CN114068899A

CN114068899A - Preparation method and application of self-assembled core-shell structure single crystal cathode material

Info

Publication number: CN114068899A
Application number: CN202111337329.3A
Authority: CN
Inventors: 徐士民; 吕菲; 李磊; 徐宁; 吴孟涛
Original assignee: Tianjin B&M Science and Technology Co Ltd
Current assignee: Tianjin B&M Science and Technology Co Ltd
Priority date: 2021-11-15
Filing date: 2021-11-15
Publication date: 2022-02-18

Abstract

The invention provides a preparation method and application of a self-assembled core-shell structure single crystal cathode material, which comprises the following steps: (1) preparing a two-dimensional layered structure metal carbon/nitride MXene material MX; (2) preparing a MX-loaded nickel-cobalt-manganese doped monocrystal precursor SP; (3) preparing a self-assembly double-layer film single crystal precursor B-SP modified on the surface of the SP; (4) preparing a precursor PP with a doped polycrystalline nickel-cobalt-manganese core-shell structure; (5) preparing a nickel-cobalt-manganese doped core-shell structure cathode material C; (6) preparing a precursor MOF-P of a single-layer film of a self-assembled metal-organic framework compound modified on the surface of the C; (7) preparing an oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC. The self-assembled core-shell structure single crystal cathode material can ensure the high temperature and the cycle performance of the single crystal material, further reduces the cracking of the crystal structure in the cycle process, improves the cycle and rate capability, and is suitable for large-scale production.

Description

Preparation method and application of self-assembled core-shell structure single crystal cathode material

Technical Field

The invention belongs to the field of nano materials, and particularly relates to a preparation method and application of a self-assembled core-shell structure single crystal anode material.

Background

MXene is a two-dimensional material with excellent performance reported in 2011 and has excellent metal conductivity;

self-assembly (Self-assembly) is a method of preparing long-range ordered crystal structures; the core-shell structure material can effectively improve the crystal structure stability of the material;

the lithium ion battery anode material is required to have high cycle and high rate characteristics, and the single crystal material has good high temperature and cycle performance. However, the art has not studied to prepare a positive electrode material using a single crystal material.

Disclosure of Invention

In view of the above, the present invention provides a preparation method and an application of a self-assembled core-shell structure single crystal positive electrode material, aiming at overcoming the defects in the prior art.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

the invention provides a preparation method of a self-assembled core-shell structure single crystal cathode material, which comprises the following steps:

(1) preparing a two-dimensional layered structure metal carbon/nitride MXene material MX:

adding metallic carbon/nitride MAX into a hydrofluoric acid solution, carrying out ultrasonic treatment, filtering and drying the solution after the reaction is finished, and obtaining a metallic carbon/nitride MXene material MX with a two-dimensional layered structure;

(2) preparing a MX-loaded nickel-cobalt-manganese doped monocrystal precursor SP:

adding the two-dimensional layered structure metal carbon/nitride MXene material MX obtained in the step (1) into an aqueous solution, adding nickel salt, cobalt salt, manganese salt and other metal salts into the aqueous solution, introducing protective gas, stirring, adjusting the pH value of the solution, filtering and drying the solution after reaction to obtain a MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP;

(3) preparing a single crystal precursor B-SP with a self-assembled double-layer film modified on the SP surface:

adding the MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP obtained in the step (2) into an aqueous solution, adding double-layer film molecules into the aqueous solution, stirring, adjusting the pH value of the solution, filtering, drying and sieving the solution after reaction to obtain a self-assembled double-layer film monocrystal precursor B-SP modified on the surface of the SP;

(4) preparing a precursor PP with a doped polycrystalline nickel-cobalt-manganese core-shell structure:

adding the SP surface modified self-assembled double-layer film single crystal precursor B-SP obtained in the step (3) and nickel salt, cobalt salt, manganese salt and other metal salts into an aqueous solution, introducing protective gas, stirring, adjusting the pH value of the solution, filtering and drying the solution after reaction to obtain a doped polycrystalline nickel-cobalt-manganese core-shell structure precursor PP;

(5) preparing a nickel-cobalt-manganese doped core-shell structure cathode material C:

uniformly mixing the doped polycrystalline nickel-cobalt-manganese core-shell structure precursor PP obtained in the step (4) with a lithium compound, calcining and cooling the mixture in the air or oxygen atmosphere, and preparing a nickel-cobalt-manganese core-shell structure doped positive electrode material C;

(6) preparing a precursor MOF-P of a single-layer film of a self-assembled metal-organic framework compound modified on the surface of C:

adding the nickel-cobalt-manganese doped core-shell structure cathode material C obtained in the step (5) into the mixed solution, adding a metal-organic framework compound into the mixed solution, stirring, adjusting the pH value of the solution, filtering, drying and sieving the solution after reaction to obtain a precursor MOF-P of a single-layer film of the metal-organic framework compound modified on the surface of the C;

(7) preparing an oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC:

and (3) adding the precursor MOF-P of the single-layer film of the self-assembled metal-organic framework compound modified on the surface of the cathode material C obtained in the step (6) into an aqueous solution, stirring, adjusting the pH value of the solution, filtering, drying and sieving the solution after reaction to obtain the oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC.

