CN115367723B - LiFe 2 F 6 Preparation method of coated lithium iron phosphate positive electrode material - Google Patents

LiFe 2 F 6 Preparation method of coated lithium iron phosphate positive electrode material Download PDF

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CN115367723B
CN115367723B CN202210980966.0A CN202210980966A CN115367723B CN 115367723 B CN115367723 B CN 115367723B CN 202210980966 A CN202210980966 A CN 202210980966A CN 115367723 B CN115367723 B CN 115367723B
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lithium
iron phosphate
lithium iron
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CN115367723A (en
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廖鹏
任宁
许厚军
黄赞
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Chaowei Power Group Co Ltd
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B25/00—Phosphorus; Compounds thereof
    • C01B25/16—Oxyacids of phosphorus; Salts thereof
    • C01B25/26—Phosphates
    • C01B25/45—Phosphates containing plural metal, or metal and ammonium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B02—CRUSHING, PULVERISING, OR DISINTEGRATING; PREPARATORY TREATMENT OF GRAIN FOR MILLING
    • B02C—CRUSHING, PULVERISING, OR DISINTEGRATING IN GENERAL; MILLING GRAIN
    • B02C17/00—Disintegrating by tumbling mills, i.e. mills having a container charged with the material to be disintegrated with or without special disintegrating members such as pebbles or balls
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
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    • H01M10/05—Accumulators with non-aqueous electrolyte
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    • H—ELECTRICITY
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    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
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    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
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    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • 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
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    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H—ELECTRICITY
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    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
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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
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • 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
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • 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
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    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention relates to the technical field of lithium batteries and discloses a LiFe 2 F 6 The preparation method of the coated lithium iron phosphate anode material comprises the following steps of; the method comprises the following steps: (1) Mixing iron source, phosphorus source and lithium source uniformlyCalcining the mixed material, and crushing the calcined mixed material to obtain a precursor; (2) FeF is carried out 3 Dispersing LiF and VGCF in a dispersing agent to prepare primary slurry, spraying the primary slurry on the surface of the precursor prepared in the step (1), and performing two-stage heating treatment to prepare a primary coated substrate; (3) The primary coated substrate prepared in the step (2) and FeF 2 Ball milling and heating treatment are carried out to obtain LiFe 2 F 6 Coating a lithium iron phosphate anode material; by mixing LiFe 2 F 6 The coating is coated on the surface of the lithium iron phosphate anode material, so that the electron conductivity and the ion conductivity of the lithium iron phosphate anode material are obviously increased, and the cycle performance and the electrochemical performance of the lithium battery are obviously improved.

Description

LiFe 2 F 6 Preparation method of coated lithium iron phosphate positive electrode material
Technical Field
The invention relates to the technical field of lithium batteries, in particular to a LiFe 2 F 6 A preparation method of a coated lithium iron phosphate anode material.
Background
The positive electrode material of the lithium battery currently takes ternary materials of lithium cobaltate, nickel cobalt manganese and lithium iron phosphate as main raw materials, wherein the lithium iron phosphate has the characteristics of high safety and high cycle performance, but the low electronic conductivity and the low ion conductivity enable the theoretical gram capacity of the lithium iron phosphate to be only 170mAh/g, so that the application volume of the lithium iron phosphate in a high-capacity battery is larger, and the portability is low. Therefore, in order to solve the above problems, a surface coating method is generally used in the prior art to prepare a lithium iron phosphate positive electrode material.
The preparation method of the aluminum oxide coated lithium iron phosphate anode material comprises the following steps of: mixing a lithium source, an iron source and a phosphorus source, adding the mixture into water, performing wet ball milling for one time to obtain slurry, and calcining to obtain a lithium iron phosphate semi-finished product; placing a lithium iron phosphate precursor into a mixed solution of aluminum nitrate, urea and polyethylene glycol, and rapidly stirring; carrying out hydrothermal treatment on the dispersion liquid to form sol and washing the sol with deionized water; freeze drying and high temperature calcining; then purging and heating in a mixed atmosphere of nitrogen and argon, keeping the temperature for a period of time, and then cooling in an argon atmosphere to obtain the aluminum oxide coated lithium iron phosphate anode material. The invention has the advantages of excellent energy density, cycle performance, rate discharge and other performances, low cost and high cost performance.
