CN114899399B - Carbon coating method of ternary cathode material with PVDF (polyvinylidene fluoride) as carbon source - Google Patents

Carbon coating method of ternary cathode material with PVDF (polyvinylidene fluoride) as carbon source Download PDF

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CN114899399B
CN114899399B CN202210492150.3A CN202210492150A CN114899399B CN 114899399 B CN114899399 B CN 114899399B CN 202210492150 A CN202210492150 A CN 202210492150A CN 114899399 B CN114899399 B CN 114899399B
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cathode material
ternary cathode
pvdf
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CN114899399A (en
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代德明
龙沧海
王浩
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Wuhan Chuneng New Energy 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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a carbon coating method of a ternary cathode material with PVDF as a carbon source, which comprises the following steps: firstly, uniformly mixing a ternary cathode material precursor with a lithium source, then sintering in an oxygen atmosphere to obtain a ternary cathode material substrate, crushing and screening the ternary cathode material substrate, adding NMP (N-methyl pyrrolidone) to obtain a suspension, adding PVDF powder into NMP, stirring and dissolving to obtain a PVDF solution, pouring the PVDF solution into the suspension, dispersing uniformly, removing bubbles, performing solid-liquid separation to obtain a suspended substance, adding water into the suspended substance, heating, keeping the temperature and stirring, filtering, drying in vacuum, sieving to obtain a pre-coated product, and sintering the pre-coated product in an inert gas atmosphere to obtain the carbon-coated ternary cathode material. The coating method has simple steps, the residual alkali of the substrate material defluorinates the PVDF, so that the electrical property of the coating material is improved, and meanwhile, the PVDF forms a porous structure after carbonization, so that the specific surface area can be improved, and the electrical property can be further improved.

Description

Carbon coating method of ternary cathode material with PVDF (polyvinylidene fluoride) as carbon source
Technical Field
The invention relates to the technical field of coating of lithium battery anode materials, in particular to a carbon coating method of a ternary anode material with PVDF as a carbon source.
Background
The lithium ion battery as a clean energy storage device has the characteristics of high specific capacity, high voltage and good safety, and is widely applied to the fields of portable electronic products, power automobiles, power generation and energy storage, electric tools and the like. Since the positive electrode material provides faraday current, which is a basic component of an electrochemical energy storage system, and the development and research thereof have a large space, the research on the positive electrode material has been paid much attention compared with the rest of the battery. Common lithium ion battery positive electrode materials include lithium cobaltate, lithium nickel cobalt manganese oxide, lithium manganese oxide, and the like. The ternary layered oxide nickel cobalt lithium manganate has the comprehensive advantages of high theoretical specific capacity and low cost, so that the ternary layered oxide nickel cobalt lithium manganate becomes a research hotspot of the high-energy-density lithium ion battery anode material.
However, the nickel cobalt lithium manganate of the ternary layered oxide has strong oxidizing property, and is easy to react with electrolyte, so that potential safety hazards are caused; its polycrystalline material itself is also prone to internal microcracking and even pulverization during cycling resulting in a large decay in capacity, and the material has limited electronic conductivity, insufficient to activate all chemical energy to provide a faraday current. Therefore, it is necessary to protect the surface of these material particles and to improve the electronic conductivity thereof. Coating is widely used as a surface modification method, wherein fast ion conductors and metal oxides are used as coating materials, but the dry coating-based processes have difficulty in meeting the requirements on coating uniformity and electronic conductivity.
In view of the above, it is necessary to develop a wet coating method suitable for industrial production to improve the electron conductivity of the ternary cathode material and reduce the probability of failure of microcracks of the cathode.
Disclosure of Invention
In view of the above, the invention provides a carbon coating method for a ternary cathode material using PVDF as a carbon source.
One of the purposes of the invention is to improve the electrical property of the prior ternary cathode material;
one of the objects of the present invention is to improve the structural stability of the conventional ternary positive electrode material.
In the invention, PVDF is polyvinylidene fluoride, and NMP is N-methyl pyrrolidone.
The technical scheme of the invention is realized as follows: the invention provides a carbon coating method of a ternary cathode material with PVDF as a carbon source, which comprises the following steps:
s1, uniformly mixing a ternary positive material precursor with a lithium source to obtain a first mixture;
s2, sintering and screening the first mixture in an oxygen atmosphere to obtain a ternary cathode material substrate;
s3, crushing and screening the ternary cathode material substrate, adding the crushed ternary cathode material substrate into NMP, and uniformly stirring to obtain a suspension;
s4, adding PVDF powder into NMP, stirring and dissolving to obtain a PVDF solution;
s5, pouring the PVDF solution into the suspension, dispersing uniformly, removing bubbles, and performing solid-liquid separation to obtain a suspended substance;
s6, adding water into the suspended substance, heating, keeping the temperature, stirring, filtering, drying in vacuum, and screening to obtain a pre-coated product;
and S7, sintering the pre-coated product in an inert gas atmosphere to obtain the carbon-coated ternary cathode material.
