CN115632124B - High-nickel ternary cathode material, preparation method thereof and lithium ion battery - Google Patents

High-nickel ternary cathode material, preparation method thereof and lithium ion battery Download PDF

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CN115632124B
CN115632124B CN202211652343.7A CN202211652343A CN115632124B CN 115632124 B CN115632124 B CN 115632124B CN 202211652343 A CN202211652343 A CN 202211652343A CN 115632124 B CN115632124 B CN 115632124B
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iron phosphate
polyacrylonitrile
lithium iron
mixed solution
ternary
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CN115632124A (en
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范未峰
雷英
罗涵钰
罗明洋
张彬
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Yibin Libao New Materials Co Ltd
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    • H—ELECTRICITY
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    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
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    • C01G53/40—Nickelates
    • C01G53/42—Nickelates containing alkali metals, e.g. LiNiO2
    • C01G53/44—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese
    • C01G53/50—Nickelates containing alkali metals, e.g. LiNiO2 containing manganese of the type [MnO2]n-, e.g. Li(NixMn1-x)O2, Li(MyNixMn1-x-y)O2
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    • 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
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    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
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    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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Abstract

The invention discloses a high-nickel ternary cathode material, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries. By utilizing the lone pair electrons contained on the nitrogen atom of the CN-group in Polyacrylonitrile (PAN) and easily forming coordination bonds with metal ions, through introducing PAN with metal chelating property as a molecular bridging agent, based on the coordination property of CN and metal in PAN, liNi is prepared x Co y Mn 1‑x‑y O 2 And is closely pulled together with the lithium iron phosphate molecules of the surface coating layer. The introduction of the lithium iron phosphate by adopting the mode provided by the invention is favorable forThe uniformity of lithium iron phosphate distribution is improved, and the electrochemical performance and the cycling stability of the high-nickel ternary cathode material can be obviously improved.

Description

High-nickel ternary cathode material, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a high-nickel ternary cathode material, a preparation method thereof and a lithium ion battery.
Background
Layered oxide LiNixCoyMn1-x-yO 2 (NCM), such as NCM811, due to its higher theoretical specific capacity (about 280 mAh g −1 ) And high working voltage, and is a positive electrode material for the extensive research and application of batteries for electric vehicles. The performance of the material is closely related to the Ni content, the higher the Ni content is, the larger the specific capacity is, but the safety performance is seriously deteriorated. It is therefore of great importance to improve the safety properties of nickel-rich NCM materials without affecting their electrochemical properties, in particular the energy density of the battery. During thermal runaway of an NCM cell, a series of exothermic reactions occur within the cell's internal components, with the release of oxygen from the NCM caused by phase change being a critical step. In addition, the electrolyte is in direct contact with the surface of the material, and the phase change of the NCM is accelerated by the electrolyte in the charge and discharge processes. For this reason, the development of different oxide coatings to surface coat the active NCM material may prevent its reaction with the electrolyte. However, these coatings have significantly limited rate capability of coating modified NCM cathode materials because of limited ionic and electronic conductivity. The inactive coating material also reduces the energy density of the overall battery. Therefore, it is a challenge how to balance safety and performance by adjusting the coating thickness.
Lithium iron phosphate (LFP) has an olivine structure and has high safety and stability. The theoretical capacity can reach 170 mAh g −1 . Therefore, by controlling a certain blending ratio, the LFP is blended with the NCM to use the energy density of the obtained battery at a level substantially equivalent to that of the NCM battery. Direct conversion of LiNi in CN104779377A 1/3 Co 1/3 Mn 1/3 O 2 The lithium iron phosphate anode material is mixed with a lithium iron phosphate anode material by a dry method and is matched with a lithium titanate cathode for use, and the safety of the obtained battery is obviously improved. Chenjun super et al adopts dry method fusion method to mix LiFePO with LiFePO 4 The nano particles are mixed and coated on the LiNi as a coating 0.8 Co 0.15 Al 0.05 O 2 Surface, liFePO 4 The coating helps to reduce the formation of the cathode-electrolyte interface. And LiNi 0.8 Co 0.15 Al 0.05 O 2 In contrast, liNi when charged to 4.5V 0.8 Co 0.15 Al 0.05 O 2 With LiFePO 4 The composite cathode material has higher reversible capacity of 210 mAh -1 The capacity retention ratio is more excellent (100 cycles, retention ratio 95%). Differential thermal analysis DSC test also shows that the thermal runaway temperature of the composite cathode material is higher than that of pure LiNi 0.8 Co 0.15 Al 0.05 O 2 And (3) a positive electrode material. Therefore, the LFP is matched with the NCM material for use, which is beneficial to realizing high energy density, circulation stability and high safety performance, and is expected to be applied in a large scale.