Further, as disclosed in publication number CN112897491a, a preparation method and application of a lithium iron phosphate positive electrode material are disclosed, comprising the following steps: (1) Mixing and refining an iron source, a phosphorus source, a lithium source, a carbon source and an additive in a dry way to obtain a mixed material; (2) Sintering the mixed material for the first time, and then crushing to obtain a crushed material; (3) And (3) sintering the crushed material for the second time, introducing a vaporizable organic carbon source during the second sintering, and then cooling to obtain the lithium iron phosphate anode material. According to the invention, the raw materials are subjected to one-step mixing and refining by using high-efficiency mixing equipment, sintered and crushed, and secondary sintering is performed to supplement carbon cladding by using a vaporizable organic carbon source, so that the product has better carbon cladding layer and particle morphology, and the obtained product has better performance, and compared with the product of the same type in the market, the product has greatly improved performance and good cycle stability, and can meet the general requirements of a high-performance lithium iron phosphate battery.
Al is commonly adopted in the prior art 2 O 3 As a surface coating material of lithium iron phosphate, but Al 2 O 3 Has no conducting capability to lithium ion, and Al 2 O 3 The impedance of the battery core can be increased, the electrochemical performance of lithium iron phosphate is not obviously improved, meanwhile, al2O3 is converted into Al-O-F after long-time circulation, the Al-O-F is difficult to resist corrosion of HF in long-time circulation as an intermediate product, and the circulation performance is not high.
Disclosure of Invention
The application provides a LiFe for solving the problems of low cycling performance and low electrochemical performance improvement effect of the coated lithium iron phosphate in the prior art 2 F 6 Preparation method of coated lithium iron phosphate anode material comprises mixing LiFe 2 F 6 The electrolyte is coated on the surface of the lithium iron phosphate anode material, so that the corrosion of the electrolyte to the material is reduced, the electron conductivity and the ion conductivity of the lithium iron phosphate anode material are increased, and the cycle performance and the electrochemical performance of the battery are obviously improved.
The specific technical scheme of the invention is as follows:
LiFe 2 F 6 The preparation method of the coated lithium iron phosphate anode material comprises the following steps:
(1) Uniformly mixing an iron source, a phosphorus source and a lithium source to prepare a mixed material, calcining the mixed material, and crushing the calcined mixed material to prepare a precursor;
(2) FeF is carried out 3 Dispersing LiF and VGCF in a dispersing agent to prepare primary slurry, spraying the primary slurry on the surface of the precursor prepared in the step (1), and performing two-stage heating treatment to prepare a primary coated substrate;
(3) The primary coated substrate prepared in the step (2) and FeF 2 Ball milling and heating treatment are carried out to obtain LiFe 2 F 6 And coating a lithium iron phosphate positive electrode material.
The application provides a preparation method of a surface coating type ternary positive electrode material, which comprises the steps of preparing a lithium iron phosphate precursor, coating a substrate for the first time and coating the substrate for the second time, and firstly using a dispersing agent to carry out FeF (iron phosphate) reaction 3 Coating LiF and VGCF on the surface of the substrate to obtain a primary coated substrate, and then coating the primary coated substrate and FeF 2 Ball milling and heating, wherein in the primary coating process, the dispersant forms carbon residue in the primary heating process, and the main components in the coating layer at the moment are organic carbon residue and FeF 3 The lithium iron phosphate is coated with a compact shell with micropores, liF and VGCF, impurities in the lithium iron phosphate substrate are removed in a high-temperature state after two-stage heating treatment, and organic carbon residues in the shell of the coating are completely converted into microporous carbon.
The present application does not directly address LiFe 2 F 6 Cladding is on the surface of substrate, need control the coating thickness on substrate surface when cladding, consequently need ball-milling to the ternary material substrate that finishes cladding according to coating thickness after cladding, can adopt other harder polishing material ternary materials to polish in ball-milling process generally, in this process, will introduce impurity into ternary positive electrode material, consequently this application has adopted the mode of secondary cladding to cladding ternary material substrate, uses FeF 2 For FeF 3 FeF when impact heating is performed with LiF 3 And LiF will first form an ordered triple rutile configuration, then in FeF 2 Under the continuous impact of Fe 2+ Will occupy a part of Fe in the triple rutile 3+ Position, form Fe 2+ And Fe (Fe) 3+ Mixed LiFe 2 F 6 In the process of coating, feF3, liF and VGCF are coated for one time, and then FeF is used 2 The primary coating material is subjected to impact thermal reaction to carry out secondary coating, and LiFe is prepared in the secondary coating process 2 F 6 The ball milling process is also carried out at the same time to prepare LiFe 2 F 6 Can control LiFe at the same time 2 F 6 The method can not introduce other impurities, and the product quality is high.
