 ℃ is shifted to the low temperature region, while the DSC exothermic peak temperature of the fresh positive electrode sheet of comparative example 1 is 275.92 ℃, which shows that the thermal stability of the positive electrode material prepared in example 1 is significantly better than that of the pure lithium cobaltate material of comparative example 1, and the DSC test result of the positive electrode sheet of comparative example 1 after 500T cycling shows that the exothermic peak temperature of the positive electrode material after cycling is 240.74 ℃, and the initial temperature is changed by 35.18 ℃ compared with that before cycling. The test results of the remaining examples and comparative examples are consistent with the cycle performance results mentioned earlier.
Comparing the data of the 4.4V system shows the same test result as the 4.35V system. The research finds that: for a system with the voltage lower than 4.45V (excluding 4.45V, for a graphite cathode), along with the circulation, the thermal stability of the cathode material gradually becomes worse, which can be in one-to-one correspondence with the capacity attenuation in the circulation process, meanwhile, the thermal stability of the material of the modified lithium cobaltate cathode material prepared by the technical scheme is obviously better, in the technical scheme, the key point of the preparation is that the cathode active substance is enabled to reach the optimal performance: the precursor is doped in bulk phase, some related elements are doped in the first sintering process, and a certain amount of coating is carried out in the second sintering process.
The invention relates to a method and a device for modifying an active substance of a positive electrode, wherein the lithium cobaltate positive electrode material modified by the technical scheme can effectively improve the cycle stability of a battery under a high-voltage system, and meanwhile, certain analysis is carried out on the battery before and after the cycle, and the test result shows that the exothermic peak position of the positive electrode powder DSC is obviously advanced after the cycle of 2.5V-4.45V (for a graphite electrode, 4.45V is not included), which further shows that the structural stability of the positive electrode material is obviously reduced along with the cycle, and meanwhile, the test result also shows that the peak position moving amplitude of the exothermic peak of the lithium cobaltate material after the cycle is smaller than that of a conventional group after the modified and pure lithium cobaltate material is subjected to doping coating modification. This also further shows that the cycle stability of the positive electrode lithium cobalt oxide active material is improved by the modification means of the technical scheme.
The embodiments of the present invention have been described above. However, the present invention is not limited to the above embodiment. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. A positive electrode active material comprises at least one core material and at least one shell material, wherein the at least one shell material is coated on the surface of the at least one core material to form at least one particle with a core-shell structure;
the composition of the at least one core material is the same or different and is selected from Li independently of one anotherxMe1-yMyO2Wherein Me is Co1-a-bAlaZbM is one or more of Al, Mg, Ti, Zr, Co, Ni, Mn, Y, La, Sr, W and Sc, and Z is one or more of Mg, Ti, Zr, Co, Ni and Mn; x is more than or equal to 0.95 and less than or equal to 1.05, y is more than or equal to 0 and less than or equal to 0.1, a is more than or equal to 0 and less than or equal to 0.2, and b is more than or equal to 0 and less than or equal to 0.1;
the composition of the at least one shell material is the same or different and is independently selected from one or more of metal fluorides, metal oxides, metal borate compounds, and metal phosphate compounds.
2. The positive electrode active material according to claim 1, wherein the positive electrode active material comprises two core materials and a shell material, and the shell material is coated on the surfaces of the two core materials to form a particle with a core-shell structure; that is, the formed positive active material may be defined as (a1+ a2) × B1, where a1 and a2 represent two core materials different in composition, and B1 represents a shell material;
or the positive active substance comprises two core materials and two shell materials, wherein one shell material is coated on the surface of one core material to form a particle with a core-shell structure, and the other shell material is coated on the surface of the other core material to form another particle with a core-shell structure; that is, the formed positive active material may be defined as a1 × B1+ a2 × B2, where a1 and a2 represent two core materials having different compositions, B1 and B2 represent two shell materials having different compositions, and a1 × B1+ a2 × B2 is the formed two particles having a core-shell structure.
3. The positive electrode active material according to claim 1 or 2, wherein the particle diameter D of the positive electrode active material509.0 to 14.0 μm.
4. The positive electrode active material according to any one of claims 1 to 3, wherein the positive electrode active material may be composed of active materials having the same particle size or may be composed of active materials having the same particle sizeIs obtained by grading large-particle active substance and small-particle active substance, wherein the particle diameter D of the large-particle active substance50A particle diameter D of the active material of 8.0 to 18.0 μm in small particles502.0 to 6.0 μm.
5. The positive electrode active material according to any one of claims 1 to 4, wherein the thickness of the shell material in the positive electrode active material is ≦ 40nm, such as 5 to 30 nm.
6. The positive electrode active material according to any one of claims 1 to 5, wherein the mass of the shell material in the positive electrode active material is 0.03 to 0.5% of the total mass of the positive electrode active material.
7. A positive plate, comprising the positive active material, a conductive agent and a binder according to any one of claims 1 to 6, wherein the positive plate comprises the following components in percentage by mass:
70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent and 0.5-15 wt% of binder.
8. The positive electrode sheet according to claim 7, wherein said positive electrode sheet has at least one of the following properties:
(i) the DSC exothermic peak initial temperature before circulation is more than or equal to 270 ℃;
(ii) the DSC exothermic peak initial temperature after 500 cycles of circulation at the temperature of 45 ℃ and the charge-discharge rate of 1C/1C is more than or equal to 265 ℃;
(iii) the DSC exothermic peak initial temperature difference before and after 500 cycles of circulation at the charge-discharge rate of 45 ℃ and 1C/1C is less than or equal to 15 ℃.
9. A lithium ion battery comprising the positive electrode sheet according to claim 7 or 8.
10. The lithium ion battery of claim 9, wherein the lithium ion battery has at least one of:
(1) the thickness expansion rate of the battery after 35 days of storage at 60 ℃ is less than or equal to 7 percent;
(2) the residual capacity of the battery after 48 hours of storage at 70 ℃ is more than or equal to 83 percent;
(3) the capacity retention rate is more than or equal to 85 percent after 500 cycles under the charge-discharge multiplying power of 1C/1C at 45 ℃.
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CN115036459A (en) * 2021-03-05 2022-09-09 珠海冠宇电池股份有限公司 Positive active material and lithium ion battery comprising same
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