CN109449378B - Composite positive electrode material of lithium ion battery and preparation method thereof - Google Patents

Composite positive electrode material of lithium ion battery and preparation method thereof Download PDF

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CN109449378B
CN109449378B CN201811044712.8A CN201811044712A CN109449378B CN 109449378 B CN109449378 B CN 109449378B CN 201811044712 A CN201811044712 A CN 201811044712A CN 109449378 B CN109449378 B CN 109449378B
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lithium
phosphate
ternary material
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CN109449378A (en
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董彬彬
黄震雷
田娜
韩坤明
杨新河
周恒辉
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Pulead Technology Industry Co ltd
Beijing Taifeng Xianxing New Energy Technology Co ltd
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Beijing Taifeng Xianxing New Energy Technology Co ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention provides a composite anode material of a lithium ion battery, which comprises a ternary material matrix LiNixCoyM1‑x‑yO2The iron phosphate transition layer and the lithium iron phosphate coating layer are coated on the surface of the matrix, and the lithium iron phosphate coating layer is coated on the surface of the iron phosphate transition layer; the general formula of the composite cathode material is represented as follows: LiNixCoyM1‑x‑yO2·aFePOz·bLiFePO4. The invention also provides a preparation method of the lithium ion battery composite anode material, which comprises the following steps: adding iron salt and phosphate into water to obtain a uniform dispersion liquid; adding the ternary material into a dispersion medium to obtain a uniform suspension; further obtaining slurry with the two liquids uniformly mixed, drying to obtain a precursor, and sintering to obtain the ferric phosphate coated ternary material; and uniformly mixing the lithium ion battery positive electrode material with a lithium salt and a carbon source, and sintering in an inert atmosphere to obtain the lithium ion battery composite positive electrode material.

Description

Composite positive electrode material of lithium ion battery and preparation method thereof
Technical Field
The invention belongs to the technical field of lithium ion battery materials, and particularly relates to a lithium ion battery composite anode material with a core-shell structure and a preparation method thereof.
Background
At present, lithium iron phosphate and ternary materials are widely applied to the preparation of the anode material of the lithium ion battery in the electric automobile. Although lithium iron phosphate has the advantages of high safety and long cycle life, the energy density is obviously low. Nickel-cobalt-manganese ternary materials are receiving more and more attention due to higher specific energy, and the capacity of the ternary materials is higher and higher with the increase of the nickel content. However, as the content of nickel increases, the structural stability of the nickel is increasingly poor, the cycle life is shorter, and the safety performance is increasingly poor.
The modification of ternary materials, especially ternary materials with high nickel content, is mainly improved by means of doping, cladding and the like. There are also researchers who improve cycling and safety issues through the mixed use of lithium iron phosphate and ternary materials. In patent CN104300123A, lithium iron phosphate and ternary material are mixed during homogenization, and finally, a positive plate is obtained. However, in the patent, the lithium iron phosphate and the ternary material are only physically mixed in the slurry mixing stage, and the two materials are only combined together through physical adsorption, so that the lithium iron phosphate and the ternary material are easy to delaminate in the slurry mixing stage, and the coating uniformity is difficult to ensure, so that the improvement on the cycle performance is limited.
The chinese patent application publication No. CN107546379A discloses that lithium manganese iron phosphate is coated on the surface of the ternary material by a mechanical fusion method and the addition of a binder, although the binding force between the ternary material and the lithium manganese iron phosphate is improved to some extent. However, in the patent, the lithium manganese iron phosphate and the ternary material are still in point contact through the surface point, and are combined through physical bonding force, so that a very firm and effective coating layer cannot be formed, and meanwhile, due to the addition of the binder between the ternary material and the lithium manganese iron phosphate, the transmission of electrons between the ternary material and the lithium manganese iron phosphate can be influenced, so that the electrochemical performance is influenced.
Zhongzhen Wu et al (Wu Z, Ji S, Liu T, et alx Mny Coz)O2@LiFePO4Enhances Its High Voltage Cycling Stability as Li-ion Battery Cathode[J]Nano letters,2016,16(10):6357-The bonding force between the two is improved by the heat treatment, the two are mainly combined through the electrostatic adsorption effect, and the improvement of the bonding force between the two is limited by the simple low-temperature treatment, so that the risk of insufficient bonding force exists;
the two Chinese patent applications with publication numbers of CN105406069A and CN105355880A synthesize lithium iron manganese phosphate or lithium iron phosphate in situ on the surface of the ternary material, and the phosphate coating layer coated by the method is relatively uniform, but the ternary material is easy to react with the lithium iron manganese phosphate or the lithium iron phosphate and the contained carbon coating layer at high temperature under the condition of higher sintering temperature in the process of synthesizing the phosphate coating layer, so that the damage of the surface structure of the material is caused, and the method is difficult to realize industrial production.