LiFe is used in the present application 2 F 6 As a coating layer of the lithium iron phosphate anode material, the cycle performance and the electrochemical performance of the anode material are obviously improved; liFe 2 F 6 Is a triple rutile structure, has the capability of removing and inserting lithium ions, has the theoretical capacity of 237mAh/g, can obviously improve the conduction effect and the electronic conductivity of lithium ions after being coated on the surface of a high-nickel ternary material substrate, obviously improves the electrochemical performance of a lithium battery, and simultaneously has the advantages of high energy consumption, low cost and low cost 2 F 6 The triple rutile structure of the lithium ion battery is not changed after lithium removal, so that the corrosion of electrolyte to a lithium iron phosphate substrate can be effectively isolated, and the cycle performance of the lithium ion battery is remarkably improved.
Preferably, the lithium source in the step (1) is one or more selected from lithium carbonate, lithium dihydrogen phosphate, lithium oxalate and lithium hydroxide.
Preferably, the phosphorus source in the step (1) is selected from one or more of ammonium dihydrogen phosphate, phosphoric acid and lithium dihydrogen phosphate.
Preferably, the iron source in the step (1) is selected from one or more of elemental iron and ferric salts.
Preferably, the calcination temperature in the step (1) is 300-400 ℃ and the calcination time is 2-3 h.
Preferably, the two-stage heating process conditions in the step (2) are as follows: the first-stage heating is carried out at a heating rate of 3 ℃/min to 300-500 ℃, the temperature is kept for 2-4 h, the second-stage heating is carried out at a heating rate of 5 ℃/min to 800-1000 ℃, and the temperature is kept for 3-7 h.
Preferably, feF in the step (3) 3 The mass part ratio of LiF, VGCF and the dispersing agent is 5-10: 8-16: 2-5: 6-12, wherein the dispersing agent is carboxymethyl cellulose.
Preferably, the ball milling rotation speed in the step (3) is 200-500 rpm, the ball milling time is 12h, and the heating temperature is 150 ℃.
Preferably, liFe in the step (3) 2 F 6 The lithium iron phosphate coated positive electrode material comprises a core layer and a coating layer coated on the outer side of the core layer, wherein the mass ratio of the coating layer to the core layer is 0.01-0.05:1, and the coating layer comprises C and LiFe 2 F 6 。
Preferably, C and LiFe in the coating 2 F 6 The mass ratio of (3-5): 1.
compared with the prior art, the application has the following technical effects:
(1) By mixing LiFe 2 F 6 The coating is coated on the surface of the lithium iron phosphate anode material, so that the corrosion of electrolyte to the material can be resisted, the electron conductivity and the ion conductivity of the lithium iron phosphate anode material can be obviously increased, and the cycle performance and the electrochemical performance of the battery are obviously improved;
(2) The application adopts a secondary coating mode during coating, and FeF is firstly coated 3 Coating LiF and VGCF once, and then using FeF 2 The primary coating material is subjected to impact thermal reaction to carry out secondary coating, and in the secondary coating process, liFe is obtained 2 F 6 Ball milling is also carried out to prepare LiFe 2 F 6 Can control LiFe at the same time 2 F 6 The coating thickness of the steel plate is obviously improved.
Detailed Description
The invention is further described below with reference to examples.