At present, the problems of poor uniformity and weak interaction between a high-nickel ternary material and lithium iron phosphate generally exist in a compounding mode of the high-nickel ternary material and the lithium iron phosphate, so that the comprehensive effect of electrochemical properties is not ideal, such as low capacity and rate performance.
In view of this, the invention is particularly proposed.
Disclosure of Invention
The invention aims to provide a high-nickel ternary cathode material, a preparation method thereof and a lithium ion battery, and aims to remarkably improve the electrochemical performance and the cycling stability of the material.
The invention is realized in the following way:
in a first aspect, the invention provides a high-nickel ternary cathode material, which comprises a ternary material body and a coating layer coated on the ternary material body, wherein the coating layer comprises polyacrylonitrile and lithium iron phosphate;
wherein the chemical formula of the ternary material body is LiNi x Co y Mn 1-x-y O 2 ；
0.7＜x＜1.0，0.0＜y＜0.3。
In an optional embodiment of the invention, the mass ratio of polyacrylonitrile to the ternary material body is 0.2-2.
In a second aspect, the invention also provides a preparation method of the high-nickel ternary cathode material, which comprises the following steps: and dispersing the ternary material body, polyacrylonitrile and lithium iron phosphate in a solution system to obtain a mixed dispersion liquid, and carrying out heat treatment on the mixed dispersion liquid to form a coating layer on the ternary material body.
In an alternative embodiment of the invention, the method comprises the following steps: mixing and dissolving polyacrylonitrile and an organic solvent to obtain a first mixed solution, mixing the first mixed solution with a ternary material body to obtain a second mixed solution, and mixing the second mixed solution with lithium iron phosphate to obtain a mixed dispersion solution; treating the mixed dispersion liquid for 12-24 h at the temperature of 100-150 ℃.
In an optional embodiment of the invention, polyacrylonitrile and an organic solvent are mixed and stirred for 2-10 h to obtain a first mixed solution, wherein the concentration of polyacrylonitrile in the first mixed solution is 1-8 wt%.
In an alternative embodiment of the invention, the organic solvent is selected from at least one of N, N-dimethylformamide, N-dimethylacetamide and azomethylpyrrolidone.
In an alternative embodiment of the invention, the molecular weight of polyacrylonitrile is 100000-200000.
In an optional embodiment of the invention, in the preparation of the second mixed solution, the mass ratio of polyacrylonitrile to the ternary material bulk is 0.2-2, and the stirring is carried out for 1-4 h under the condition of 150-500 rpm.
In an optional embodiment of the invention, mixing lithium iron phosphate with the second mixed solution, wherein the mass ratio of the lithium iron phosphate to the ternary material body is 1-9, and stirring for 1-6 h under the condition of 200-500 rpm;
the D50 of the lithium iron phosphate is 100nm-200nm.
In a third aspect, the present invention also provides a lithium ion battery, which is prepared from the high-nickel ternary cathode material in any one of the above embodiments or the high-nickel ternary cathode material prepared by the preparation method in any one of the above embodiments.
The invention has the following beneficial effects: by utilizing the lone pair electrons contained on the nitrogen atom of the CN-group in Polyacrylonitrile (PAN) and easily forming coordination bonds with metal ions, through introducing PAN with metal chelating property as a molecular bridging agent, based on the coordination property of CN and metal in PAN, liNi is prepared x Co y Mn 1-x-y O 2 And the lithium iron phosphate molecules are tightly pulled together with the surface coating layer. The adoption of the method provided by the invention to introduce the lithium iron phosphate is beneficial to improving the uniformity of the distribution of the lithium iron phosphate, and can obviously improve the electrochemical performance and the cycle stability of the high-nickel ternary cathode material.
Drawings
In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings needed to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and for those skilled in the art, other related drawings can be obtained according to the drawings without inventive efforts.