Kim et al (Kim S B, Lee K J, Choi W J, et al preparation and cycle performance at high temperature for Li [ Ni0.5Co0.2Mn0.3]O2coated with LiFePO4[J]Journal of Solid State Electrochemistry,2010,14(6):919-922) is used for coating lithium iron phosphate on the surface of the ternary material by a dry coating system to improve the cycle performance of the material, although the high-strength instrument can improve the bonding force between the ternary material and the lithium iron phosphate to a certain extent, the instrument needs to carry out heat treatment on the ternary material and the lithium iron phosphate at high temperature, and the risk of reaction between the ternary material and the lithium iron phosphate exists.
None of the methods provided by the above patent documents provides an effective means of coating to improve cycle and safety issues.
Disclosure of Invention
The invention aims to overcome the defects of the existing long-cycle high-nickel ternary material preparation technology and provides a long-cycle lithium ion battery composite positive electrode material and a preparation method thereof. According to the invention, the surface of the ternary material is coated with the ferric phosphate by an in-situ synthesis method, and the lithium salt and the carbon source are added to form the iron phosphate transition layer and the lithium iron phosphate coating layer on the surface of the ternary material, so that a multi-layer coated core-shell structure is formed. The complete coating layer can effectively avoid direct contact of the ternary material and electrolyte, and the cycle performance and the structural stability of the material are improved.
In order to achieve the purpose, the invention adopts the following technical scheme:
a composite positive electrode material for Li-ion battery is composed of three-element material matrix LiNixCoyM1-x-yO2The iron phosphate transition layer and the lithium iron phosphate coating layer are coated on the surface of the matrix, and the lithium iron phosphate coating layer is coated on the surface of the iron phosphate transition layer;
the general formula of the lithium ion battery composite positive electrode material is represented as follows: LiNixCoyM1-x-yO2·aFePOz·bLiFePO4；
Wherein, the M element is one of Mn, Al, Mg, Zr and Ti; x is more than or equal to 0.6 and less than 1.0, y is more than 0 and less than 0.4, and x + y is less than 1; a is more than or equal to 0.0032 and less than or equal to 0.01286, b is more than or equal to 0.0061 and less than or equal to 0.2442, and z is more than or equal to 3.5 and less than or equal to 4.
Preferably, the atomic number ratio of the ternary material Ni to Co to M comprises 6:2:2, 8:1:1, 9:0.5: 0.5.
Furthermore, the median particle size of the secondary particles of the ternary material is 2-50 μm.
A preparation method of the composite anode material of the lithium ion battery comprises the following steps:
adding iron salt and phosphate into water, and uniformly stirring to obtain a dispersion liquid;
adding a ternary material into a dispersion medium, and uniformly stirring to obtain a suspension, wherein the ternary material is LiNixCoyM1-x-yO2Wherein the M element is one of Mn, Al, Mg, Zr and Ti, and x is more than or equal to 0.6<1.0，0<y<0.4，x+y<1；
Adding the dispersion liquid into the suspension under the condition of stirring, and uniformly stirring to obtain slurry;
drying the slurry to obtain a precursor, and sintering the precursor in a certain atmosphere to obtain a ternary material coated by the ferric phosphate;
and uniformly mixing the ferric phosphate-coated ternary material, lithium salt and a carbon source, and sintering in an inert atmosphere to obtain the lithium ion battery composite anode material.
Further, the ferric salt is at least one of ferric nitrate, ferric chloride and ferric citrate, and the phosphate is at least one of diammonium hydrogen phosphate, ammonium phosphate and ammonium dihydrogen phosphate.
Further, the molar ratio of the iron salt to the phosphate is 1: 1.
Further, the concentration of the iron salt is 0.04-2 mol/L.
Further, the dispersion medium is at least one of ethanol, propanol, methanol and water.
Further, the solid content of the suspension is 10-70%;
further, the molar ratio of the iron salt to the ternary material is (0.0096-0.2652): 1.
Further, the sintering temperature of the precursor is 350-800 ℃, and the sintering time is 0.1-20 h;
further, the drying mode is spray drying, rake drying, heating stirring drying, rotary evaporation drying, flash evaporation drying or vacuum drying.