Example 1:
(1) Lithium is added according to the molar ratio: iron: phosphorus=1: 1: adding lithium carbonate, iron powder and lithium dihydrogen phosphate into a mixer to prepare a mixed material, calcining the mixed material at 400 ℃ for 3 hours, cooling along with a furnace, crushing and screening to obtain a precursor;
(2) The weight portion ratio is 10:15:4:9 FeF 3 (Alfa, 97%), liF (aladin, 99.99%), VGCF (vacuum oven drying at 60 ℃) are dispersed in carboxymethyl cellulose aqueous solution (0.005%) to prepare primary slurry, the primary slurry is sprayed on the surface of the precursor prepared in the step (1) and subjected to two-stage heating treatment to prepare primary coated base material, the primary heating is carried out at a heating rate of 3 ℃/min to 500 ℃, the heat is preserved for 2-4 h, the secondary heating is carried out at a heating rate of 5 ℃/min to 1000 ℃, and the heat is preserved for 7h;
(3) Using a ball mill to mix the primary coated substrate prepared in step (2) with FeF 2 Performing ball milling heating treatment, cleaning a stainless steel ball before using a ball milling tank, drying at 120 ℃, performing ball milling at 500rpm, performing ball milling for 12 hours at 150 ℃, performing ball milling, and sieving to obtain coated LiFe 2 F 6 Lithium iron phosphate positive electrode material.
Example 2:
(1) Lithium is added according to the molar ratio: iron: phosphorus=1: 1: adding lithium oxalate, ferric phosphate and diammonium hydrogen phosphate into a mixer to prepare a mixed material, calcining the mixed material at the calcining temperature of 300-400 ℃ for 2-3 hours, cooling along with a furnace, crushing and screening to obtain a precursor;
(2) The weight portion ratio is 10:15:4:9 FeF 3 (Alfa, 97%), liF (aladin, 99.99%), VGCF (vacuum oven drying at 60 ℃) are dispersed in carboxymethyl cellulose aqueous solution (0.005%) to prepare primary slurry, the primary slurry is sprayed on the surface of the precursor prepared in the step (1) and subjected to two-stage heating treatment to prepare a primary coated substrate, the primary heating is carried out at a heating rate of 3 ℃/min to 500 ℃, the heat is preserved for 4 hours, the secondary heating is carried out at a heating rate of 5 ℃/min to 1000 ℃, and the heat is preserved for 3-7 hours;
(3) Using a ball mill to mix the primary coated substrate prepared in step (2) with FeF 2 Performing ball milling heating treatment, cleaning with stainless steel ball before using the ball milling tank, and drying at 120deg.CThe ball milling rotating speed is 500rpm, the ball milling time is 12 hours, the heating temperature is 150 ℃, and the coated LiFe is prepared after sieving after ball milling 2 F 6 Lithium iron phosphate positive electrode material.
Example 3:
(1) Lithium is added according to the molar ratio: iron: phosphorus=1: 1: adding lithium hydroxide, ferric phosphate and lithium dihydrogen phosphate into a mixer to prepare a mixed material, calcining the mixed material at 300-400 ℃ for 2-3 hours, cooling along with a furnace, crushing and screening to obtain a precursor;
(2) The weight portion ratio is 10:15:4:9 FeF 3 (Alfa, 97%), liF (aladin, 99.99%), VGCF (vacuum oven drying at 60 ℃) are dispersed in carboxymethyl cellulose aqueous solution (0.005%) to prepare primary slurry, the primary slurry is sprayed on the surface of the precursor prepared in the step (1) and subjected to two-stage heating treatment to prepare primary coated base material, the primary heating is carried out at a heating rate of 3 ℃/min to 500 ℃, the heat is preserved for 4 hours, the secondary heating is carried out at a heating rate of 5 ℃/min to 1000 ℃, and the heat is preserved for 7 hours;
(3) Using a ball mill to mix the primary coated substrate prepared in step (2) with FeF 2 Performing ball milling heating treatment, cleaning a stainless steel ball before using a ball milling tank, drying at 120 ℃, performing ball milling at 500rpm, performing ball milling for 12 hours at 150 ℃, performing ball milling, and sieving to obtain coated LiFe 2 F 6 Lithium iron phosphate positive electrode material.