On the basis of the above technical solution, preferably, the precursor of the ternary cathode material is an alloy, hydroxide or salt of three elements of lithium, nickel, cobalt and manganese.
On the basis of the above technical solution, preferably, the chemical formula of the ternary cathode material substrate is LiNi 1-x- y Co x Mn y O 2 、LiNi 1-x-y Co x Al y O 2 And LiNi 1-x-y Mn x Al y O 2 Wherein x is more than 0 and less than 0.5, and y is more than 0 and less than 0.5.
Based on the above technical solution, preferably, in step S1, the stoichiometric ratio of the lithium element in the lithium source to the transition metal element in the ternary cathode material precursor is (1.02-1.15): 1.
in addition to the above technical solution, preferably, in step S1, the lithium source is lithium hydroxide.
On the basis of the above technical solution, preferably, in step S2, the content of 0 < hydroxyl < 5% and the content of 0 < carbonate < 5% in the ternary cathode material substrate.
On the basis of the above technical solution, preferably, in step S3, the mass ratio of the ternary cathode material substrate to NMP is 1: (0.5-2).
More preferably, in step S4, the mass ratio of NMP to PVDF is (20-100): 1.
based on the above technical solution, preferably, in step S4, the PVDF has a number average molecular weight of 100000-1200000g/mol.
On the basis of the above technical scheme, preferably, in step S5, the method for dispersing uniformly and removing bubbles is one or more of stirring, ultrasound and vacuum pumping.
On the basis of the technical scheme, preferably, the ultrasonic dispersion time is 5-60min, and the stirring time is 10-50min.
On the basis of the above technical scheme, preferably, in step S5, the method for obtaining the suspended substance is one or a combination of several of filtration, centrifugation, standing for layering, and supernatant liquid pouring.
On the basis of the above technical scheme, preferably, in step S6, the heating temperature is 40-60 ℃, and the heating time is 10-60min.
On the basis of the above technical scheme, preferably, in step S7, the sintering temperature is 500-800 ℃, and the sintering time is 3-8h.
On the basis of the technical scheme, the mass ratio of carbon to transition metal in the final carbon-coated cathode material is 600-5000ppm.
Compared with the prior art, the carbon coating method of the ternary cathode material with PVDF as the carbon source has the following beneficial effects:
(1) According to the carbon coating method of the ternary cathode material, PVDF is uniformly coated on the surface of a substance by using a non-solvent phase transfer method, the swelling behavior of non-solvent water in a high-molecular network structure is used, so that a coating layer naturally has a mesoporous structure, meanwhile, residual alkali of a substrate material is used for performing defluorination pretreatment on the PVDF to a certain extent, and then, a conductive carbon material is sintered and synthesized in situ, so that the obtained material has higher electronic conductivity and structural stability, and the multiplying power performance, the cycle performance and the safety performance of a button cell assembled by the material are improved; (2) According to the invention, the carbon coating material is obtained by carbonizing PVDF through secondary sintering, rich micropores are formed in the decomposition process of PVDF, and finally the porous conductive carbon material is obtained.
(3) The coating method provided by the invention can be used for wrapping and constraining the ternary cathode material to a certain extent, and has the effect of ring joint microcrack risk on the polycrystalline secondary ball material.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, are within the scope of the present invention.
Example 1
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 900 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 4 hours, and screening to obtain a ternary cathode material substrate with a chemical formula LiNi 0.9 Co 0.05 Mn 0.05 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.4%, and the content of carbonate is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:0.5, and mixing uniformly to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
And mixing the PVDF solution and the suspension according to the volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 50 ℃, preserving heat, stirring for 30min, filtering, transferring to a vacuum drying oven for drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 720 ℃ in a nitrogen atmosphere, and sintering for 5 hours to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was detected to be 2000ppm.
Example 2
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the aluminum element is 1.02.
Heating the precursor to 900 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 4 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.9 Co 0.03 Al 0.07 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:0.5, and mixing uniformly to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
And (3) mixing the PVDF solution with the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating to 50 ℃ in water bath, carrying out heat preservation and stirring treatment for 30min, filtering, transferring to a vacuum drying oven for drying treatment, drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 720 ℃ in a nitrogen atmosphere, and sintering for 5h to obtain the carbon-coated ternary cathode material. Detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 2000ppm.