Further, the chemical general formula of the two-dimensional layered structure metal carbon/nitride MXene material MX in the step (1) is M_n+1X_nTx, wherein n is 1-3, M is at least one of titanium, zirconium, niobium, vanadium, molybdenum, strontium, chromium, tantalum or hafnium, X is at least one of carbon or nitrogen, and Tx is at least one of-OH, -O, -F or-Cl; the metal carbon/nitride MAX is a ternary layered compound, M atoms and A atomic layers are alternately arranged and closely stacked to form a hexagonal layered structure, and X atoms are filled in octahedral gaps; the mass percent concentration of the hydrofluoric acid solution is 5-40%; the temperature of the ultrasonic step is 20-80 ℃, and the ultrasonic frequency is 20-40 kHz; the reaction time is 5-100 hours; the two-dimensional layered structure metal carbon/nitride MXene material MX is two-dimensional layered metal carbon/nitride with nanoscale thickness.

Preferably, the mass percent concentration of the hydrofluoric acid solution is 20-30%; the temperature of the ultrasonic step is 25-50 ℃; the reaction time is 40-80 hours.

Further, the molar ratio of the two-dimensional layered structure metal carbon/nitride MXene material MX, nickel salt, cobalt salt and manganese salt to other metal salts in the step (2) is (0.0001-0.1): (0.1-1): (0.1-1): (0.1-1): (0-0.3); the nickel salt, the cobalt salt, the manganese salt and other metal salts are at least one of sulfate, nitrate, chloride or acetate; the other metal in the other metal salt is at least one of copper, silver, magnesium, aluminum, titanium, vanadium, zinc, germanium, molybdenum, indium, antimony, bismuth, barium, tungsten, palladium, strontium, cerium, niobium, zirconium, scandium or gallium; the protective atmosphere is at least one of nitrogen, helium or argon; the temperature of the stirring step is 10-90 ℃; the pH value is 7.0-12.0; the reaction time is 1-70 hours; the grain size of the MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP is 0.01-5 microns.

Preferably, the temperature of the stirring step is 45-80 ℃; the pH value is 9.0-11.5; the reaction time is 20-50 hours; the grain size of the MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP is 0.01-1 micron; the Tap Density (TD) of the MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP is as follows: TD is more than or equal to 3.0 and more than or equal to 0.3g/cm³(ii) a More preferably, 1.5. gtoreq.TD.gtoreq.0.3 g/cm³(ii) a Preferably, the specific surface area (Brunauer-Emmett-Teller method, BET) of the loaded MX-doped nickel-cobalt-manganese single crystal precursor SP is as follows: BET of more than or equal to 20.0 and more than or equal to 5.0m²(ii)/g; more preferably, 15.0. gtoreq.BET ≧ 9.0m²(ii)/g; the SP is a MX-loaded doped nickel-cobalt-manganese monocrystal precursor.

Further, the bilayer membrane molecule in the step (3) is at least one of polar amphipathic molecules; the polar amphiphilic molecule comprises a polar hydrophilic group and a hydrophobic group; the molar concentration of the polar amphiphilic molecules is 0.00001-1.0 mol/L; the temperature of the stirring step is 10-55 ℃; the pH value is 6.0-14.0; the grain diameter of the precursor B-SP of the SP surface modified self-assembled double-layer film single crystal is 0.015-15 microns; the thickness of the double-layer film molecule is 3-10 nanometers.

Preferably, the temperature of the stirring step is 20-45 ℃; the pH value is 7.0-10.0; the grain diameter of the precursor B-SP of the SP surface modified self-assembled double-layer film single crystal is 0.015-3 microns; the B-SP is a self-loading double-layer film single crystal precursor modified on the surface of the SP; the inner layer molecular polar group of the double-layer film molecule is adsorbed on the surface of the inner core single crystal precursor, the outer layer molecular polar group is distributed outwards, and the nonpolar group is arranged between the two layers of polar groups.

Further, the mol ratio of the precursor B-SP for modifying the self-assembly double-layer film on the SP surface in the step (4), nickel salt, cobalt salt, manganese salt and other metal salts is (0.001-1) (0.9-1): (0.2-1): (0.5-1): (0-0.3); the nickel salt, the cobalt salt, the manganese salt and other metal salts are at least one of sulfate, nitrate, chloride or acetate; the other metal in the other metal salt is at least one of copper, silver, magnesium, aluminum, titanium, vanadium, zinc, germanium, molybdenum, indium, antimony, bismuth, barium, tungsten, palladium, strontium, cerium, niobium, zirconium, scandium or gallium; the protective atmosphere is at least one of nitrogen, helium or argon; the temperature of the stirring step is 20-90 ℃; the pH value is 6.0-13.0; the reaction time is 1-100 hours; the grain diameter of the precursor PP with the doped polycrystalline nickel-cobalt-manganese core-shell structure is 1-50 microns.

Preferably, the temperature of the stirring step is 45-90 ℃; the pH value is 9.0-11.0; the reaction time is 10-60 hours; the PP is a precursor with a doped polycrystalline nickel-cobalt-manganese core-shell structure; the core of PP is MX doped nickel-cobalt-manganese monocrystal precursor, the shell of PP is doped polycrystalline nickel-cobalt-manganese, and the middle of the core-shell structure of PP is an amphiphilic molecule double-layer film.

