CN109301207B - Surface layer doped with Ce3+And the surface layer is coated with CeO2NCM ternary cathode material and preparation method thereof - Google Patents

Surface layer doped with Ce3+And the surface layer is coated with CeO2NCM ternary cathode material and preparation method thereof Download PDF

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CN109301207B
CN109301207B CN201811127786.8A CN201811127786A CN109301207B CN 109301207 B CN109301207 B CN 109301207B CN 201811127786 A CN201811127786 A CN 201811127786A CN 109301207 B CN109301207 B CN 109301207B
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surface layer
ncm
ceo
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cathode material
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CN109301207A (en
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陈来
李晴
苏岳锋
吴锋
卢赟
包丽颖
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Beijing Institute of Technology BIT
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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
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    • H01M4/362—Composites
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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
    • 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
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/485—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of mixed oxides or hydroxides for inserting or intercalating light metals, e.g. LiTi2O4 or LiTi2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
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    • 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
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    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to a surface layer doped with Ce3+And the surface layer is coated with CeO2Belonging to the field of chemical energy storage batteries. The chemical formula of the material is wCeO2‑Li[Ni1‑x‑y‑zMnxCoyCez]O2Wherein 0.8<1‑x‑y‑z<1，0<x+y+z<0.2, w + z is more than or equal to 0.005 and less than or equal to 0.03; the method comprises the steps of ultrasonically processing cerium nitrate and an NCM ternary positive electrode material in ethanol for 1-2 hours, then uniformly grinding, calcining at 500-750 ℃ for 4-6 hours, and cooling along with a furnace to obtain the cerium nitrate ternary positive electrode material. Ce3+Stabilizes the layered frame structure of the NCM ternary cathode material and reduces Li in the surface layer of the cathode material+/Ni2+Mixed arrangement of (1); surface layer CeO2The coating stabilizes the electrolyte/electrode interface structure; the rate capability and the cycle stability of the NCM ternary cathode material are obviously improved.

Description

Surface layer doped with Ce3+And the surface layer is coated with CeO2NCM ternary cathode material and preparation method thereof
Technical Field
The invention relates to surface layer dopingCe3+And the surface layer is coated with CeO2Belonging to the field of chemical energy storage batteries.
Background
At present, fossil energy such as coal, petroleum, natural gas and the like is increasingly exhausted, and in addition, the problem of environmental pollution gradually becomes a key problem concerned by various countries. The development of pure electric vehicles and oil-gas hybrid vehicles is more and more concerned by people. There is a need for rapid development of lithium secondary batteries to meet the urgent need for practical application of new energy batteries. In the family of lithium secondary batteries, lithium cobaltate, lithium iron phosphate and ternary materials in turn play an important role in the market. Lithium cobaltate is mostly applied to small portable electronic equipment, and lithium iron phosphate is gradually replaced by ternary materials to play a role in the aspect of power electric automobiles due to low specific mass capacity. The release of Tesla followed 2012 by NCA (Li [ Ni ]0.85Co0.1Al0.05]O2) After the ternary positive electrode material is used as an electric vehicle Model S of a power battery, the wave of the ternary positive electrode material is continuously increased through research in various parts of the world. China also develops high-voltage and high-nickel anode ternary materials without any residual force so as to meet the requirements of a new generation of high-capacity electrode materials.
NCM(Li[NixCoyMn1-x-y]O2，x>0.5) the ternary cathode material has higher specific discharge capacity>200mAh/g) is the most potential positive battery material. However, at present, the NCM ternary cathode material has not been widely used commercially, and one of the main reasons is that the cycle stability and rate capability of the NCM ternary cathode material are poor. This is because Ni element is segregated and enriched on the surface during the synthesis of the NCM ternary positive electrode material, and Li element+And Ni2+Have similar ionic radii, Li is likely to occur during electrochemical charge-discharge cycling+/Ni2+Mixed and arranged to change the structure of the NCM ternary cathode material, thereby affecting the electrochemical stability and electrochemical cycle performance of the NCM ternary cathode material (Nickel-Rich and Lithium-Rich Layered Oxide catalysts: Progress and Perspectives, Arumugam Manthiiram, James C.Knight, Seung-Taek Yung, Seung-Min Oh,and Yang-Kook Su,Adv.Energy Mater.2016,6,1501010)。
Because Ni ions are easily oxidized into Ni in the delithiated state4+Ionic, and Ni of surface layer of NCM ternary positive electrode material4 +Is extremely unstable; meanwhile, the electrolyte is easy to be subjected to oxidative decomposition under high pressure, decomposition products are deposited on the surface of the NCM ternary cathode material, and acidic substances in the electrolyte are likely to further corrode the surface layer of the NCM ternary cathode material. For these reasons, the surface layer of the NCM ternary positive electrode material undergoes a transition from a layered structure to a spinel structure. Therefore, the stable interface structure is important for improving the electrochemical performance of the high-nickel cathode material. In addition, it is widely believed that the phase transition process of the NCM ternary cathode material gradually diffuses from the surface layer to the inside, so it is important to enhance the stability of the surface layer of the NCM ternary cathode material. Through research, Ce4+The ions have strong oxidizing property, and the surface layer can enter Ni of the Li layer after being doped into crystal lattices2+Oxidation of ions to Ni3+Ion, and returning it to the 3b position of the transition metal layer (Ce-doped LiNi)1/3Co(1/3-x/3)Mn1/3Cex/3O2The decrease in Li, i.e., decrease in Li, such as the amount of catalyst materials for use in lithium ion batteries, Zhang Yingjie, Xia Shubaiao, Zhang Yannan, Dong Peng, Yan Yuxing, Yang Ruiming, Chinese Science Bulletin,2012,57(32),4181-+/Ni2+And (4) mixing and discharging. And CeO2Can be used as a fast ion conductor (the nanometer CeO is synthesized by a precipitation method2And properties thereof, Song Xiaolan, Qiu guanzhou, Qupeng, Yangxuan, Wu Xuelan, Wang Haibo, university of Hunan's bulletin (Nature science edition), 2004, 31(6), 13-17), by adjusting the calcination temperature, the coating was made on the surface of the positive electrode material. But only Ce3+Doped with or of CeO2The coated NCM ternary cathode material still has the problems of poor cycle stability and serious attenuation of capacity and structure along with the electrochemical process.