Further, the lithium salt is at least one of lithium carbonate and lithium hydroxide.
Further, the carbon source is at least one of ascorbic acid, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene butadiene rubber, starch, lactose, sucrose, rock candy, glucose, citric acid and phenolic resin.
Further, the molar ratio of the ternary material to lithium in the lithium salt is 1 (0.0061-0.2442); the mass ratio of the carbon source to the iron phosphate-coated ternary material is (0.5-20): 100.
Further, the inert atmosphere is nitrogen, carbon dioxide or argon.
Further, the sintering temperature is 400-850 ℃ under the inert atmosphere, and the sintering time is 1-20 h.
The invention has the following advantages:
according to the invention, the iron phosphate transition layer and the lithium iron phosphate coating layer are uniformly coated on the surface of the ternary material, so that the direct contact between the ternary material and the electrolyte can be effectively reduced, and the structural stability of the material is improved; the iron phosphate transition layer can tightly combine the ternary material and the lithium iron phosphate, the iron phosphate transition layer can effectively isolate the direct contact between the ternary material and the lithium iron phosphate, and the lithium iron phosphate and the ternary material can react at high temperature to damage the structures of the ternary material and the lithium iron phosphate; the alkali content of the whole material can be effectively reduced and the processing performance of the material can be improved by coating the iron phosphate transition layer on the surface of the ternary material.
Drawings
Fig. 1A to 1B are SEM images of the ternary material used in example 1 and the composite cathode material obtained.
Fig. 2 is a graph of the cycling performance at 60 ℃ of the ternary material used in example 1 and the composite positive electrode material obtained.
Fig. 3 is a graph showing DSC test results of the ternary material used in example 1 and the composite positive electrode material sheet obtained.
Detailed Description
The present invention is described in further detail below by way of examples, which are not intended to limit the present invention, and those skilled in the art can make various modifications or improvements based on the basic idea of the present invention without departing from the scope of the present invention.
Example 1
1) 10.76g of ferric chloride and 8.76g of diammonium phosphate were added to 132g of water and dissolved to obtain a transparent solution, and 100g of a ternary material (LiNi)0.6Co0.2Mn0.2O2) Adding the solution into absolute ethyl alcohol to prepare a suspension with the solid content of 20%, and then adding the solution into the suspension to obtain slurry;
2) spray drying the obtained slurry, and controlling the temperature of an air outlet at 100 ℃; carrying out heat treatment on the material obtained by spray drying at 800 ℃ for 2h in an air atmosphere to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 2.33g of lithium carbonate and 0.55g of rock candy by using a three-dimensional mixer to obtain an intermediate product;
4) sintering the intermediate product at 700 ℃ for 5h in a nitrogen atmosphere to obtain the lithium ion battery composite positive electrode material with the chemical formula of LiNi0.6Co0.2Mn0.2O2·0.0032FePO3.8·0.061LiFePO4。
The used ternary material and the obtained composite cathode material are observed by a scanning electron microscope, and the results are shown in fig. 1A and fig. 1B, and the surface of the composite cathode material is completely coated with a layer of new substance. Compared with the traditional physical mixed coating, the coating layer disclosed by the invention is tightly coated on the surface of the ternary material by a chemical synthesis method, and has the advantages of tight bonding force and more complete coating.
The used ternary material and the obtained composite positive electrode material are subjected to capacity test and pole piece DSC test, a button cell is adopted in the experiment, and the electrode piece and the battery are manufactured and are subjected to charge-discharge detection as follows:
the positive electrode uses N-methyl pyrrolidone as a solvent, and the weight ratio of active substances is as follows: conductive carbon black: preparing slurry from polyvinylidene fluoride (95: 5: 5) and uniformly coating the slurry on an aluminum foil; the negative electrode of the button cell uses a lithium sheet, and the electrolyte is 1mol/L LiPF6Ethylene Carbonate (EC) -dimethyl carbonate (DMC) (mass ratio of EC and DMC 1:1), assembled into button cells in an argon-protected glove box; testing the charge-discharge specific capacity of the material under the multiplying power of 0.1C under the voltage of 2.8-4.25V; testing the cycle retention rate of the material at 60 ℃ under 2.8-4.25V at 1C multiplying power for 300 weeks; testing a pole piece by DSC: charging the pole piece to 4.25-4.6V, disassembling the button cell, cleaning the positive pole piece by using dimethyl carbonate, scraping active substances from the positive pole piece by using a scraper in a glove box, placing 8 mu g of sample in a crucible special for DSC test, adding 8 mu L of electrolyte, sealing, carrying out DSC test, and increasing the temperature at a rate of 5 ℃/min.