FIG. 1 is an XRD pattern of a sample prepared in example 1;
FIG. 2 is an SEM image of a polymer and a sample before and after LFP coating, where in FIG. 2 a represents before coating and b represents after coating;
FIG. 3 is a first-turn charge-discharge curve at 0.1C magnification;
FIG. 4 is a graph showing the results of 100-cycle stability test of samples obtained in examples and comparative examples.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Polyacrylonitrile (PAN) is obtained by radical polymerization of acrylonitrile monomers. The acrylonitrile units in the macromolecular chain are linked in a linker-to-tail fashion. The lone pair of electrons contained in the nitrogen atom of the CN-group in PAN is apt to form a coordinate bond with a metal ion. The inventors propose to introduce PAN having a metal-chelating property as a molecular bridging agent and to introduce LiNi based on the coordination property of CN in PAN to the metal x Co y Mn 1-x-y O 2 And surface coating layer LiFePO 4 The (LFP) molecules are "pulled" together tightly.
The embodiment of the invention also provides a preparation method of the high-nickel ternary cathode material, which comprises the following steps: and dispersing the ternary material body, polyacrylonitrile and lithium iron phosphate in a solution system to obtain a mixed dispersion liquid, and carrying out heat treatment on the mixed dispersion liquid to form a coating layer on the ternary material body. The solvent can be removed through heat treatment, the polyacrylonitrile and the lithium iron phosphate are utilized to form the coating layer, and the PAN plays a role of a molecular bridging agent in the middle, so that the lithium iron phosphate is tightly combined with the ternary material body and is uniformly distributed, the effect of modifying the lithium iron phosphate is favorably further improved, and the electrochemical performance and the cycling stability of the material are improved.
In the actual operation process, the method comprises the following steps: (1) Mixing and dissolving polyacrylonitrile and an organic solvent to obtain a first mixed solution; (2) Mixing the first mixed solution with a ternary material body (NCM) to obtain a second mixed solution; (3) Mixing the second mixed solution with lithium iron phosphate to obtain a uniformly mixed dispersion solution; (4) Treating the mixed dispersion liquid at 100-150 deg.c for 12-24 hr. Firstly, dissolving polyacrylonitrile, then mixing the polyacrylonitrile with a ternary material body, enabling macromolecular polyacrylonitrile to be wound and adsorbed on the surface of NCM, mixing the polyacrylonitrile with lithium iron phosphate, enabling the lithium iron phosphate to interact with PAN molecules on the surface of NCM, removing an organic solvent through heat treatment, and then forming a PAN-LFP composite coating layer on the surface of the NCM material.
With respect to step (1):
in some embodiments, polyacrylonitrile and the organic solvent are mixed and stirred for 2h to 10h to obtain a uniform first mixed solution, and the stirring time can be 2h, 5h, 7h, 10h and the like, so that polyacrylonitrile is fully dissolved to obtain a transparent viscous solution.
In some embodiments, the organic solvent is selected from at least one of N, N-Dimethylformamide (DMF), N-dimethylacetamide, and N-methylpyrrolidone, and may be any one or more of the above solvents. The concentration of polyacrylonitrile in the first mixed solution is 0.2wt% -2wt%, and if the concentration is too high, the polyacrylonitrile cannot be dissolved sufficiently, and the specific capacity of the material is obviously reduced, and the specific concentration can be 0.2wt%, 0.5wt%, 1wt%, 1.5wt%, 2wt%, and the like.
In some embodiments, the molecular weight of polyacrylonitrile is 100000-200000 (e.g., 100000, 120000, 150000, 200000, etc.), and preferably the molecular weight is in the above range, and too high a molecular weight is not easily dissolved, and too low a molecular weight does not function well as a molecular bridging agent.
With respect to step (2):
in some embodiments, in the preparation of the second mixed solution, the mass ratio of polyacrylonitrile to the ternary material bulk is 0.2-2, the ternary material bulk is added into the solution system, and the mixture is stirred for 1-4 h at 150-500 rpm. By optimizing the dosage of polyacrylonitrile, the comprehensive electrochemical performance of the material is favorably improved.
Specifically, the chemical formula of the ternary material body is LiNi x Co y Mn 1-x-y O 2 (ii) a X is more than 0.7 and less than 1.0, and y is more than 0.0 and less than 0.3. The ternary material body is a commercial material, x can be 0.83, 0.85, 0.90 and the like, y can be 0.05, 0.11, 0.20, 0.25 and the like, and x + y is required to be less than 1.