Further, the mol ratio of the doped polycrystalline nickel-cobalt-manganese core-shell structure precursor PP in the step (5) to the lithium compound is 1: (1-3); the lithium compound is at least one of lithium hydroxide, lithium carbonate and lithium acetate; the temperature of the calcining step is 200-1000 ℃, and the temperature is kept for 1-100 hours; the particle size of the nickel-cobalt-manganese doped core-shell structure cathode material C is 1-70 microns; the core of the positive electrode material C with the nickel-cobalt-manganese doped core-shell structure is loaded MX doped nickel-cobalt-manganese single crystal, the shell is doped polycrystalline nickel-cobalt-manganese, and pyrolytic carbon layers, carbides and/or nitrides generated by pyrolysis are arranged between the core shells.

Preferably, the molar ratio of the doped polycrystalline nickel-cobalt-manganese core-shell structure precursor PP to the lithium compound in the step (5) is 1: (1-1.8); the temperature of the calcination step is 700-950 ℃; and C is a nickel-cobalt-manganese doped core-shell structure cathode material.

Further, the mixed solution in the step (6) is a mixed solution of a polar solvent and a non-polar solvent or one of the non-polar solvents; the polar solvent is at least one of water, alcohol compounds, ketone compounds, ether compounds, cyanogen compounds, amine compounds, lipid compounds, halogenated alkane or fatty acid compounds; the nonpolar solvent is at least one of saturated hydrocarbon compounds, benzene, petroleum ether, liquid paraffin, tetrachloromethane or dichloromethane; the metal in the metal-organic framework compound is at least one of titanium, aluminum, magnesium, molybdenum, vanadium, iron, nickel, cobalt or manganese; the pH value is 6.0-12.0; the temperature of the stirring step is 20-95 ℃; the reaction time is 1-100 hours; the drying step is vacuum drying, and the temperature is 30-150 ℃; the particle size of the precursor MOF-P of the single-layer film of the metal-organic framework compound modified on the surface of the C is 1-80 microns.

Preferably, the pH value is 7.0-10.0; the temperature of the stirring step is 45-85 ℃; the reaction time is 20-80 hours; the drying step is vacuum drying, and the temperature is 70-90 ℃; the MOF-P structure is C with a metal-organic framework compound adsorbed on the surface.

Further, the pH value in the step (7) is 6.0-14.0; the reaction time is 1-60 hours; the temperature of the stirring step is 10-400 ℃; the particle size of the oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC is 5-100 microns.

Preferably, the pH value in the step (7) is 9.0-12.0; the reaction time is 2-20 hours; the temperature of the stirring step is 120-300 ℃; the oxide-coated nickel-cobalt-manganese-doped core-shell-structured cathode material CC is of a four-layer spherical crystal structure and comprises four layers: the inner layer is a single crystal structure inner core, the outer layer of the inner layer is a carbonization layer with the thickness of 0.5-200 nanometers, the secondary outer layer is a spherical polycrystalline structure, and the outermost layer is an oxide and carbonization layer with the thickness of 1-200 nanometers.

More preferably, the outer surface of the inner layer is a carbonized layer with the thickness of 0.5-200 nanometers, which comprises a pyrolytic carbon layer, carbide and/or nitride generated by the pyrolysis of the amphiphilic molecule double-layer film; the outermost layer structure is a nano oxide film, the surface of the spherical crystal at the secondary outer layer is densely coated with the nano oxide film, and pyrolytic carbon is coated outside the nano oxide film; the pyrolytic carbon is derived from pyrolytic carbon generated by pyrolysis of hydrophobic groups of assembled metal-organic framework compound monomolecular layers.

The invention provides a self-assembled core-shell structure single crystal anode material which is prepared by the method.

The invention provides an application of a self-assembled core-shell structure single crystal cathode material, and the application of the cathode material in the preparation of a lithium ion secondary battery.

Compared with the prior art, the invention has the following advantages:

the self-assembled core-shell structure single crystal positive electrode material adopts MXene two-dimensional material with excellent conductivity to prepare a single crystal core nickel-cobalt-manganese ternary precursor, controls the particle size, tap density and specific surface area of the single crystal core nickel-cobalt-manganese ternary precursor, and adsorbs a bimolecular film on the surface of the single crystal precursor through molecular self-assembly; through electrostatic attraction, hydroxide ions generated by ionization of nickel, cobalt, manganese and other metal ions and ammonia water on the outer layer of the double-molecular membrane are electrostatically attracted on the surface of the double-layer membrane through polar charged functional groups, and nucleation and crystallization are performed on the surface of the double-layer membrane to generate a polycrystalline nickel-cobalt-manganese shell crystal structure; and then, carrying out molecular self-assembly of a single-layer film by a metal-organic framework compound, and carrying out hydrolysis and sintering reaction to generate the oxide-coated nickel-cobalt-manganese doped core-shell structure anode material with a single crystal shell of a polycrystalline structure.

The self-assembled core-shell structure single crystal cathode material can ensure the high temperature and the cycle performance of the single crystal material, further reduces the cracking of the crystal structure in the cycle process, improves the cycle and rate capability, and is suitable for large-scale production.