The ternary material used and the composite cathode material obtained were subjected to cycle testing at 60 ℃ at a magnification of 1C, and the results are shown in fig. 2, and the cycle retention rates at 300 cycles of the ternary material and the composite cathode material were 82% and 89.8%, respectively. The cycle retention rate of the coated composite cathode material is obviously improved, which shows that the structural stability of the material is improved.
The test result of this example is shown in fig. 3, and it can be seen that the DSC exothermic peak position of the composite cathode material is shifted backward by 26 ℃ relative to the DSC exothermic peak position of the nickel-cobalt-manganese material. Further, after the lithium iron phosphate with the olivine structure with a more stable structure is coated, the contact between the electrolyte and the ternary material can be effectively isolated, and the structural stability of the composite anode material is remarkably improved.
The used ternary material and the obtained composite anode material are subjected to 0.1C capacity test, the discharge specific capacities of the ternary material and the obtained composite anode material are 171.1mAh/g and 168.6mAh/g respectively, and although the capacity is reduced after coating, the cycle performance and the safety performance are improved.
Example 2
1) 7.9g (nonahydrate) of ferric nitrate and 2.25g of ammonium dihydrogen phosphate were added to 489g of water to dissolve them to obtain a transparent solution, and 100g of a ternary material (LiNi)0.8Co0.1Mn0.1O2) Adding the solution into absolute ethyl alcohol to prepare a suspension with the solid content of 70%, and then adding the solution into the suspension to obtain slurry;
2) carrying out rotary evaporation drying on the obtained slurry, and carrying out heat treatment on the dried material at 350 ℃ for 20h in an air atmosphere to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 0.23g of lithium carbonate and 0.8g of polyethylene glycol by using a three-dimensional mixer to obtain an intermediate product;
4) sintering the intermediate product for 20 hours at 400 ℃ in a carbon dioxide atmosphere to obtain the lithium ion battery composite positive electrode material with the chemical formula of LiNi0.8Co0.1Mn0.1O2·0.0129FePO4·0.0061LiFePO4。
The used ternary material and the obtained composite positive electrode material are subjected to cycle test of 1C multiplying power at 60 ℃, and the 300-cycle retention rates of the ternary material and the composite positive electrode material are 66.3% and 86.8% respectively.
And performing pole piece DSC test on the used ternary material and the obtained composite positive electrode material, wherein the result shows that the DSC exothermic peak position of the composite positive electrode material is shifted backwards by 13 ℃ relative to the DSC exothermic peak position of the nickel-cobalt-manganese material.
Example 3
1) 43.29g of iron nitrate (nonahydrate) and 43.02g of ammonium phosphate were added to 265g of water and dissolved to obtain a transparent solution, and 100g of a ternary material (LiNi)0.82Co0.1Al0.08O2) Adding the solution into water to prepare a suspension with the solid content of 40%, and then adding the solution into the suspension to obtain slurry;
2) spray drying the obtained slurry, and carrying out heat treatment on the dried material at 600 ℃ in an air atmosphere for 1h to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 10.57g (monohydrate) of lithium hydroxide and 11g of glucose by using a ball mill to obtain an intermediate product;
4) sintering the intermediate product for 10 hours at 600 ℃ in argon atmosphere to obtain the lithium ion battery composite positive electrode material with the chemical formula of LiNi0.82Co0.1Al0.08O2·0.0129FePO3.9·0.2442LiFePO4。
The ternary material and the composite cathode material are subjected to cycle test of 1C multiplying power at 60 ℃, and the 300-cycle retention rates of the ternary material and the composite cathode material are 65.6% and 91.5%, respectively.
And performing pole piece DSC test on the used ternary material and the obtained composite positive electrode material, wherein the result shows that the DSC exothermic peak position of the composite positive electrode material is shifted back by 32 ℃ relative to the DSC exothermic peak position of the nickel-cobalt-manganese material.