Example 3
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the manganese element and the aluminum element is 1.1.
Heating the precursor to 900 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 4 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.9 Mn 0.04 Al 0.06 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.4 percent, and carbon is containedThe acid radical content is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:0.5, and mixing uniformly to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
And mixing the PVDF solution and the suspension according to the volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 50 ℃, preserving heat, stirring for 30min, filtering, transferring to a vacuum drying oven for drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 720 ℃ in a nitrogen atmosphere, and sintering for 5h to obtain the carbon-coated ternary cathode material. Detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 2000ppm.
Example 4
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.02.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate with a chemical formula LiNi 0.9 Co 0.06 Mn 0.04 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.4%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:1, uniformly mixing to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
Mixing the PVDF solution and the suspension according to the volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 50 ℃, preserving heat, stirring for 30min, filtering, transferring to a vacuum drying oven for drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 600 ℃ in a nitrogen atmosphere, and sintering for 6h to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was detected to be 2000ppm.
Example 5
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.1.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.8 Co 0.1 Mn 0.1 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.5%, and the content of carbonate is 0.3%.
Crushing the ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to the mass ratio of 1:1.5, mixing evenly to obtain suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
Mixing the PVDF solution and the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 40 ℃, carrying out heat preservation and stirring treatment for 60min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was detected to be 2000ppm.
Example 6
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.15.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate with a chemical formula LiNi 0.8 Co 0.05 Mn 0.15 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.8%, and the content of carbonate is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:2, uniformly mixing to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 100000g/mol and NMP according to the mass ratio of 1.
Mixing the PVDF solution and the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 60 ℃, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. Detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 2000ppm.
Example 7
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 08 Co 015 Mn 005 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:2, uniformly mixing to obtain a suspension.
And uniformly mixing PVDF with the number average molecular weight of 200000g/mol and NMP according to the mass ratio of 1.
And mixing the PVDF solution and the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 60 ℃, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was detected to be 1800ppm.
Example 8
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.85 Co 0.1 Mn 0.05 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing the ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to the mass ratio of 1:2, mixing evenly to obtain suspension.
And uniformly mixing the PVDF with the number average molecular weight of 500000g/mol and NMP according to the mass ratio of 1.
And (3) mixing the PVDF solution with the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 60 ℃, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. And detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 1600ppm.
Example 9
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.6 Co 0.1 Mn 0.3 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing a ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to a mass ratio of 1:2, uniformly mixing to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 1000000g/mol and NMP according to the mass ratio of 1.
And mixing the PVDF solution and the suspension according to the volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating to 60 ℃ in water bath, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was detected to be 1200ppm.
Example 10
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.6 Co 0.2 Mn 0.2 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing the ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to the mass ratio of 1:2, mixing evenly to obtain suspension.
And uniformly mixing the PVDF with the number average molecular weight of 1200000g/mol and NMP according to the mass ratio of 1.
And (3) mixing the PVDF solution with the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating to 60 ℃ in water bath, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, drying, and screening to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8 hours to obtain the carbon-coated ternary cathode material. Detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 800ppm.
Example 11
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate with a chemical formula LiNi 0.6 Co 0.3 Mn 0.1 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing the ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to the mass ratio of 1:2, uniformly mixing to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 500000g/mol and NMP according to the mass ratio of 1.
And mixing the PVDF solution and the suspension according to the volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 60 ℃, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. The mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material was determined to be 1400ppm.
Example 12
The precursor obtained by purchasing is adopted, wherein the stoichiometric ratio of the lithium element to the sum of the nickel element, the cobalt element and the manganese element is 1.05.
Heating the precursor to 800 ℃ in an oxygen atmosphere, carrying out heat preservation treatment for 5 hours, and screening to obtain a ternary cathode material substrate, wherein the chemical formula of the ternary cathode material substrate is LiNi 0.65 Co 0.25 Mn 0.1 O 2 In the ternary cathode material substrate, the content of hydroxyl is 0.3%, and the content of carbonate is 0.3%.
Crushing the ternary cathode material substrate, then screening, and mixing the screened ternary cathode material substrate with NMP according to the mass ratio of 1:2, uniformly mixing to obtain a suspension.
And uniformly mixing the PVDF with the number average molecular weight of 500000g/mol and NMP according to the mass ratio of 1.
And (3) mixing the PVDF solution with the suspension according to a volume ratio of 3.