Drawings

FIG. 1 is a schematic illustration of the product of a reaction process;

FIG. 2 is an SEM image of MX prepared in step (1) of example 1;

FIG. 3 is a particle size distribution diagram of SP prepared in step (2) of example 1;

FIG. 4 is an SEM image of SP prepared in step (2) of example 1;

FIG. 5 is a particle size distribution diagram of B-SP prepared in step (3) of example 1;

FIG. 6 is an SEM image of B-SP prepared in step (3) of example 1;

FIG. 7 is a particle size distribution diagram of PP prepared in step (4) of example 1;

FIG. 8 is an SEM image of PP prepared in step (4) of example 1;

FIG. 9 is an SEM image of C prepared in step (5) of example 1;

FIG. 10 is an SEM image of MOF-P prepared in step (6) of example 1;

FIG. 11 is an SEM image of a CC prepared in step (7) of example 1;

FIG. 12 is a graph showing the charge/discharge high-temperature cycle capacity retention rates at 45 ℃ of 1/3C in the thin film batteries of example 1 and comparative example 1;

FIG. 13 is a graph showing the charge/discharge high-temperature cycle capacity retention rate at 45 ℃ of 1/3 ℃ in example 1 and comparative example 2;

FIG. 14 is an SEM image of MX prepared in step (1) of example 2;

FIG. 15 is an SEM image of SP prepared in step (2) of example 4;

FIG. 16 is a graph showing the charge and discharge high-temperature cycle capacity retention rates at 45 ℃ of 1/3C in the thin film batteries of example 4 and comparative example 3;

FIG. 17 is a graph showing the charge and discharge high-temperature cycle capacity retention rates at 45 ℃ of 1/3C in the thin film batteries of example 6, example 1 and comparative example 1;

figure 18 is the XRD spectrum of example 7;

FIG. 19 is a graph showing the cycle capacity retention rate at 45 ℃ and 1/3 ℃ for high temperature charge and discharge in thin film batteries of example 7, example 1 and comparative example 1.

Detailed Description

Unless defined otherwise, technical terms used in the following examples have the same meanings as commonly understood by one of ordinary skill in the art to which the present invention belongs. The test reagents used in the following examples, unless otherwise specified, are all conventional biochemical reagents; the experimental methods are conventional methods unless otherwise specified.

And (3) material performance characterization:

1) the surface morphology of the material was carried out on a JSM-6510 scanning electron microscope, JEOL, Japan, and an EV018 scanning electron microscope, Zeiss, Germany, and the X-ray energy scattering EDS spectra and the elemental surface distribution maps were carried out on an Oxford X-MAX 20 energy spectrometer.

2) The median particle size of the material particles was carried out on a malvern Mastersizer 2000 laser particle sizer in the uk.

3) The mass percentage content of the element nickel is measured by a gravimetric method; the mass percentage content of the element cobalt is measured by adopting a potentiometric titration method; the mass percentage content of the element manganese is determined by a titration method; measuring the mass percentage of the element fluorine by adopting an ion selective electrode method; the content of other metal elements is measured by ICP method.

4) The crystal structure test is carried out on a D/max 2500VL/PC type XRD diffractometer of Japan science company, a copper target is adopted, the test precision is +/-0.02 degrees, and the scanning range is from 5 degrees to 90 degrees.

5) The specific surface area of the material is carried out on a Bechard BSD-660 full-automatic high-performance physical adsorption instrument.

And (3) electrochemical performance testing:

1) electricity withholding test

According to the mass ratio of 90: 2: 8, weighing an anode active material (the anode active material is amorphous powder formed after the silicon-titanium alloy prepared in the example 1 is ball-milled for 120 hours, and the carbon-coated silicon-titanium nitride alloy cathode material generated in the example 2), a conductive agent Super P and a binder PVDF (HSV900), adding a proper amount of N-methylpyrrolidone as a solvent, and stirring for 15 hours by using a magnetic stirrer in a glove box under the protection of argon to prepare slurry required for power-on. The coating machine is an MSK-AFA-III automatic coating dryer of Shenzhen Kejing Zhi Daji science and technology Limited, the coating gap is 25 micrometers, the speed is 5 centimeters/minute, the slurry is uniformly coated on a 9-micrometer-thick polished copper foil with the purity of 99.8 percent produced by Meixian Jinxiang copper foil Limited, the vacuum drying is carried out for 12 hours at the temperature of 120 ℃, and then an electrode slice with the diameter of about 16 millimeters is punched by a Shenzhen Kejing MSK-T06 button cell punching machine. CR2032 coin cells were assembled in a german blaun glove box filled with 99.9% high purity argon. A Shenzhenjian crystal MSK-110 small-sized hydraulic button battery packaging machine is adopted. The cathode is a high-purity lithium sheet with the purity of 99.99 percent and the diameter of 15.8 millimeters, the diaphragm is a American ENTEK LP16 type PE diaphragm with the thickness of 16 micrometers, and the electrolyte is DMC: EMC (60:40, mass ratio), VC (2% of the total mass of DMC and EMC) and 1.3mol/L LiPF6 were added. Button cell cycling and rate testing was performed on a CT2001A tester by wuhan blue electronics ltd.

2) Thin film battery testing

The mass ratio of the positive electrode material is as follows: conductive agent: binder (97.8:1.2: 2); the negative electrode is prepared from graphite G49: conductive agent: the adhesive (96:2:2) was used, and the test voltage was 3.0-4.25V.