Example 4
1) 32.48g of iron nitrate (nonahydrate) and 17.51g of ammonium dihydrogen phosphate were added to 66g of water to dissolve them to obtain a transparent solution, and 100g of a ternary material (LiNi)0.88Co0.06Mg0.06O2) Adding into methanol to prepare suspension with solid content of 10%, and adding the solution into the suspension to obtain slurry；
2) Heating, stirring and drying the obtained slurry, and carrying out heat treatment on the dried material at 550 ℃ in an air atmosphere for 2h to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 5.29g (monohydrate) of lithium hydroxide and 9g of citric acid by using a super mixer to obtain an intermediate product;
4) sintering the intermediate product for 15 hours at 770 ℃ in argon atmosphere to obtain the lithium ion battery composite anode material with the chemical formula of LiNi0.88Co0.06Mg0.06O2·0.0064FePO3.9·0.1221LiFePO4。
The ternary material and the composite cathode material are subjected to cycle test of 1C multiplying power at 60 ℃, and the 300-cycle retention rates of the ternary material and the composite cathode material are 55.8% and 93.6% respectively.
And performing pole piece DSC test on the used ternary material and the obtained composite cathode material, wherein the result shows that the DSC exothermic peak position of the composite cathode material is shifted back by 29 ℃ relative to the DSC exothermic peak position of the nickel-cobalt-manganese material.
Example 5
1) 1.18g of ferric citrate, 1.94g (nonahydrate) of ferric nitrate and 1.27g of diammonium phosphate were added to 96g of water to be dissolved in water to obtain a transparent solution, and 100g of a ternary material (LiNi)0.83Co0.1Al0.07O2) Adding the solution into water to prepare a suspension with the solid content of 55%, and then adding the solution into the suspension to obtain slurry;
2) spray drying the obtained slurry, and carrying out heat treatment on the dried material at 800 ℃ in an air atmosphere for 0.1h to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 0.26g (monohydrate) of lithium hydroxide and 6.00g of glucose by using a ball mill to obtain an intermediate product;
4) sintering the intermediate product for 10 hours at 600 ℃ in argon atmosphere to obtain the lithium ion battery composite positive electrode material with the chemical formula of LiNi0.82Co0.1Al0.08O2·0.0032FePO3.9·0.0061LiFePO4。
The ternary material and the composite cathode material are subjected to cycle test of 1C multiplying power at 60 ℃, and the 300-cycle retention rates of the ternary material and the composite cathode material are 64.8% and 82.5%, respectively.
And performing pole piece DSC test on the used ternary material and the obtained composite cathode material, wherein the result shows that the DSC exothermic peak position of the composite cathode material is shifted 5 ℃ backwards relative to the DSC exothermic peak position of the nickel-cobalt-manganese material.
Example 6
1) 42.19g (nonahydrate) of iron nitrate, 6.00g of ammonium dihydrogen phosphate and 6.90g of diammonium hydrogen phosphate were added to 104g of water and dissolved to obtain a transparent solution, and 100g of a ternary material (LiNi)0.9Co0.0.5Mn0.05O2) Adding the solution into absolute ethyl alcohol to prepare a suspension with the solid content of 30%, and then adding the solution into the suspension to obtain slurry;
2) carrying out rotary evaporation drying on the obtained slurry, and carrying out heat treatment on the dried material for 1h at 650 ℃ in an air atmosphere to obtain a ternary material with the surface coated with the iron phosphate;
3) uniformly mixing the obtained ternary material with the surface coated with the iron phosphate, 1.75g of lithium carbonate, 1.98g of lithium hydroxide monohydrate and 23.2g of citric acid by using a three-dimensional mixer to obtain an intermediate product;
4) sintering the intermediate product for 1h at 850 ℃ in a nitrogen atmosphere to obtain the lithium ion battery composite positive electrode material with the chemical formula of LiNi0.8Co0.1Mn0.1O2·0.0096FePO4·0.0916LiFePO4。
The ternary material and the composite cathode material are subjected to cycle test of 1C multiplying power at 60 ℃, and the 300-cycle retention rates of the ternary material and the composite cathode material are 63.5% and 87.2%, respectively.
And performing pole piece DSC test on the used ternary material and the obtained composite cathode material, wherein the result shows that the DSC exothermic peak position of the composite cathode material is shifted back by 12 ℃ relative to the DSC exothermic peak position of the nickel-cobalt-manganese material.
In the above embodiments, the ternary material used is compared with the obtained composite cathode material, and the cycle retention rate of the ternary material and the cycle retention rate of the composite cathode material at 60 ℃ under 1C rate cycle test are both smaller than that of the ternary material under 300 cycles, which indicates that the cycle retention rate of the composite cathode material prepared by the method of the present invention is significantly improved, and the structural stability of the material is improved. The used ternary material and the obtained composite positive electrode material are subjected to pole piece DSC tests, and the results show that the DSC exothermic peak position of the composite positive electrode material is shifted backwards relative to the DSC exothermic peak position of the nickel-cobalt-manganese material, which shows that the coated composite positive electrode material can effectively isolate the contact between the electrolyte and the ternary material, and can obviously improve the structural stability.