Specifically, the mass ratio of polyacrylonitrile to the ternary material bulk may be 0.2.
Specifically, the rotation speed of stirring may be 150rpm, 200rpm, 300rpm, 400rpm, 500rpm, etc., and the stirring time may be 1h, 2h, 3h, 4h, etc.
With respect to step (3):
in some embodiments, mixing lithium iron phosphate with the second mixed solution, wherein the mass ratio of the lithium iron phosphate to the ternary material body is 1-9, and stirring for 1-6 h under the condition of 200-500 rpm, so that the lithium iron phosphate is uniformly dispersed and fully interacts with PAN molecules.
Specifically, the mass ratio of the lithium iron phosphate to the ternary material bulk may be 1.
Specifically, the rotation speed of stirring may be 200rpm, 300rpm, 400rpm, 500rpm, etc., and the stirring time may be 1h, 2h, 3h, 4h, 5h, 6h, etc.
In some embodiments, the particle size of the lithium iron phosphate is not too large, the D50 of the lithium iron phosphate is 100nm to 200nm, such as 100nm or 200nm, and the uniformity of the coating is more easily improved by using lithium iron phosphate with a smaller particle size.
With respect to step (4):
putting the mixed solution containing NCM and LFP into a vacuum oven, and drying at 100-150 ℃ for 12-24h to obtain a NCM solid mixture coated by the composite coating, wherein the NCM solid mixture is marked as LFP @ PAN @ NCM.
Specifically, the drying temperature may be 100 ℃, 110 ℃, 120 ℃, 130 ℃, 140 ℃, 150 ℃ and the like, and the drying time may be 12 hours, 15 hours, 20 hours, 24 hours and the like.
The embodiment of the invention also provides a high-nickel ternary cathode material which can be prepared by the preparation method and comprises a ternary material body and a coating layer coated on the ternary material body, wherein the coating layer comprises polyacrylonitrile and lithium iron phosphate; wherein the chemical formula of the ternary material body is LiNi x Co y Mn 1-x-y O 2 ；0.7＜x＜1.0，0.0＜y＜0.3。
PAN having a metal chelating property is introduced as a molecular bridging agent, and LiNi is introduced based on the coordination property of CN to a metal in PAN x Co y Mn 1-x-y O 2 The lithium iron phosphate particles are tightly pulled together with the surface coating layer lithium iron phosphate molecules, so that the uniformity of the distribution of the lithium iron phosphate is improved, and the electrochemical performance and the cycle stability of the high-nickel ternary cathode material can be obviously improved.
In some embodiments, the mass ratio of polyacrylonitrile to the ternary material bulk is 0.2-2, and the mass ratio of lithium iron phosphate to the ternary material bulk is 1.
In some embodiments, the lithium ion battery can be prepared by using the high-nickel ternary cathode material, and the performance of the lithium ion battery can be further improved due to the improvement of the performance of the cathode material.
The features and properties of the present invention are described in further detail below with reference to examples.
Example 1
The embodiment provides a preparation method of a high-nickel ternary cathode material, which comprises the following steps:
(1) Weighing polyacrylonitrile powder (molecular weight of 150000), adding into N, N-Dimethylformamide (DMF) solvent, controlling the amount of the solvent to make the concentration of polyacrylonitrile 0.5wt%, stirring at room temperature for 5h, and dissolving thoroughly to obtain transparent viscous solution.
(2) Weighing commercial high-nickel ternary material LiNi 0.85 Co 0.1 Mn 0.05 O 2 And stirring for 3 hours at the rotating speed of 300rpm, wherein the mass ratio of polyacrylonitrile to the ternary material body is 0.5.
(3) And (3) after the NCM is fully dispersed, weighing a certain amount of lithium iron phosphate (D50 is 100 nm) and adding the lithium iron phosphate into the solution obtained in the step (2), wherein the mass ratio of the lithium iron phosphate to the ternary material body is 1:9, and stirring for 3 hours at the rotating speed of 300 rpm.
(4) And (4) placing the mixed dispersion liquid obtained in the step (3) in a vacuum oven at 120 ℃, and drying for 20 hours to obtain an NCM solid mixture coated by the composite coating, wherein the NCM solid mixture is marked as LFP @ PAN @ NCM.