Disclosure of Invention
In view of the above, the present invention is directed to a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material and the preparation method thereof are provided byDoping with Ce3+Entering the surface crystal lattice to stabilize the layered frame structure in the circulating process. The doping origin ion being Ce4+，Ce4+Ni with strong oxidizing power capable of leading surface layer to enter Li layer 3a position2+Oxidation to Ni3+So as to return to the position of the transition metal layer 3b, thus reducing Li+/Ni2+Mixing and discharging Li+The embedding and detaching process is more convenient and faster. At the same time Ce4+Is reduced to Ce3+And the metal layer exists in the positive electrode transition metal layer to stabilize the frame structure. And the surface layer of CeO2The coating can isolate the direct contact between the electrolyte and the electrode, stabilize the interface structure of the electrolyte/electrode and slow down the continuous increase of surface charge transfer resistance and surface polarization in the circulation process.
The purpose of the invention is realized by the following technical scheme.
Surface layer doped with Ce3+And the surface layer is coated with CeO2The chemical formula of the NCM ternary cathode material is wCeO2-Li[Ni1-x-y-zMnxCoyCez]O2Wherein x is>0，y>0，z>0，w>0，0.8<1-x-y-z<1， 0<x+y+z<0.2，0.005≤w+z≤0.03。
Surface layer doped with Ce3+And the surface layer is coated with CeO2The preparation method of the NCM ternary cathode material comprises the following steps:
carrying out ultrasonic treatment on cerium nitrate and a ternary positive electrode material NCM in ethanol for 1-2 h, then uniformly grinding, calcining at 500-750 ℃ for 4-6 h, and cooling along with a furnace to obtain a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1);
wherein the chemical formula of the NCM ternary cathode material is Li [ Ni ]1-x-yMnxCoy]O2，x>0，y>0， 0.8<1-x-y<1，0<x+y<0.2；
The molar ratio of Ce to the NCM ternary cathode material in the cerium nitrate is 0.005-0.03: 1.
Preferably, the molar ratio of Ni, Mn and Co in the NCM ternary cathode material is 0.869:0.0921: 0.0389.
Preferably, the molar ratio of cerium nitrate to the NCM ternary positive electrode material is 0.01: 1.
Preferably, the calcination temperature is 600 ℃.
Preferably, the calcination time is 5 h.
The anode material of the lithium ion secondary battery is the surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1).
Has the advantages that:
(1) mixing an NCM ternary positive electrode material with cerous nitrate, dissolving and grinding the mixture by using an ethanol solution, uniformly distributing the cerous nitrate on the surfaces of NCM ternary positive electrode material particles, and calcining the mixture at different temperatures to ensure that one part of Ce enters the inside of a lattice surface layer and the other part of Ce is CeO2Is present on the surface layer of the positive electrode material.
(2) The binding energy between Ce and O is greater than that between other M and O (M ═ Ni, Co, or Mn), so Ce doped in the surface transition metal layer3+The method is beneficial to stabilizing the lattice structure, especially the lattice structure under the high-pressure condition, and the problem of serious oxygen release of the NCM ternary cathode material under the high-pressure condition is solved; ce3+Entering the surface layer crystal lattice to support the stability of the laminated crystal lattice structure; and the original Ce entering the crystal lattice4+Has strong oxidizing property and can transfer Ni to Li layer2+Oxidation to Ni3+The nickel ions are migrated back to the transition metal layer again, the mixed arrangement of the surface layer structure is reduced, the surface layer structure stability of the NCM ternary cathode material is effectively improved, and meanwhile, the Ce is added4+Is reduced to Ce by itself3+Stably exists in a transition metal layer of the NCM ternary cathode material and generates an oxidation-reduction reaction Ce4++Ni2+→Ce3++Ni3+；Ce3+Doping into the transition metal layer of the surface layer to occupy Ni2+Can play a role in supporting the frame, inhibiting the phase transformation of the surface layer structure and inhibiting Li in the electrochemical cycle process+/Ni2+And (4) mixed discharging. In addition, Ce3+Has a relatively large ionic radius (rCe)3+0.102nm), doped into transition goldAfter the sublayer, it helps to broaden Li+Embedding in and out of channels, contributing to the enhancement of Li+The transmission rate of the NCM ternary positive electrode material can obviously improve the electrochemical performance of the NCM ternary positive electrode material under high voltage and high multiplying power (4.5V, more than or equal to 1C).
(3) By controlling the synthesis temperature, CeO is coated on the surface of NCM ternary cathode material particles2，CeO2The direct contact between electrolyte and an electrode can be isolated, the increase speed of interface charge transfer resistance and surface polarization in the electrochemical cycle process is slowed down, and the material shows better thermal stability and cycle stability.
(4) The method has the advantages of wide source of raw materials, low price, simple operation process, easy realization of process and technology, and large-scale commercial application, and can be used for carrying out Ce coating and doping on the surfaces of other ternary anode materials or lithium-rich anode materials.
Drawings
FIG. 1 is an X-ray diffraction (XRD) spectrum of the final products prepared in examples 1-4 and comparative example 1.
Fig. 2 is a Scanning Electron Microscope (SEM) picture of the final product prepared in comparative example 1.
Fig. 3 is an SEM picture of the final product prepared in example 1.
Fig. 4 is an SEM picture of the final product prepared in example 2.
Fig. 5 is an SEM picture of the final product prepared in example 3.
Fig. 6 is an SEM picture of the final product prepared in example 4.
FIG. 7 is an energy spectrum (EDS) profile of the final product prepared in example 3.
FIG. 8 is a Ce3d spectrum in X-ray photoelectron spectroscopy (XPS) testing of the final products prepared in examples 1-4.
Fig. 9 is a Raman spectroscopy (Raman) test spectrum of the final product prepared in example 3.