Claims (10)

1. A composite positive electrode material for Li-ion battery is composed of three-element material matrix LiNixCoyM1-x-yO2The iron phosphate transition layer and the lithium iron phosphate coating layer are coated on the surface of the ternary material matrix, and the lithium iron phosphate coating layer is coated on the surface of the iron phosphate transition layer;
the general formula of the lithium ion battery composite positive electrode material is represented as follows: LiNixCoyM1-x-yO2·aFePOz·bLiFePO4；
Wherein, the M element is one of Mn, Al, Mg, Zr and Ti; x is more than or equal to 0.6 and less than 1.0, y is more than 0 and less than 0.4, and x + y is less than 1; a is more than or equal to 0.0032 and less than or equal to 0.01286, b is more than or equal to 0.0061 and less than or equal to 0.2442, and z is more than or equal to 3.5 and less than or equal to 4.
2. The lithium ion battery composite positive electrode material of claim 1, wherein the atomic number ratio of Ni to Co to M of the ternary material matrix is 6:2:2, 8:1:1, or 9:0.5: 0.5.
3. The composite positive electrode material for the lithium ion battery according to claim 1, wherein the secondary particles of the ternary material matrix have a median particle size of 2 to 50 μm.
4. A preparation method of a composite anode material of a lithium ion battery comprises the following steps:
adding iron salt and phosphate into water, and uniformly stirring to obtain a dispersion liquid;
adding a ternary material into a dispersion medium, and uniformly stirring to obtain a suspension, wherein the ternary material is LiNixCoyM1-x-yO2Wherein the M element is one of Mn, Al, Mg, Zr and Ti, and x is more than or equal to 0.6<1.0，0<y<0.4，x+y<1；
Adding the dispersion liquid into the suspension under the condition of stirring, and uniformly stirring to obtain slurry;
drying the slurry to obtain a precursor, and sintering the precursor in a certain atmosphere to obtain a ternary material coated by the ferric phosphate;
uniformly mixing the ferric phosphate-coated ternary material with a lithium salt and a carbon source, sintering in an inert atmosphere, and uniformly coating an iron phosphate transition layer and a lithium iron phosphate coating layer on the surface of the ternary material to obtain a lithium ion battery composite positive electrode material; the general formula of the lithium ion battery composite positive electrode material is represented as follows: LiNixCoyM1-x-yO2·aFePOz·bLiFePO4(ii) a Wherein a is more than or equal to 0.0032 and less than or equal to 0.01286, b is more than or equal to 0.0061 and less than or equal to 0.2442, and b is more than or equal to 3.5<z≤4。
5. The method according to claim 4, wherein the iron salt is at least one of ferric nitrate, ferric chloride and ferric citrate, the phosphate is at least one of diammonium hydrogen phosphate, ammonium phosphate and ammonium dihydrogen phosphate, the lithium salt is at least one of lithium carbonate and lithium hydroxide, the carbon source is at least one of ascorbic acid, polyvinylidene fluoride, polytetrafluoroethylene, carboxymethyl cellulose, styrene butadiene rubber, starch, lactose, sucrose, rock candy, glucose, citric acid and phenolic resin, and the dispersion medium is at least one of ethanol, propanol, methanol and water.
6. The method according to claim 4 or 5, wherein the molar ratio of the iron salt to the phosphate is 1:1, the concentration of the iron salt is 0.04-2 mol/L, the molar ratio of the iron salt to the ternary material is 0.0096-0.2652: 1, the molar ratio of the iron phosphate-coated ternary material to the lithium salt is 1: 0.0061-0.2442, and the mass ratio of the carbon source to the iron phosphate-coated ternary material is 0.5-20: 100.
7. The method of claim 4, wherein the suspension has a solids content of 10% to 70%.
8. The method according to claim 4, wherein the sintering temperature of the precursor is 350-800 ℃, and the sintering time of the precursor is 0.1-20 h.
9. The method of claim 4, wherein the inert atmosphere is nitrogen, carbon dioxide, or argon.
10. The method according to claim 4, wherein the temperature of the sintering under the inert atmosphere is 400-850 ℃, and the time of the sintering under the inert atmosphere is 1-20 h.
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