Adding water into the suspended matter until the suspended matter can be immersed, heating in water bath to 60 ℃, carrying out heat preservation and stirring treatment for 10min, filtering, transferring to a vacuum drying oven for drying treatment, and screening after drying to obtain a pre-coated product.
And heating the pre-coated product to 500 ℃ in a nitrogen atmosphere, and sintering for 8h to obtain the carbon-coated ternary cathode material. Detecting that the mass ratio of the carbon element to the transition metal in the carbon-coated ternary cathode material is 1200ppm.
Comparative example
The lithium nickel cobalt manganese oxide anode material purchased from the market is adopted.
The positive electrode materials prepared in the above examples and comparative examples were subjected to physical and chemical property tests, and the residual alkali, the specific surface area, the electronic conductivity, and the capacity of the battery prepared using the positive electrode material were respectively detected.
Specific data results are shown in the following table:
Figure GDA0004007725140000141
Figure GDA0004007725140000151
compared with the conventional ternary cathode material, the ternary cathode material prepared by the coating method of the invention not only reduces the residual alkali amount, but also has larger specific surface area than the commercially available material, because PVDF is used as the coating material, the PVDF consumes the residual alkali on one hand to obtain mesopores, and on the other hand, pores appear on the surface of the PVDF due to the decomposition effect of heating in the later carbonization process. .
The cycle performance tests were also performed on the batteries prepared from the positive electrode materials of examples 1 to 12 and comparative example, and the results were as follows:
Figure GDA0004007725140000152
obviously, compared with the commercially available ternary cathode material, the ternary cathode material obtained by coating by the method has better cycle performance, and a conclusion cannot be easily drawn.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (9)

1. A carbon coating method of a ternary cathode material with PVDF as a carbon source is characterized by comprising the following steps:
s1, uniformly mixing a ternary positive material precursor with a lithium source to obtain a first mixture; the chemical formula of the ternary cathode material substrate is LiNi 1-x-y Co x Mn y O 2 、LiNi 1-x-y Co x Al y O 2 And LiNi 1-x-y Mn x Al y O 2 Wherein x is more than 0 and less than 0.5, y is more than 0 and less than 0.5;
s2, sintering and screening the first mixture in an oxygen atmosphere to obtain a ternary cathode material substrate, wherein the sum of the contents of hydroxyl and carbonate in the ternary cathode material substrate is more than 0 and less than 5 percent;
s3, crushing and screening the ternary cathode material substrate, adding the crushed ternary cathode material substrate into NMP, and uniformly stirring to obtain a suspension;
s4, adding PVDF powder into NMP, stirring and dissolving to obtain a PVDF solution;
s5, pouring the PVDF solution into the suspension, dispersing uniformly, removing bubbles, and performing solid-liquid separation to obtain a suspended substance;
s6, adding water into the suspended substance, heating, keeping the temperature, stirring, filtering, drying in vacuum, and screening to obtain a pre-coated product;
and S7, sintering the pre-coated product in an inert gas atmosphere to obtain the carbon-coated ternary cathode material.
2. The method for carbon coating of the ternary cathode material with PVDF as a carbon source according to claim 1, wherein in step S1, the stoichiometric ratio of the lithium element in the lithium source to the transition metal element in the precursor of the ternary cathode material is (1.02-1.15): 1.
3. the method for carbon coating of the ternary cathode material with PVDF as a carbon source in claim 1, wherein in step S3, the mass ratio of the ternary cathode material substrate to NMP is 1: (0.5-2).
4. The method for carbon-coating a ternary cathode material with PVDF as a carbon source in claim 1, wherein the mass ratio of NMP to PVDF in step S4 is (20-100): 1.
5. the method for carbon-coating a ternary positive electrode material using PVDF as a carbon source in claim 1, wherein the number-average molecular weight of PVDF in step S4 is 100000-1200000g/mol.
6. The carbon coating method of the PVDF ternary cathode material as a carbon source in the step S5, wherein the method for uniformly dispersing and removing bubbles is one or more of stirring, ultrasound and vacuum pumping.
7. The carbon coating method of the PVDF ternary cathode material as the carbon source in the claim 1, wherein the method for obtaining the suspended substance in the step S5 is one or a combination of filtering, centrifuging, standing for layering and removing the supernatant.
8. The method for carbon coating of a ternary cathode material with PVDF as a carbon source in claim 1, wherein the heating temperature is 40-60 ℃ and the heating time is 10-60min in step S6.
9. The method for carbon coating of the PVDF ternary cathode material as the carbon source in the claim 1, wherein in the step S7, the sintering temperature is 500-800 ℃, and the sintering time is 3-8h.
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