FIG. 10 is a graph of the XPS test for Ni2p for the final products prepared in examples 1-4 and in the comparative example.
Fig. 11 is a graph of the cycling performance of assembled CR2025 coin cells of examples 1-4 and comparative example 1 at 2.75V to 4.5V voltage intervals and 0.2C (1C ═ 200mAh/g) rate.
Fig. 12 is a graph of the rate performance of assembled CR2025 coin cells of examples 1-4 and assembled CR2025 coin cells of comparative example 1, cycled for 5 weeks at different rates in sequence.
Fig. 13 is a plot of Cyclic Voltammetry (CV) after 1 week and 50 weeks of 2.75-4.5V cycling for the assembled CR2025 coin cell of comparative example 1.
Fig. 14 is a graph of CV after 1 week and 50 weeks of 2.75-4.5V cycling for the assembled CR2025 coin cell of example 1.
Fig. 15 is a graph of CV after 1 week and 50 weeks of 2.75-4.5V cycling for the assembled CR2025 coin cell of example 2.
Fig. 16 is a graph of CV after 1 week and 50 weeks of 2.75-4.5V cycling for the assembled CR2025 coin cell of example 3.
Fig. 17 is a graph of CV after 1 week and 50 weeks of 2.75-4.5V cycling for the assembled CR2025 coin cell of example 4.
Fig. 18 is a graph of the ac impedance (EIS) measurements of assembled CR2025 coin cells of examples 1-4 and comparative example 1 after 50 weeks cycling at 4.3V voltage at the charged state.
Detailed Description
For a better understanding of the present invention, the present invention is described in further detail below with reference to specific examples. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation. Additionally, the endpoints of the ranges and any values disclosed herein are not limited to the precise range or value, and such ranges or values should be understood to encompass values close to those ranges or values. For ranges of values, between the endpoints of each of the ranges and the individual points, and between the individual points may be combined with each other to give one or more new ranges of values, and these ranges of values should be considered as specifically disclosed herein.
In the following examples:
(1) XRD test: an X-ray diffractometer with an instrument model of Rigaku Ultima IV-185, Japan;
(2) and (4) SEM test: scanning electron microscope, instrument model: FEI QUANTA 250, usa;
(3) XPS test: scanning X-ray photoelectron spectrometer (XPS), instrument model is: PHI Quantera II, japan;
(4) raman testing: laser raman spectroscopy, instrument type: renishaw RM 2000;
(5) EDS test: the spectrometer used was an Oxford INCA model ray spectrometer manufactured by Oxford instruments (shanghai) ltd.
(6) Assembling of CR2025 button cell: preparing the positive electrode material prepared in the comparative example or the example, acetylene black and polyvinylidene fluoride (PVDF) into slurry according to the mass ratio of 8:1:1, coating the slurry on an aluminum foil, cutting the dried aluminum foil loaded with the slurry into small round pieces with the diameter of about 1cm by using a cutting machine to be used as a positive electrode, using a metal lithium piece as a negative electrode, using Celgard2300 as a diaphragm and using 1M carbonate solution as an electrolyte (wherein the solvent is a mixed solution of ethylene carbonate and dimethyl carbonate with the volume ratio of 1:1, and the solute is LiPF solute6) Assembling a CR2025 button cell in an argon glove box;
(7) and (3) testing charge and discharge cycles: performing constant-current charge and discharge tests on the assembled CR2025 button cell under different current densities by adopting a CT2001A Alnd cell tester, wherein the current density of 1C is defined to be 200 mA/g, the charge and discharge voltage interval is 2.75V-4.5V, and the test temperature is 25 ℃;
(8) and (3) rate performance test: performing constant current charge and discharge tests for 5 weeks in each circulation at different current densities of 0.1C, 0.2C, 1C, 2C, 5C, 10C and 0.1C respectively, wherein after 2C, 5C and 10C high-rate constant current charging, constant voltage charging is performed for 1 hour or until the current density is less than 0.05C;
(9) and (3) testing alternating current impedance: CHI604c electrochemical workstation, china; the test voltage is 4.5V, the frequency range is 0.01 Hz-0.1 MHz, the amplitude of the sine wave alternating voltage disturbance signal is 5m, and the counter electrode is taken as a reference electrode;
(10) cyclic voltammetry testing: CHI660e electrochemical workstation, china; the test voltage interval is 2V-4.8V, and the scanning speed is 0.1 mV/s.
Examples 1 to 7LiNi0.869Mn0.0921Co0.0389O2Were prepared according to the method described in comparative example 1.
Comparative example 1
(1) Dissolving manganese sulfate, nickel sulfate and cobalt sulfate in deionized water according to the molar ratio of Ni to Mn to Co being 0.869 to 0.0921 to 0.0389 to obtain 2mol/L sulfate water solution;
(2) preparing an alkaline aqueous solution containing 2mol/L sodium carbonate and 2mol/L ammonia water;
(3) continuously adding the prepared sulfate aqueous solution and the prepared alkaline aqueous solution into a reaction kettle which is provided with a stirrer and is filled with nitrogen respectively by using a peristaltic pump, controlling the pH value by adjusting the adding rate of the sulfate aqueous solution or the alkaline aqueous solution to ensure that the pH value is stabilized to 11, controlling the reaction temperature to be 55 ℃, the stirring speed to be 650r/min and adjusting the sample injection speed to be 0.25 mL/min; after the sample introduction is completed, aging is kept for 6 hours in the nitrogen atmosphere, and then the obtained precipitate is filtered, washed and dried to obtain Ni0.869Mn0.0921Co0.0389(OH)2；
(4) Mixing Ni0.869Mn0.0921Co0.0389(OH)2Mixing with LiOH powder according to a molar ratio of 1:1, dry-grinding in a mortar for 25min, adding ethanol, continuously grinding for 25min, placing the mixture of the two in an oxygen atmosphere, calcining at 450 ℃ for 6h, heating to 750 ℃ for 12h, and cooling with a furnace to obtain the NCM ternary cathode material (LiNi)0.869Mn0.0921Co0.0389O2) Abbreviated as NCM.