Example 2
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of polyacrylonitrile to the ternary material body is 1.0.
Example 3
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of polyacrylonitrile to the ternary material body is 0.2.
Example 4
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of the polyacrylonitrile to the ternary material body is 2.0.
Example 5
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Example 6
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Example 7
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Example 8
This example provides a method for preparing a high-nickel ternary cathode material, which is different from example 1 only in that: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Comparative example 1
The comparative example provides a commercial high-nickel ternary cathode material LiNi 0.85 Co 0.1 Mn 0.05 O 2 。
Comparative example 2
The only difference from example 1 is: polyacrylonitrile was replaced with an equal amount of phenolic resin.
Comparative example 3
The only difference from example 1 is: polyacrylonitrile was replaced with an equal amount of polyethylene oxide (PEO).
Comparative example 4
The only difference from example 1 is: polyacrylonitrile was replaced with an equal amount of epoxy resin.
Comparative example 5
The physical mixed sample is obtained by dry mixing and ball milling of NCM and lithium iron phosphate, and the specific type of NCM and the using amount of lithium iron phosphate are the same as those in the embodiment 1.
Comparative example 6
The only difference from example 1 is: the mass ratio of polyacrylonitrile to the ternary material body is 5.0.
Comparative example 7
The only difference from example 1 is: polyacrylonitrile is not added in the preparation process.
Comparative example 8
The only difference from example 1 is: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Comparative example 9
The only difference from example 1 is: the mass ratio of the lithium iron phosphate to the ternary material body is 1.
Test examples
(1) The XRD pattern of the sample prepared in example 1 was measured, and the result is shown in fig. 1.
As can be seen from fig. 1, the diffraction positions of the coated samples are consistent with those of the uncoated samples, while the (018)/(110) maintains distinct splitting, indicating that the coated samples still maintain a good layered structure of the ternary cathode material. No new diffraction peak appeared, indicating that no new phase was formed and no impurity phase was introduced.
(2) SEM images of the samples after composite coating of the polymer of example 1 and LFP were tested and the results are shown in fig. 2.
As can be seen from fig. 2: the coated sample keeps a good spherical structure, and the primary particles are full and round, which indicates that the coating does not affect the structure of the primary particles, and meanwhile, a plurality of white nanoparticles are distributed around the secondary particles, namely LFP nanoparticles. In addition, as can be seen from b in fig. 2, a relatively dense coating layer is formed on the surface of the secondary sphere, and the gaps between the primary particles are well filled. This may better block the contact of the electrolyte with the primary particles to cause side reactions, thereby contributing to improved cycle stability.
(3) The performance of the positive electrode materials prepared in the examples and comparative examples was tested, and the test results are shown in table 1. FIG. 3 is the first charge-discharge curve (blank discharge capacity 206.5mAh g) at 0.1C rate -1 、PAN 203.30 mAh g -1 Phenolic resin 202.05 mAh g -1 PEO assisted 201 mAh g -1 ). FIG. 4 shows 1 of samples obtained in examples and comparative examples00-circle cycle stability performance test result chart.
The test method comprises the following steps: mixing the obtained material with a conductive agent and a binder PVDF according to a ratio of 8.