The oxide-coated nickel-cobalt-manganese-doped core-shell-structure cathode material prepared by the preparation method can ensure the high-temperature and cycle performance of the single crystal material, further reduce the cracking of the crystal structure in the cycle process, improve the cycle and rate capability, and is suitable for large-scale production.

and (3) adding the precursor MOF-P of the single-layer film of the self-assembled metal-organic framework compound modified on the surface of the cathode material C obtained in the step (6) into an aqueous solution, stirring, adjusting the pH value of the solution, filtering, drying and sieving the solution after reaction to obtain the oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC. FIG. 1 is a schematic representation of the product of the reaction process.

The present invention will be described in detail with reference to examples.

Example 1

A preparation method of a self-assembled core-shell structure single crystal cathode material comprises the following steps:

weigh 20g of Ti₃AlC₂Adding 60mL of 10% HF acid solution into ceramic powder, stirring at the constant temperature of 35 ℃ for 50 hours, after the reaction is finished, performing centrifugal separation, cleaning the product with deionized water for 3 times until the pH value is 7.0, drying in a vacuum oven at 100 ℃ for 10 hours to prepare MX product Ti₃C₂MXene black two-dimensional layered metal carbide, fig. 2 is an SEM image of MX;

dissolving 0.35g of MX obtained in the step (1) in 1L of ultrapure water, performing ultrasonic dispersion, and mixing nickel sulfate, cobalt sulfate, manganese sulfate and aluminum sulfate according to a molar ratio of 62: 5: 13: 0.05 preparing a mixed salt solution (1.2mol/L), adding an MX aqueous solution into the mixed solution, uniformly stirring and mixing, co-currently pumping the mixed solution, 3mol/L NaOH solution and ammonia water solution (10.5 wt%) into a reaction kettle, filling nitrogen into the reaction kettle, controlling the temperature in the reaction kettle to be 40 ℃, controlling the pH value in the reaction kettle to be 10.0-12.0, starting a stirring device in the reaction kettle, controlling the stirring speed of the stirring device to be 1200rpm/min, reacting for 5 hours, aging a reaction product obtained by the reaction for 0.5 hour, performing filter pressing washing, and drying at 100 ℃ under air conditions to prepare a MX-doped manganese single crystal precursor SP with the D50 of 3.05 mu m, wherein the particle size distribution diagram and the SEM diagram of the SP are shown in figures 3-4, and the element content of the SP is shown in Table 1:

TABLE 1 elemental content analysis of SP

Item	Measured value	Measuring methods or apparatus
			Ni(mol％)	61.79	Gravimetric method
Co(mol％)	4.98	Potentiometric titration
			Mn(mol％)	12.86	Titration method
Al(wt％)	0.43	ICP

adding 1L of 0.01mol/L dimyristoyl phosphatidylcholine (DMPC) into 100g of MX-loaded doped nickel-cobalt-manganese single crystal precursor SP obtained in the step (2), uniformly stirring, adjusting the pH value of the solution to 7.0 and the constant temperature to 25 ℃, filtering the solution after 1 hour, drying at the temperature of 80 ℃, and sieving by a 300-mesh sieve to obtain a product D50 which is 3.09 mu m B-SP, wherein B-SP is a self-assembled bilayer membrane single crystal precursor modified on the surface of SP, dimyristoyl phosphatidylcholine polar groups are electrostatically adsorbed on the surface of SP to form a self-assembled bilayer membrane, and the particle size distribution diagram and the SEM diagram of B-SP are shown in FIGS. 5-6;

mixing 100g B-SP obtained in the step (3) and nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate according to a molar ratio of 80: 3: 17: 0.03 of mixed salt solution (3.0mol/L) is stirred and mixed uniformly in a high-purity nitrogen atmosphere, B-SP is used as nucleation seed crystal, the mixed solution, NaOH solution (3mol/L) and ammonia water solution (15 wt%) are pumped into a reaction kettle in a concurrent flow mode, the reaction kettle is filled with nitrogen, the temperature in the reaction kettle is controlled to be 55 ℃, the pH value in the reaction kettle is controlled to be 10.5-12.5, the stirring speed is 1000rpm/min, the reaction is carried out for 24 hours, a reaction product obtained by the reaction is aged, filter-pressed and washed, and dried at 100 ℃ under the air condition, a product PP with the D50 of 10.30 mu m is obtained, the product PP is a doped polycrystalline nickel-cobalt-manganese structure precursor, and the PP core is an MX doped nickel-cobalt-manganese single crystal precursor prepared in the core-shell step (2); the middle of the PP core-shell structure is an amphiphilic molecule DMPC double-layer membrane prepared in the step (3); the PP shell prepared in the step (4) is doped with polycrystalline nickel, cobalt and manganese, the particle size distribution diagram and the SEM image of the PP are shown in figures 7-8, and the element content analysis of the PP is shown in Table 2:

TABLE 2 elemental content analysis of PP

Item	Measured value	Measuring methods or apparatus
			Ni(mol％)	79.83	Gravimetric method
Co(mol％)	2.97	Potentiometric titration
			Mn(mol％)	16.45	Titration method
Al(wt％)	0.28	ICP

uniformly mixing PP obtained in the step (4) and lithium hydroxide monohydrate according to a molar ratio of 1:1.10, sintering in a muffle furnace under an oxygen atmosphere at a temperature of 3 ℃/min and 25 ℃ to 400 ℃, preserving heat for 10 hours at 5 ℃/min, raising the temperature of 400 ℃ to 900 ℃, preserving heat for 12 hours, cooling to room temperature, jaw breaking, grinding and sieving with a 400-mesh sieve to obtain a D5013.27 mu m product C, wherein the C is a doped nickel-cobalt-manganese core-shell structure anode material, the core is a loaded MX doped nickel-cobalt-manganese single crystal generated by sintering at 400 ℃ in an oxygen atmosphere, the shell is doped polycrystalline nickel-cobalt-manganese generated by sintering at 900 ℃ in an oxygen atmosphere, a pyrolytic carbon layer, a carbide and a nitride generated by pyrolyzing a DMPC double-layer film are arranged between core shells, and the SEM image of the C is shown in figure 9;

mixing and stirring 100g C and 2L ethanol obtained in the step (5) with petroleum ether (according to a volume ratio of 80:20), adding 5mL tetrabutyl titanate into the mixed solution, stirring uniformly, keeping the temperature at 25 ℃, filtering the solution after 5 hours of reaction time, drying at 90 ℃ in vacuum, and sieving with a 400-mesh sieve to obtain a D5013.70 mu m product MOF-P, wherein the MOF-P is a precursor of a self-assembled monolayer film of tetrabutyl titanate modified on the surface of C, and the SEM image of the MOF-P is shown in figure 10.

and (3) dissolving 100g of MOF-P obtained in the step (6) in an aqueous solution, adjusting the pH value of the solution to be 6.5, keeping the temperature at 25 ℃, filtering the solution after 1 hour of reaction time, drying the solution in the air at 100 ℃, and sieving the dried solution through a 400-mesh sieve to obtain a product CC with the diameter of D5014.57 microns, wherein the CC is a titanium dioxide and pyrolytic carbon coated nickel-cobalt-manganese doped core-shell structure cathode material. The structure of the product CC is a four-layer spherical crystal structure; comprises four layers: the core is a loaded MX doped nickel cobalt manganese single crystal generated by sintering at 400 ℃ in an oxygen atmosphere, the shell is doped polycrystalline nickel cobalt manganese generated by sintering at 900 ℃ in an oxygen atmosphere, a pyrolytic carbon layer, carbide and nitride generated by pyrolysis of a DMPC double-layer film, titanium dioxide and a pyrolytic carbon coating layer are arranged between the core shells, and an SEM image of a CC is shown in figure 11.

Example 2

The difference from the embodiment 1 is that: in step (1), 20g of Ti was weighed₃AlC₂Adding 100mL of 20% HF acid solution into ceramic powder, stirring at the constant temperature of 25 ℃ for 100 hours, after the reaction is finished, centrifugally separating, washing the product with deionized water for 3 times until the pH value is 7.0, and drying in a vacuum oven at 70 ℃ for 15 hours. Preparing MX product Ti₃C₂MXene black two-dimensional layered metal carbide.

The SEM image of MX prepared is shown in fig. 14, and the cycle capacity retention rates of thin film batteries tested in example 1 and example 2 are substantially the same.

Example 3

The difference from the embodiment 1 is that: and (3) adding 1L of 0.01 mol/L1-palmitoyl-2-oleoyl lecithin (POPC) and 1L of 0.01mol/L dicaprylyl lecithin (DEPC) into 100g of MX-loaded doped nickel-cobalt-manganese single crystal precursor SP.

Thin film battery test examples 1 and 3 had substantially the same cycle capacity retention.

The bilayer in the step (3) can be suitable for two molecules containing more than two kinds of multiple bilayer membranes;

and (3) the nano carbonized layer generated by pyrolysis has the capacity cycle attenuation function of relieving the material deformation caused by the volume change of the oxide-coated nickel-cobalt-manganese-doped core-shell structure cathode material in the circulation process.

Example 4

The difference from the embodiment 1 is that: in the step (2), nickel sulfate, cobalt sulfate, manganese sulfate and copper nitrate are mixed according to a molar ratio of 75: 3: 22: 0.07 mixed salt solution (1.5mol/L) is prepared to obtain the MX-loaded doped nickel-cobalt-manganese single crystal precursor SP with the D50 of 3.11 mu m.

The SEM photograph of the SP prepared in step (2) is shown in FIG. 15.

Example 5

The difference from the embodiment 1 is that: and (5) uniformly mixing the PP obtained in the step (4) and lithium hydroxide monohydrate in a molar ratio of 1:1.05 to obtain a D5013.74 mu m product C.

Thin film battery test example 1 and example 5 have substantially the same cycle capacity retention.

Example 6

The difference from the embodiment 1 is that: and (6) mixing and stirring 100g C and 3L of ethanol and cyclohexane (in a volume ratio of 70:30) obtained in the step (5), adding 5g of triethylaluminum into the mixed solution, uniformly stirring, keeping the temperature at 35 ℃, filtering the solution after 10 hours of reaction time, drying at 90 ℃ in vacuum, and sieving with a 400-mesh sieve to obtain a D5013.57 mu m product MOF-P, wherein the MOF-P is a precursor of a self-contained monolayer film of triethylaluminum modified on the surface of C.