The XRD test results of NCM are shown in FIG. 1, and the positions of characteristic peaks and LiNiO can be seen2(PDF #09-0063) is completely consistent, and the peak separation between (006)/(012) and (018)/(110) is significant, indicating that the layered structure is good. According to the XRD Rietveld refinement result, Ni2+The occupancy in the Li layer was 2.98%.
The results of the SEM test of NCM are shown in fig. 2, and it can be seen that the NCM material can maintain its spherical morphology with a radius of around 12 microns.
The XPS test of NCM showed the pattern of Ni2p in FIG. 10, and the NCM material contains Ni in large amount2+The form exists.
And assembling the NCM serving as a positive electrode material into a CR2025 button cell, and carrying out corresponding electrochemical performance test.
The charge and discharge performance results of the assembled battery after 50 weeks of circulation under the test conditions of 2.75-4.5V, 25 ℃ and 0.2C are shown in fig. 11, the first week charge capacity is 214mAh/g, the discharge specific capacity is 178.7mAh/g, the first week coulombic efficiency is 83.5%, the discharge capacity after 50 weeks of circulation is 163.5mAh/g, and the capacity retention rate is 91.5%.
The results of the rate performance of the assembled battery at different rates for 5 cycles are shown in fig. 12, where 10C/0.1C is 112.7mAh g-1/177.8mAh·g-1＝63.4％。
The CV curve results of the assembled cell after 50 weeks of 2.75-4.5V cycling are shown in fig. 13, and the redox peaks in the range of 2.5V-4.6V after 50 weeks of cycling are not obvious, indicating that few ions contribute to the capacity of redox inside the material; also shows that the material structure is greatly changed, and the positions for oxidation and reduction are also changed.
Electrochemical impedance test results of the assembled battery after 50 cycles are shown in fig. 18, and it can be seen that the impedance graph includes a semicircle of the high frequency region, which is the interface resistance, a semicircle of the middle frequency region corresponding to the charge transfer resistance, and a straight line of the low frequency region, which is the Warburg resistance. Interfacial resistance R of NCM811 after 50 weeks of cyclingf8.79 Ω, charge transfer resistance Rct＝426.7Ω。
Example 1
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.01:1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 400 ℃, and cooling the mixture along with a furnace to obtain a final product, namely post-Ce-400.
As shown in FIG. 1, it can be seen that the main peak of post-Ce-400 in the present example is substantially identical to the main peak of the comparative example in position, and no hetero-peak phase is generated in the range of 20 to 40 degrees, meaning that no CeO is generated2And (4) generating. According to the XRD Rietveld refinement results, at postIn the Ce-400 sample, Ni2+The atomic percent occupancy in the Li layer was 1.92%, indicating Li+/Ni2+The problem of mixed drainage is improved.
The results of the SEM test of post-Ce-400 are shown in FIG. 3, and it can be seen that the material sample can maintain its spherical morphology with a radius of about 12 microns.
As shown in FIG. 8, the results of the spectrum of Ce3d in XPS test of post-Ce-400 show that the characteristic peak of Ce in XPS spectrum of Ce3d corresponding to post-Ce-400 is not very distinct, and that there are weak peaks corresponding to 888.0eV (V0),885.4eV (V '), 897.8eV (u0), and 903.5eV (u'), which prove that Ce is present3+Exist inside the surface layer lattice. And Ce was not detected as Ce4+The form of ions exists on the surface of the cathode material, and proves that CeO is not generated when the Ce and NCM materials are calcined at 400 DEG C2It is shown that this calcination temperature does not form CeO on the surface of the NCM positive electrode2。
The XPS test of post-Ce-400 showed the pattern of Ni2p in FIG. 10, which shows that Ni is more Ni in NCM material2+While in post-Ce-400 material, Ni is more in the form of Ni3+The form exists. And Ni2p was observed1/2The position of the peak is also clearly shifted towards higher binding energy, indicating that the valence state of Ni is increased. This also demonstrates to some extent Li in post-Ce-400 materials+/Ni2+The mixed ejection is inhibited, that is, the Ce can be proved3+Doping into the surface transition metal layer.
No CeO was seen in the post-Ce-400 Raman test2Corresponding to 464cm-1The presence of a peak at the site further demonstrates the absence of CeO in post-Ce-4002Coating of (2).
And (3) assembling the post-Ce-400 serving as a positive electrode material into the CR2025 button cell, and carrying out electrochemical performance test.
The electrochemical performance results of the assembled battery after 50 weeks of circulation under the test conditions of 2.75-4.5V, 25 ℃ and 0.2C are shown in fig. 11, the first week charging capacity of the NCM material is 214mAh/g, the specific discharge capacity is 178.7mAh/g, the first week coulombic efficiency is 83.5%, the discharge capacity after 50 weeks of circulation is 163.5mAh/g, and the capacity retention rate is 91.5%. The first-cycle charging specific capacity of the post-Ce-400 material is 226mAh/g, the discharging specific capacity is 179.2mAh/g, the first-cycle coulombic efficiency is 79.3%, the discharging specific capacity after 50 cycles is 161mAh/g, and the capacity retention rate is 89.8%.
The results of the performance test of the assembled battery, which was cycled for 5 weeks at different rates, are shown in fig. 12, and 10C/0.1C of the NCM material was 112.7mAh g-1/177.8mAh·g-163.4%. And the 10C/0.1C of post-Ce-400 is 127.8mAh g-1/179.6mAh·g-171.2%. The post-Ce-400 material is more stable in structure, and the capacity retention rate of the post-Ce-400 material circulating under high-rate and high voltage is slightly improved compared with the bulk.
The CV curve results of the assembled cell after 50 cycles at 2.75-4.5V are shown in fig. 14, and in comparison with the CV curve of the NCM material of the comparative example of fig. 13 after 50 cycles, it can be seen that the redox peaks of the Post-Ce-400 sample in the interval of 2.5V-4.6V after 50 cycles are not very obvious, indicating that few ions contribute to redox in the material, and the lower discharge capacity in fig. 11. Also shows that the material structure is greatly changed, and the positions for oxidation and reduction are also changed.