Example 4:
(1) Lithium is added according to the molar ratio: iron: phosphorus=1: 1: adding ferric oxide and lithium dihydrogen phosphate into a mixer to prepare a mixed material, calcining the mixed material at 300-400 ℃ for 2-3 hours, cooling along with a furnace, crushing and screening to obtain a precursor;
(2) The weight portion ratio is 10:15:4:9 FeF 3 (Alfa, 97%), liF (Aladin, 99.99%), VGCF (vacuum oven drying at 60deg.C) were dispersed in an aqueous carboxymethyl cellulose solution (0.005%) to prepare a primary slurry, and the primary slurry was sprayed on the slurry in step (1)Performing secondary heating treatment on the surface of the precursor of the substrate to prepare a primary coated substrate, wherein the primary heating is performed at a heating rate of 3 ℃/min to 500 ℃, the temperature is kept for 4 hours, and the secondary heating is performed at a heating rate of 5 ℃/min to 1000 ℃, and the temperature is kept for 7 hours;
(3) Using a ball mill to mix the primary coated substrate prepared in step (2) with FeF 2 Performing ball milling heating treatment, cleaning a stainless steel ball before using a ball milling tank, drying at 120 ℃, performing ball milling at 500rpm, performing ball milling for 12 hours at 150 ℃, performing ball milling, and sieving to obtain coated LiFe 2 F 6 Lithium iron phosphate positive electrode material. The method comprises the steps of carrying out a first treatment on the surface of the
Comparative example 1: (substrate surface has no coating layer)
Comparative example 1 compares with example 1: without step (3) and step (4), the other conditions were the same as in example 1.
Comparative example 2: (use of LiFe) 2 F 6 Coating
Comparative example 2 compares with example 1: direct use of LiFe in step (3) 2 F 6 Coating a substrate, wherein the substrate is coated with the following components in parts by mass: 4:9 LiFe 2 F 6 Mixing VGCF (60 ℃ vacuum oven drying) and CMC water solution (0.005%) to obtain slurry, spraying the slurry on the surface of the substrate obtained in step (2), and heating to obtain LiFe 2 F 6 Coating the substrate, wherein the heating treatment temperature is 400 ℃, and the heating time is 4 hours; for LiFe 2 F 6 Carrying out ball milling treatment on the coated substrate, wherein zirconium oxide is adopted in the ball milling process, the ball milling rotating speed is 1200rpm, and the ball milling time is 24 hours; the other conditions were the same as in example 1.
Comparative example 3: (the coating layer is Al 2 O 3 ）
Comparative example 3 compares with example 1: the coating layer is Al 2 O 3 The coating step is as follows:
(1) Lithium is added according to the molar ratio: iron: phosphorus=1: 1: adding lithium carbonate, iron powder and lithium dihydrogen phosphate into a mixer to prepare a mixed material, calcining the mixed material at 300-400 ℃ for 2-3 hours, cooling with a furnace, crushing and screening to obtain a precursor;
(2) The weight portion ratio is 100:5:3:10 mixing and stirring the precursor, aluminum nitrate, urea and polyethylene glycol in the step (1) for 3 hours to form a dispersion liquid, heating the dispersion liquid to 120 ℃, reacting for 12 hours, washing 3 times by deionized water after the reaction is finished, centrifugally collecting a precipitate, drying the precipitate in an argon atmosphere at 500 ℃ for 12 hours, and heating to 800 ℃ for 3 hours to obtain Al 2 O 3 And coating a lithium iron phosphate positive electrode material.
The lithium iron phosphate positive electrode materials prepared in examples 1-4 and comparative examples 1-3 are prepared into lithium batteries, and the preparation steps comprise: fully dry-grinding the positive electrode material, the conductive agent and the adhesive in an agate mortar for about 10min, and adding NMP for wet-grinding for 10min to obtain uniform-texture slurry, wherein the positive electrode material is prepared by the following steps: conductive agent: binder = 90:6:4, a step of; spreading aluminum foil (thickness of 0.016 mm) on a casting machine, cleaning and fixing with alcohol, and coating slurry on the aluminum foil to form a pole piece with a film scraper (0.022 mm); vacuumizing and baking the coated pole piece in a vacuum box at 120 ℃ for 6 hours; cutting the pole piece into a circular piece with the diameter of 14mm by a cutting machine to prepare a battery positive plate; and assembling the battery positive plate, the lithium plate negative electrode, the 2025 type battery shell, the polypropylene microporous diaphragm and the ethylene carbonate-diethyl carbonate-lithium hexafluorophosphate electrolyte into a lithium battery.