TABLE 1 comparison of cell Performance of samples obtained in examples and comparative examples
Sample Polymer and method of making same 0.1C gram capacity (mAh g) -1 ） First coulombic efficiency (%) Capacity retention at 100 cycles at 1C (%) Charge transfer impedance Rct (omega)
Example 1 0.5wt% PAN LFP:NCM=1:9 20 2 .3 90.7 9 2 . 9 97
Example 2 1wt% PAN LFP:NCM=1:9 201.7 89.8 9 2 . 5 114
Example 3 0.2wt% PAN LFP:NCM=1:9 203.3 90.4 9 2 . 7 92
Example 4 2wt% PAN LFP:NCM=1:9 198.9 88.6 92.1 122
Example 5 LFP:NCM =1:7 191.39 89.8 93.86 1 39
Example 6 LFP:NCM =1:5 191.67 88.97 94.8 157
Example 7 LFP:NCM =1:3 189.40 89.53 94.33 175
Example 8 LFP:NCM =1:2 181.66 89.3 94.05 196.3
Comparative example 1 Blank Li Ni 0. 85 Co 0.1 Mn 0.05 O 2 20 6 . 5 90.9 87.2 57
Comparative example 2 0.5wt% phenolic resin 202.05 88.3 88.6 178
Comparative example 3 0.5wt%PEO 201.2 87.8 86.5 189
Comparative example 4 0.5wt% epoxy resin 199 85.9 80.2 212
Comparative example 5 Dry ball milling LFP/NCM (1 20 3 .3 9 1 . 2 9 0 . 7 147.5
Comparative example 6 5wt% PAN (excess PAN) 189.5 86.8 91.7 322
Comparative example 7 Non-addition-polymerized acrylonitrile 20 2 90.7 9 1 . 2 142.5
Comparative example 8 LFP:NCM=1:11 203 90.4 90.7 82
Comparative example 9 LFP: NCM =1:1 176 86.1 94.2 2 61
It can be seen by combining example 1 with comparative examples 1 to 4 and comparative example 7 that the addition of polyacrylonitrile is beneficial to significantly improve electrochemical performance and cycling stability, and if polyacrylonitrile is replaced by other raw materials, the product capacity exertion is reduced to different degrees, and impedance is significantly increased.
By comparing example 1 with comparative examples 5 to 6 and comparative examples 8 to 9: the usage amount of LFP and PAN needs to be strictly controlled, if the usage amount of PAN is too large, an interface layer between the ternary material and the lithium iron phosphate is thick, a charge transmission path is increased, the charge transfer impedance is obviously increased, and the specific capacity can be influenced; if the ratio of lithium iron phosphate to the NCM material is too high, a significant decrease in capacity and an increase in charge transfer resistance result.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. 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 (9)

1. The high-nickel ternary cathode material is characterized by comprising a ternary material body and a coating layer coated on the ternary material body, wherein the coating layer comprises polyacrylonitrile and lithium iron phosphate;
wherein the chemical formula of the ternary material body is LiNi x Co y Mn 1-x-y O 2 ；0.7＜x＜1.0，0.0＜y＜0.3；
The preparation process of the high-nickel ternary cathode material comprises the following steps: mixing and dissolving polyacrylonitrile and an organic solvent to obtain a first mixed solution, mixing the first mixed solution and the ternary material body to obtain a second mixed solution, and mixing the second mixed solution and lithium iron phosphate to obtain a mixed dispersion solution; treating the mixed dispersion liquid for 12-24 h at the temperature of 100-150 ℃.
2. The high-nickel ternary cathode material according to claim 1, wherein the mass ratio of the polyacrylonitrile to the ternary material body is 0.2-2.
3. A method for preparing the high-nickel ternary positive electrode material according to claim 1 or 2, comprising: mixing and dissolving polyacrylonitrile and an organic solvent to obtain a first mixed solution, mixing the first mixed solution and the ternary material body to obtain a second mixed solution, and mixing the second mixed solution and lithium iron phosphate to obtain a mixed dispersion solution; treating the mixed dispersion liquid for 12-24 h at the temperature of 100-150 ℃.
4. The preparation method of claim 3, wherein the polyacrylonitrile and the organic solvent are mixed and stirred for 2 to 10 hours to obtain the first mixed solution, and the concentration of the polyacrylonitrile in the first mixed solution is 1 to 8wt%.
5. The method according to claim 4, wherein the organic solvent is at least one selected from the group consisting of N, N-dimethylformamide, N-dimethylacetamide and azomethylpyrrolidone.
6. The method according to claim 4, wherein the molecular weight of the polyacrylonitrile is 100000-200000.
7. The preparation method according to claim 3, wherein in the preparation of the second mixed solution, the mass ratio of the polyacrylonitrile to the ternary material bulk is 0.2-2.
8. The preparation method according to claim 3, characterized by mixing the lithium iron phosphate with the second mixed solution, wherein the mass ratio of the lithium iron phosphate to the ternary material body is 1-9, and stirring for 1-6 h at 200-500 rpm;
the D50 of the lithium iron phosphate is 100-200 nm.
9. A lithium ion battery, characterized in that it is prepared by the high-nickel ternary cathode material according to any one of claims 1 or 2 or the high-nickel ternary cathode material prepared by the preparation method according to any one of claims 3 to 8.
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