Electrochemical impedance test results of the assembled battery after 50 cycles are shown in fig. 18, and it can be seen that the impedance graph includes a semicircle of the high frequency region, which is the interface resistance, a semicircle of the middle frequency region corresponding to the charge transfer resistance, and a straight line of the low frequency region, which is the Warburg resistance. It can be seen that the interfacial resistance R of Post-Ce-400 after 50 weeks of cycling in example 1 isf8.57 Ω, charge transfer resistance Rct415.7 Ω. The interfacial resistance and charge transfer resistance of the Post-Ce-400 material are not improved or suppressed relative to the unmodified NCM ternary material.
From these analytical data the following conclusions can be drawn: the surface layer of the post-Ce-400 material is doped with Ce3+But no CeO2The electrochemical data result shows that the electrochemical performance of the NCM ternary cathode material is not well improved by the material.
Example 2
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.01:1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 500 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material is marked as post-Ce-500.
The XRD test result of post-Ce-500 is shown in figure 1, the main peak in the embodiment is basically consistent with the main peak position in the comparative example, and in the range of 20-40 degrees, the mixed peak phase CeO is present2Peak formation means that CeO is present on the surface of the material2And (4) generating. Ni in post-Ce-500 samples according to XRD Rietveld refinement2+The atomic percentage occupied in the Li layer was 1.71%, indicating that Li+/Ni2+The problem of mixed drainage is improved.
The results of the SEM test of post-Ce-500 are shown in FIG. 4, and it can be seen that the material sample can maintain its spherical morphology with a radius of around 12 microns.
The EDS spectrum results of post-Ce-500 indicate that Ce is present in the surface layer of the material of post-Ce-500.
The results of the spectrum of Ce3d in XPS test of post-Ce-500 are shown in FIG. 8, from which it can be seen that the characteristic peaks of corresponding Ce in the XPS spectrum of post-Ce-500 corresponding Ce3d are quite distinct, and the peaks of corresponding v, v ', U, U ', U ' at 882.1eV, 888.9eV, 898.1eV, 902.4eV, 907.0eV, 916.2eV indicate that Ce is present in4+I.e. the presence of CeO in the surface layer of the material2. It was confirmed that CeO was formed when Ce and NCM811 were calcined at 500 deg.C2. The XPS spectrum of Ce3d shows peaks at positions 888.0eV (V0),885.4eV (V '), 897.8eV (u0), and 903.5eV (u') corresponding to Ce3+It is also quite clear that the particles of the post-Ce-500 sample proved to have Ce therein3+The ions are present inside the surface layer lattice. Also, it is stated that a calcination temperature of 500 ℃ can be such that Ce is present4+Into the surface lattice of high-nickel material to react with Ni3+Oxidation-reduction reaction Ce occurs4++Ni3+→ Ce3++Ni2+Simultaneously, CeO can be formed on the surface of the high-nickel particles2Protective layerStabilizing the electrolyte/electrode interface and inhibiting the surface Li+/Ni2+And mixed arrangement is carried out, so that the structural stability of the NCM ternary cathode material is improved.
The result of the Ni2p spectrum of XPS test of post-Ce-500 is shown in FIG. 10, and it can be seen that Ni is more Ni than Ni in the NCM material of the comparative example2+While in post-Ce-500 modified materials, Ni is more in the form of Ni3+The form exists. And Ni2p was observed1/2The position of the peak is also clearly shifted towards higher binding energy, indicating that the valence state of Ni is increased. This also demonstrates to some extent Li in post-Ce-500 materials+/Ni2+Mixing and draining are suppressed, and Ce3+Doping into the surface transition metal layer can help the NCM ternary cathode material to maintain stable lattice structure under the condition of high lithium removal state.
In the Raman test of post-Ce-500, the peak corresponds to the binding energy at 464cm-1Corresponding to CeO2And the binding energy is 261cm-1And 560cm-1The peak at (a) is its second order peak.
And (3) assembling the post-Ce-500 serving as a positive electrode material into a CR2025 button cell, and carrying out electrochemical performance test.
The electrochemical performance results of the assembled battery after 50 weeks of circulation under the test conditions of 2.75-4.5V, 25 ℃ and 0.2C are shown in fig. 11, the first week charging capacity of the NCM material is 214mAh/g, the specific discharge capacity is 178.7mAh/g, the first week coulombic efficiency is 83.5%, the discharge capacity after 50 weeks of circulation is 163.5mAh/g, and the capacity retention rate is 91.5%. The first-cycle charging specific capacity of the post-Ce-500 material is 229.4mAh/g, the discharging specific capacity is 190.2mAh/g, the first-cycle coulombic efficiency is 82.9%, the discharging specific capacity after 50 cycles is 186.1 mAh/g, and the capacity retention rate is 97.8%.
The results of the performance test of the assembled battery, which was cycled for 5 weeks at different rates, are shown in fig. 12, and 10C/0.1C of the NCM material was 112.7mAh g-1/177.8mAh·g-163.4%. While the 10C/0.1C ratio of post-Ce-500 is 139.9mAh g-1/189.4mAh·g-173.9%. The post-Ce-500 material is shown to be more stable in structure and can cycle under high-rate and high-voltageThe capacity retention of the rings is improved relative to NCM materials.
The results of the CV curves of the assembled cell after 50 weeks of 2.75-4.5V cycling are shown in fig. 15, and in comparison with the CV curves of the NCM material of the comparative example of fig. 13 after 50 weeks of cycling, it can be seen that the redox peaks of the NCM material in the range of 2.5V-4.6V after 50 weeks of cycling are not readily apparent, indicating that there are few ions within the NCM material that contribute to the redox capacity. In the post-Ce-500 material, the redox peak is still clearly visible, and the maintenance of the layered structure is proved to be better, so that various transition metal ions in the material can still contribute to the capacity through oxidation and reduction in the voltage range of 2.5-4.6V.