The charge and discharge high temperature cycle capacity retention rates of the thin film batteries of example 6, example 1 and comparative example 1 at 45 ℃ 1/3C are shown in FIG. 17.

The thin film battery tests the cycle capacity retention rate of the example 1, the comparative example 1 and the example 6, the example 1 and the example 6 are basically the same, and the cycle capacity retention rate of the example 1 and the example 6 is better than that of the comparative example 1.

Example 7

The difference from the embodiment 1 is that: in the step (2), nickel sulfate, cobalt sulfate, manganese sulfate and copper nitrate are mixed according to a molar ratio of 75: 3: 22: 0.07 preparing mixed salt solution (1.5mol/L) to obtain a load MX doped nickel-cobalt-manganese single crystal precursor SP with D50 of 3.11 mu m;

step (4) mixing 100g B-SP prepared in step (3) and nickel sulfate, cobalt sulfate, manganese sulfate and aluminum nitrate according to a molar ratio of 90: 2: 8: stirring and uniformly mixing 0.05 mixed salt solution (3.0mol/L) in a high-purity nitrogen atmosphere, and obtaining a product PP with the D50 of 13.27 mu m by the same preparation conditions as the step (4), wherein the product PP is a precursor of a doped polycrystalline nickel-cobalt-manganese core-shell structure; taking a PP core as the MX doped nickel-cobalt-manganese monocrystal precursor prepared in the step (2); the middle of the PP core-shell structure is an amphiphilic molecule DMPC double-layer membrane prepared in the step (3); the PP shell is prepared by doping polycrystalline nickel, cobalt and manganese in the step (4);

mixing and stirring 100g C obtained in the step (5), 3L of ethanol and benzene (in a volume ratio of 750:25), adding 2g of tetrabutyl titanate, 2g of triethyl aluminum and 2g of aluminum isopropoxide into the mixed solution, uniformly stirring, keeping the temperature at 25 ℃, filtering the solution after 10 hours of reaction time, drying at 90 ℃ in vacuum, and sieving with a 400-mesh sieve to obtain a D5015.68 mu m product MOF-P, wherein the MOF-P is a precursor of the self-contained monolayer film of triethyl aluminum modified on the surface of C;

the XRD spectrum of example 7 is shown in fig. 18;

the graphs of the capacity retention rates of the thin film batteries of example 7, example 1 and comparative example 1 at 45 ℃ and 1/3 ℃ during high-temperature charging and discharging cycles are shown in FIG. 19.

The thin film battery tests the cycle capacity retention of example 1, comparative example 1 and example 7, the cycle capacity retention of example 7 is slightly better than that of example 1, and the cycle capacity retention of example 1 and example 7 is better than that of comparative example 1.

Comparative example 1

The difference from the embodiment 1 is that: the process of step (3) is not included.

The gram-capacity, first-time efficiency and average voltage of the thin film batteries 01C/0.1C of example 1 and comparative example 1 are shown in table 3.

TABLE 3 comparison table of 01C/0.1C formation gram capacity, first efficiency and average voltage of thin film battery

Example 1 has a slightly lower gram capacity, slightly lower first efficiency than comparative example 1, and example 1 has a slightly higher average voltage than comparative example 1.

The capacity retention rates of the thin film batteries of the example 1 and the comparative example 1 at 45 ℃ and 1/3C in the high-temperature charging and discharging cycle are shown in FIG. 12, and the capacity retention rate of the example 1 is higher than that of the comparative example 1.

The nano carbonized layer generated by pyrolysis in the step (3) has the capacity cycle attenuation function of relieving the material deformation caused by the volume change of the oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material in the circulation process.

Comparative example 2

The difference from the embodiment 1 is that: and (4) adding 1L of 0.01 mol/L1-palmitoyl-2-oleoyl lecithin (POPC) into 100g of MX-loaded doped nickel-cobalt-manganese single crystal precursor SP obtained in the step (3).

The capacity retention rates of the example 1 and the comparative example 2 at the temperature of 45 ℃ and the temperature of 1/3 ℃ during the charge and discharge high-temperature cycle are shown in FIG. 13, and the capacity retention rate of the example 1 is substantially consistent with that of the comparative example 2.

The bilayer in the step (3) is applicable to a wide range of bilayer membrane molecules;

Comparative example 3

The difference from the example 4 lies in: the process of step (3) is not included.

The capacity retention rates of the thin film batteries of example 4 and comparative example 3 at 45 ℃ and 1/3C during high-temperature charging and discharging cycles are shown in FIG. 16, and the capacity retention rate of example 4 is higher than that of comparative example 3.

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

1. A preparation method of a self-assembled core-shell structure single crystal cathode material is characterized by comprising the following steps: the method comprises the following steps:

2. Ad hoc as claimed in claim 1The preparation method of the core-shell structure single crystal anode material is characterized by comprising the following steps of: the chemical general formula of the two-dimensional layered structure metal carbon/nitride MXene material MX in the step (1) is M_n+1X_nTx, wherein n is 1-3, M is at least one of titanium, zirconium, niobium, vanadium, molybdenum, strontium, chromium, tantalum or hafnium, X is at least one of carbon or nitrogen, and Tx is at least one of-OH, -O, -F or-Cl; the metal carbon/nitride MAX is a ternary layered compound, M atoms and A atomic layers are alternately arranged and closely stacked to form a hexagonal layered structure, and X atoms are filled in octahedral gaps; the mass percent concentration of the hydrofluoric acid solution is 5-40%; the temperature of the ultrasonic step is 20-80 ℃, and the ultrasonic frequency is 20-40 kHz; the reaction time is 5-100 hours; the two-dimensional layered structure metal carbon/nitride MXene material MX is two-dimensional layered metal carbon/nitride with nanoscale thickness.

3. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the molar ratio of the two-dimensional layered structure metal carbon/nitride MXene material MX, nickel salt, cobalt salt and manganese salt to other metal salts in the step (2) is (0.0001-0.1): (0.1-1): (0.1-1): (0.1-1): (0-0.3); the nickel salt, the cobalt salt, the manganese salt and other metal salts are at least one of sulfate, nitrate, chloride or acetate; the other metal in the other metal salt is at least one of copper, silver, magnesium, aluminum, titanium, vanadium, zinc, germanium, molybdenum, indium, antimony, bismuth, barium, tungsten, palladium, strontium, cerium, niobium, zirconium, scandium or gallium; the protective atmosphere is at least one of nitrogen, helium or argon; the temperature of the stirring step is 10-90 ℃; the pH value is 7.0-12.0; the reaction time is 1-70 hours; the grain size of the MX-loaded doped nickel-cobalt-manganese monocrystal precursor SP is 0.01-5 microns.

4. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the double-layer membrane molecules in the step (3) are at least one of polar amphiphilic molecules; the polar amphiphilic molecule comprises a polar hydrophilic group and a hydrophobic group; the molar concentration of the polar amphiphilic molecules is 0.00001-1.0 mol/L; the temperature of the stirring step is 10-55 ℃; the pH value is 6.0-14.0; the grain diameter of the precursor B-SP of the SP surface modified self-assembled double-layer film single crystal is 0.015-15 microns; the thickness of the double-layer film molecule is 3-10 nanometers.

5. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the mol ratio of the SP surface modified self-assembly double-layer film single crystal precursor B-SP, the nickel salt, the cobalt salt and the manganese salt to other metal salts in the step (4) is (0.001-1) (0.9-1): (0.2-1): (0.5-1): (0-0.3); the nickel salt, the cobalt salt, the manganese salt and other metal salts are at least one of sulfate, nitrate, chloride or acetate; the other metal in the other metal salt is at least one of copper, silver, magnesium, aluminum, titanium, vanadium, zinc, germanium, molybdenum, indium, antimony, bismuth, barium, tungsten, palladium, strontium, cerium, niobium, zirconium, scandium or gallium; the protective atmosphere is at least one of nitrogen, helium or argon; the temperature of the stirring step is 20-90 ℃; the pH value is 6.0-13.0; the reaction time is 1-100 hours; the grain diameter of the precursor PP with the doped polycrystalline nickel-cobalt-manganese core-shell structure is 1-50 microns.

6. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the mol ratio of the doped polycrystalline nickel-cobalt-manganese core-shell structure precursor PP in the step (5) to the lithium compound is 1: (1-3); the lithium compound is at least one of lithium hydroxide, lithium carbonate and lithium acetate; the temperature of the calcining step is 200-1000 ℃, and the temperature is kept for 1-100 hours; the particle size of the nickel-cobalt-manganese doped core-shell structure cathode material C is 1-70 microns; the core of the positive electrode material C with the nickel-cobalt-manganese doped core-shell structure is loaded MX doped nickel-cobalt-manganese single crystal, the shell is doped polycrystalline nickel-cobalt-manganese, and pyrolytic carbon layers, carbides and/or nitrides generated by pyrolysis are arranged between the core shells.

7. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the mixed solution in the step (6) is a mixed solution of a polar solvent and a non-polar solvent or one of the non-polar solvents; the polar solvent is at least one of water, alcohol compounds, ketone compounds, ether compounds, cyanogen compounds, amine compounds, lipid compounds, halogenated alkane or fatty acid compounds; the nonpolar solvent is at least one of saturated hydrocarbon compounds, benzene, petroleum ether, liquid paraffin, tetrachloromethane or dichloromethane; the metal in the metal-organic framework compound is at least one of titanium, aluminum, magnesium, molybdenum, vanadium, iron, nickel, cobalt or manganese; the pH value is 6.0-12.0; the temperature of the stirring step is 20-95 ℃; the reaction time is 1-100 hours; the drying step is vacuum drying, and the temperature is 30-150 ℃; the particle size of the precursor MOF-P of the single-layer film of the metal-organic framework compound modified on the surface of the C is 1-80 microns.

8. The preparation method of the self-assembled core-shell structure single crystal cathode material according to claim 1, characterized in that: the pH value in the step (7) is 6.0-14.0; the reaction time is 1-60 hours; the temperature of the stirring step is 10-400 ℃; the particle size of the oxide-coated nickel-cobalt-manganese doped core-shell structure cathode material CC is 5-100 microns.

9. A self-assembled core-shell structure single crystal cathode material is characterized in that: the positive electrode material is produced by the method according to any one of claims 1 to 8.

10. The application of the self-assembled core-shell structure single crystal cathode material of claim 9 is characterized in that: the application of the cathode material in the preparation of lithium ion secondary batteries.