And testing the electrochemical performance of the positive electrode material by adopting a blue electric battery testing system: testing the first charge and discharge of the battery under the 0.1C multiplying power in a constant temperature environment at 25 ℃ and testing the voltage range to be 2.0V-3.8V; cycle life test charge-discharge cycle test is carried out under 1C multiplying power, and the test voltage range is 2.0V-3.8V; the number of cycles was 500, and the results of the electrochemical performance test are shown in table 1:
TABLE 1 electrochemical Performance test results
As can be seen from the table 1,
examples 1 to 4 compared with comparative example 1, it can be seen that the substrate surface passed through LiFe 2 F 6 After coatingThe first discharge capacity is obviously increased, the discharge capacity retention rate after 500 times of 1C circulation is high, and the discharge efficiency retention rate of the uncoated substrate after 500 times of 1C circulation is obviously reduced, which shows that the surface of the substrate passes through LiFe 2 F 6 After coating, the corrosion of the electrolyte to the internal base material can be well reduced, and the cycle performance and the charge-discharge capacity of the lithium battery are obviously improved.
Comparing examples 1-4 with comparative example 2, it can be seen that the electrochemical performance of the lithium battery is better than that of the lithium battery directly using LiFe 2 F 6 The coated substrate is better, which indicates that the anode material prepared by the secondary coating method provided by the application has better quality.
Examples 1 to 4 compared with comparative example 3, the capacity retention of examples 1 to 4 after 500 cycles at 1C was significantly higher than that of comparative example 3, indicating the use of LiFe 2 F 6 Coating lithium iron phosphate and Al 2 O 3 Compared with the coated lithium iron phosphate, the cycling performance of the lithium iron phosphate can be improved more remarkably.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent transformation of the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (7)

1. LiFe 2 F 6 The preparation method of the coated lithium iron phosphate anode material is characterized by comprising the following steps:
(1) Uniformly mixing an iron source, a phosphorus source and a lithium source to prepare a mixed material, calcining the mixed material, and crushing the calcined mixed material to prepare a precursor;
the calcination temperature is 300-400 ℃, and the calcination time is 2-3 hours;
(2) FeF is carried out 3 Dispersing LiF and VGCF in a dispersing agent to prepare primary slurry, spraying the primary slurry on the surface of the precursor prepared in the step (1), and performing two-stage heating treatment to prepare a primary coated substrate;
the two-stage heating process conditions are as follows: the first-stage heating is carried out at a heating rate of 3 ℃/min to 300-500 ℃, the temperature is kept for 2-4 hours, the second-stage heating is carried out at a heating rate of 5 ℃/min to 800-1000 ℃, and the temperature is kept for 3-7 hours;
the FeF is 3 The mass part ratio of LiF, VGCF and the dispersing agent is 5-10: 8-16: 2-5: 6-12, wherein the dispersing agent is carboxymethyl cellulose;
(3) The primary coated substrate prepared in the step (2) and FeF 2 Ball milling and heating treatment are carried out to obtain LiFe 2 F 6 And coating a lithium iron phosphate positive electrode material.
2. A LiFe as claimed in claim 1 2 F 6 The preparation method of the coated lithium iron phosphate anode material is characterized in that the lithium source in the step (1) is one or more selected from lithium carbonate, lithium dihydrogen phosphate, lithium oxalate and lithium hydroxide.
3. A LiFe as claimed in claim 1 2 F 6 The preparation method of the coated lithium iron phosphate anode material is characterized in that the phosphorus source in the step (1) is one or more selected from ammonium dihydrogen phosphate, phosphoric acid and lithium dihydrogen phosphate.
4. A LiFe as claimed in claim 1 2 F 6 The preparation method of the coated lithium iron phosphate anode material is characterized in that the iron source in the step (1) is selected from one or more of elemental iron and ferric salt.
5. A LiFe as claimed in claim 1 2 F 6 The preparation method of the coated lithium iron phosphate cathode material is characterized in that the ball milling rotating speed in the step (3) is 200-500 rpm, the ball milling time is 12h, and the heating temperature is 150 ℃.
6. A LiFe as claimed in claim 1 2 F 6 The preparation method of the coated lithium iron phosphate positive electrode material is characterized in that the step (3) is carried out by LiFe 2 F 6 The coated lithium iron phosphate positive electrode material comprises a core layerAnd a coating layer coated on the outer side of the core layer, wherein the mass ratio of the coating layer to the core layer is 0.01-0.05:1, and the coating layer comprises C and LiFe 2 F 6 。
7. A LiFe as defined in claim 6 2 F 6 The preparation method of the coated lithium iron phosphate anode material is characterized in that the mass ratio of C to LiFe2F6 in the coating layer is 3-5: 1.
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