Electrochemical impedance test results of the assembled cell after 50 weeks of cycling the material are shown in FIG. 18, which shows the interfacial resistance R of Post-Ce-500 after 50 weeks of cyclingf4.11 Ω, charge transfer resistance Rct382 Ω. It can be seen that the interfacial resistance and charge transfer resistance of Post-Ce-500 are significantly reduced compared to NCM materials.
From these analytical data the following conclusions can be drawn: the surface layer of the post-Ce-500 material is doped with Ce3+And is coated with CeO2The electrochemical performance of the material is obviously improved compared with that of an unmodified NCM ternary cathode material.
Example 3
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.01:1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 600 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary cathode material is marked as post-Ce-600.
The XRD test result of post-Ce-600 is shown in figure 1, the main peak in the embodiment is basically consistent with the main peak position in the comparative example, and in the range of 20-40 degrees, the mixed peak phase CeO is present2Peak formation means that CeO is present on the surface of the material2And (4) generating. Ni in post-Ce-400 samples according to XRD Rietveld refinement results2+The percentage of occupied atoms in the Li layer was 1.46%, and Li was added thereto+/Ni2+The problem of mixed drainage is improved。
The results of the SEM test of post-Ce-600 are shown in FIG. 5, and it can be seen that the material sample can maintain its spherical morphology with a radius of around 12 microns.
The EDS spectrum result of post-Ce-600 is shown in FIG. 7, and Ce can be seen to exist in the surface layer of the material of post-Ce-600.
The results of the spectrum of Ce3d in XPS test of post-Ce-600 are shown in FIG. 8, from which it can be seen that the characteristic peaks of Ce corresponding to the XPS spectrum of Ce3d corresponding to post-Ce-600 are quite distinct, and can be identified by the corresponding peaks of v, v ', U, U', U 'corresponding to Ce', existing at 882.1eV, 888.9eV, 898.1eV, 902.4eV, 907.0eV, 916.2eV4+Present, i.e. CeO is present in the surface layer of the material2. Proves that CeO is generated when the ternary anode material of Ce and NCM is calcined at 600 DEG C2. The XPS spectrum of Ce3d shows peaks at positions 888.0eV (V0),885.4eV (V '), 897.8eV (u0), and 903.5eV (u') corresponding to Ce3+It is also quite obvious that the particles of the post-Ce-600 sample have Ce3+The ions are present inside the surface layer lattice. Also, it is stated that a calcination temperature of 600 ℃ can be used to obtain Ce4+Into the surface lattice of high-nickel material to react with Ni3+Oxidation-reduction reaction Ce occurs4++Ni3+→Ce3++Ni2+Simultaneously, CeO can be formed on the surface of the high-nickel particles2A protective layer for stabilizing the electrolyte/electrode interface and inhibiting Li on the surface layer+/Ni2+And mixed arrangement is carried out, so that the structural stability of the NCM ternary cathode material is improved.
The result of the Ni2p spectrum of XPS test of post-Ce-600 is shown in FIG. 10, and it can be seen that Ni is more Ni than Ni in the NCM material of the comparative example2+While in post-Ce-600 material, Ni is more in the form of Ni3+The form exists. And Ni2p was observed1/2The position of the peak is also clearly shifted towards higher binding energy, indicating that the valence state of Ni is increased. This also demonstrates to some extent Li in the post-Ce-600 material+/Ni2+Mixing and draining are suppressed, and Ce3+Doping into the transition metal layer can help the NCM ternary cathode material to maintain stable lattice structure under the condition of high lithium removal state。
The Raman test result of post-Ce-600 is shown in FIG. 9, and the position of the binding energy corresponding to the Raman test peak is 464cm-1Corresponding to CeO2And the binding energy is 261cm-1And 560cm-1The peak at (a) is its second order peak.
And (3) assembling the post-Ce-600 serving as the positive electrode material into the CR2025 button cell, and carrying out electrochemical performance test.
The electrochemical performance results of the assembled battery after 50 weeks of circulation under the test conditions of 2.75-4.5V, 25 ℃ and 0.2C are shown in fig. 11, the first week charging capacity of the NCM material is 214mAh/g, the specific discharge capacity is 178.7mAh/g, the first week coulombic efficiency is 83.5%, the discharge capacity after 50 weeks of circulation is 163.5mAh/g, and the capacity retention rate is 91.5%. The first-cycle charging specific capacity of the post-Ce-600 material is 229.4mAh/g, the discharging specific capacity is 196.8mAh/g, the first-cycle coulombic efficiency is 80.9%, the discharging specific capacity after 50 cycles is 195.3 mAh/g, and the capacity retention rate is 99.2%.
The results of the performance test of the assembled battery, which was cycled for 5 weeks at different rates, are shown in fig. 12, and 10C/0.1C of the NCM material was 112.7mAh g-1/177.8mAh·g-163.4%. And the 10C/0.1C of post-Ce-600 is 136.6mAh g-1/197mAh·g-169.4%. The post-Ce-600 material is shown to be more stable in structure, and the capacity retention rate of the post-Ce-600 material circulating under high-rate and high-voltage is improved compared with that of an NCM material.
The CV curve results of the assembled cell after 50 weeks of 2.75-4.5V cycling are shown in fig. 16, and in comparison with the CV curve of the NCM material in the comparative example of fig. 13 after 50 weeks of cycling, it can be seen that the redox peaks of the NCM material in the range of 2.5V-4.6V after 50 weeks of cycling are not readily apparent, indicating that there are few ions contributing to the redox within the NCM material. In the post-Ce-600 material, the redox peak is still clearly visible, and the maintenance of the layered structure is proved to be better, so that various transition metal ions in the material can still contribute to the capacity through oxidation and reduction in the voltage range of 2.5-4.6V.
The electrochemical impedance test results of the assembled cell after 50 weeks of cycling for the material are shown in fig. 18And the interfacial resistance R of Post-Ce-600 after 50 weeks of cyclingf4.87 Ω, charge transfer resistance Rct246.3 Ω. It can be seen from the figure that the increase of the resistance is the least after the same period of electrochemical cycling of the interface resistance and the charge transfer resistance of the Post-Ce-600 material, so the structural stability of the Post-Ce-600 material is the best, and the electrochemical cycling stability is the best corresponding to that in FIG. 11.
From these analytical data the following conclusions can be drawn: the surface layer of the post-Ce-600 material is doped with Ce3+And is coated with CeO2The electrochemical performance of the material is obviously improved compared with that of an unmodified NCM ternary cathode material.
Example 4
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.01:1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 750 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1), is noted as post-Ce-750.
The XRD test result of post-Ce-750 is shown in figure 1, the main peak in the embodiment is basically consistent with the main peak position in the comparative example, and in the range of 20-40 degrees, the mixed peak phase CeO is present2The peak formation means that CeO is present on the surface of the high nickel material2And (4) generating. Ni in post-Ce-400 samples according to XRD Rietveld refinement results2+The atomic percentage occupied in the Li layer was 1.66%, indicating that Li+/Ni2+The problem of mixed drainage is improved.
The results of the SEM test of post-Ce-750 are shown in FIG. 6, and it can be seen that the material sample can maintain its spherical morphology with a radius of around 12 microns.
The EDS spectrum results of post-Ce-500 show that Ce is present in the surface layer of the material of post-Ce-600.
The results of the spectrum of Ce3d in XPS test of post-Ce-750 are shown in FIG. 8, from which it can be seen that the characteristic peaks of corresponding Ce in the XPS spectrum of post-Ce-750 corresponding Ce3d are quite distinct, and can be seen by the corresponding v, v ", v ″, existing at 882.1eV, 888.9eV, 898.1eV, 902.4eV, 907.0eV, 916.2eV', U, U ', U ' peaks correspond to Ce4+Present, i.e. CeO is present in the surface layer of the material2. Proves that CeO is generated when the ternary anode material of Ce and NCM is calcined at 750 DEG C2. XPS spectra of Ce3d at positions 888.0eV (V0),885.4eV (V '), 897.8eV (u0), and 903.5eV (u'), corresponding to Ce3+It was confirmed that Ce was contained in the particles of the post-Ce-750 sample3+The ions are present inside the surface layer lattice. Also, it is stated that a calcination temperature of 750 ℃ can be used to obtain Ce4+Into the surface lattice of high-nickel material to react with Ni3+Oxidation-reduction reaction Ce occurs4++Ni3+→Ce3++Ni2+Simultaneously, CeO can be formed on the surface of the high-nickel particles2A protective layer for stabilizing the electrolyte/electrode interface and inhibiting Li on the surface layer+/Ni2+And mixed arrangement is carried out, so that the structural stability of the NCM ternary cathode material is improved.
The Raman test results of post-Ce-750 show that: the position of the binding energy corresponding to the Raman test peak is 464cm-1Corresponding to CeO2And the binding energy is 261cm-1And 560cm-1The peak at (a) is its second order peak.
XPS test of post-Ce-750 showed the result of Ni2p spectrum shown in FIG. 10, and it can be seen that Ni is more Ni than Ni in the NCM material of the comparative example2+While in post-Ce-750 material, Ni is more in the form of Ni3+The form exists. And Ni2p was observed1/2The position of the peak is also clearly shifted towards higher binding energy, indicating that the valence state of Ni is increased. This also demonstrates to some extent Li in post-Ce-750 materials+/Ni2+Mixing and draining are suppressed, and Ce3+Doping into the transition metal layer can help the NCM ternary cathode material to maintain stable lattice structure under the condition of high lithium removal state.
And (3) assembling the post-Ce-750 serving as a positive electrode material into a CR2025 button cell, and carrying out electrochemical performance test.
The electrochemical performance results of the assembled battery after 50 weeks of circulation under the test conditions of 2.75-4.5V, 25 ℃ and 0.2C are shown in fig. 11, the first week charging capacity of the NCM material is 214mAh/g, the specific discharge capacity is 178.7mAh/g, the first week coulombic efficiency is 83.5%, the discharge capacity after 50 weeks of circulation is 163.5mAh/g, and the capacity retention rate is 91.5%. The first-cycle charging specific capacity of the post-Ce-750 material is 248.9mAh/g, the discharging specific capacity is 199.1mAh/g, the first-cycle coulombic efficiency is 80%, the discharging specific capacity after 50 cycles is 189 mAh/g, and the capacity retention rate is 94.9%.
The results of the performance test of the assembled battery, which was cycled for 5 weeks at different rates, are shown in fig. 12, and 10C/0.1C of the NCM material was 112.7mAh g-1/177.8mAh·g-163.4%. While the 10C/0.1C of post-Ce-750 is 142.7mAh g-1/210.4mAh·g-167.8%. The post-Ce-750 material is shown to be more stable in structure, and the capacity retention rate of the post-Ce-750 material circulating under high-rate and high-voltage is improved compared with that of an NCM material.
The results of the CV curves of the assembled cell after 50 weeks of 2.75-4.5V cycling are shown in fig. 17, and in comparison with the CV curves of the NCM material of the comparative example of fig. 13 after 50 weeks of cycling, it can be seen that the redox peaks of the NCM material in the range of 2.5V-4.6V after 50 weeks of cycling are not readily apparent, indicating that there are few ions within the NCM material that contribute to the redox capacity. In the post-Ce-750 material, the redox peak is still clearly visible, which proves that the layered structure is better maintained, so that various transition metal ions in the material can still contribute to the capacity through redox in the voltage range of 2.5-4.6V. Meanwhile, in a CV curve, the voltage difference of the redox peak of the post-Ce-750 material is not large, and the corresponding polarization along with electrochemical circulation is not large.
Electrochemical impedance test results of the assembled cell after 50 weeks of cycling the material are shown in FIG. 18, which shows the interfacial resistance R of Post-Ce-750 after 50 weeks of cyclingf5.55 Ω, charge transfer resistance Rct393.3 Ω. The interfacial resistance and charge transfer resistance of the post-Ce-750 material after 50 weeks of cycling was significantly reduced compared to the NCM material. The material modified by Ce is more stable, and the impedance is slowly increased in the electrochemical circulation process.
From these analytical data the following conclusions can be drawn: the surface layer of the post-Ce-750 material is doped with Ce3+And is coated with CeO2The electrochemical performance of the material is obviously improved compared with that of an unmodified NCM ternary cathode material.
Example 5
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.005: 1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 500 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1).
The material prepared in the embodiment is used as a positive electrode material to be assembled into a CR2025 button cell, and an electrochemical performance test is carried out. Constant-current charge and discharge tests are carried out at a voltage range of 2.75V-4.5V, 25 ℃ and 0.2C multiplying power, the first-cycle discharge capacity is 193.2mAh/g, the discharge capacity after 50-cycle circulation is 178.7mAh/g, and the capacity retention rate is 92.5%.
Example 6
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.02: 1, adding the mixture into ethanol, performing ultrasonic treatment for 1 hour, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 500 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1).
The material prepared in the embodiment is used as a positive electrode material to be assembled into a CR2025 button cell, and an electrochemical performance test is carried out. Constant-current charge and discharge tests are carried out at a voltage range of 2.75V-4.5V, 25 ℃ and 0.2C multiplying power, the first-week discharge capacity is 196.3mAh/g, the discharge capacity after 50-week circulation is 179.8mAh/g, and the capacity retention rate is 91.6%.
Example 7
And (2) mixing cerium nitrate and NCM according to a molar ratio Ce: NCM ═ 0.03:1, adding the mixture into ethanol, performing ultrasonic treatment for 2 hours, then mixing and grinding the mixture uniformly by using the ethanol in a mortar, calcining the mixture for 5 hours at the temperature of 500 ℃, and cooling the mixture along with a furnace to obtain a final product, namely a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1).
The material prepared in the embodiment is used as a positive electrode material to be assembled into a CR2025 button cell, and an electrochemical performance test is carried out. Constant-current charge and discharge tests are carried out at a voltage range of 2.75V-4.5V, 25 ℃ and 0.2C multiplying power, the first-week discharge capacity is 189.7mAh/g, the discharge capacity after 50-week circulation is 178.2mAh/g, and the capacity retention rate is 93.9%.
Experiments prove that the surface of a sample with the calcination temperature of 500-750 ℃ can be detected to have Ce by test means such as XRD (X-ray diffraction), XPS (X-ray diffraction), Raman and the like3+And CeO2Exist and can be concluded by electrochemical tests that the surface layer is doped with Ce3+And is coated with CeO2The discharge capacity and the cycle stability of the NCM ternary cathode material are obviously improved. It can also be seen from CV and EIS tests that the surface layer is doped with Ce3+And is coated with CeO2The NCM ternary positive electrode material has a more stable structure and smaller polarization after electrochemical circulation, and has relatively smaller uncompensated resistance and interface charge transfer resistance.
According to the test results of the comparative example and the example, CeO is generated on the surface layer of the NCM ternary cathode material by controlling the synthesis conditions2And Ce is3+Method for doping into transition metal layer of surface crystal lattice, Ce with strong oxidizing property4+Firstly, the reaction solution enters the interior of the high nickel layered structure to generate the oxidation reduction reaction Ce4++Ni2+→Ce3++Ni3+Ni in the surface layer of the crystal lattice2+Oxidation to Ni3+At the same time Ce4+Reduction by itself to Ce3+Stably exists in the transition metal layer, plays a role in stabilizing a layered framework structure and simultaneously reduces Li in the surface layer of the anode material+/Ni2+The function of (1); surface layer CeO2The coating stabilizes the electrolyte/electrode interface structure; the method can obviously improve the rate capability and the cycling stability of the NCM ternary cathode material, especially has better and obvious effect on improving the electrochemical performance under high voltage and high rate, and has the advantages of low cost of raw materials, no toxicity, environmental protection, simple, efficient and environment-friendly whole process flow, wide experimental conditions, high reliability and good industrial application prospect.
The present invention includes, but is not limited to, the above embodiments, and any equivalent substitutions or partial modifications made under the principle of the spirit of the present invention should be considered as being within the scope of the present invention.

Claims (6)

1. Surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary cathode material is characterized in that: the chemical formula of the material is wCeO2-Li [Ni1-x-y-zMnxCoyCez]O2Wherein x is>0，y>0，z>0，w>0，0.8<1-x-y-z<1，0<x+y+z<0.2，0.005≤w+z≤0.03；
The material is prepared by the following method, and the method comprises the following steps:
carrying out ultrasonic treatment on cerium nitrate and a ternary positive electrode material NCM in ethanol for 1-2 h, then uniformly grinding, calcining at 500-750 ℃ for 4-6 h, and cooling along with a furnace to obtain a surface layer doped with Ce3+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1);
wherein the chemical formula of the NCM ternary cathode material is Li [ Ni ]1-x-yMnxCoy]O2，x>0，y>0，0.8<1-x-y<1，0<x+y<0.2；
The molar ratio of Ce to the NCM ternary cathode material in the cerium nitrate is 0.005-0.03: 1.
2. The surface-doped Ce of claim 13+And the surface layer is coated with CeO2The NCM ternary cathode material is characterized in that: the molar ratio of Ni, Mn and Co in the NCM ternary cathode material is 0.869:0.0921: 0.0389.
3. The surface-doped Ce of claim 13+And the surface layer is coated with CeO2The NCM ternary cathode material is characterized in that: the molar ratio of the cerium nitrate to the NCM ternary cathode material is 0.01: 1.
4. The surface-doped Ce of claim 13+And the surface layer is coated with CeO2The NCM ternary cathode material is characterized in that: the calcination temperature was 600 ℃.
5. As in claimA surface layer doped with Ce as set forth in claim 13+And the surface layer is coated with CeO2The NCM ternary cathode material is characterized in that: the calcination time was 5 h.
6. A lithium ion secondary battery characterized in that: the anode material of the battery is the surface layer doped with Ce of claim 13+And the surface layer is coated with CeO2The NCM ternary positive electrode material of (1).
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