CN112713272A - Preparation method of modified lithium battery positive electrode material - Google Patents

Preparation method of modified lithium battery positive electrode material Download PDF

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Publication number
CN112713272A
CN112713272A CN202011501754.7A CN202011501754A CN112713272A CN 112713272 A CN112713272 A CN 112713272A CN 202011501754 A CN202011501754 A CN 202011501754A CN 112713272 A CN112713272 A CN 112713272A
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roasting
powder
lithium battery
speed
stirring
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CN112713272B (en
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吴清国
朱玉巧
汪晓俊
靳文超
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Zhejiang Jinying Wali New Energy Technology Co ltd
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Zhejiang Jinying Wali 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
    • H01M4/58—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
    • 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
    • H01M4/62—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
    • 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
    • H01M4/624—Electric conductive fillers
    • H01M4/626—Metals
    • 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
    • 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
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • 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
    • 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 preparation method of a modified lithium battery anode material, which comprises the following steps: mixing an iron source compound, a lithium source compound and a phosphorus source compound, adding deionized water, and performing ultrasonic treatment to obtain a mixed solution; adding a structure directing agent into the mixed solution, and stirring to obtain a precursor solution; separating, cleaning, filtering and drying to obtain precursor powder; crushing and refining by using a jet mill, transferring the crushed powder particles to a roasting furnace for roasting, and naturally cooling to room temperature to obtain cellular lithium iron phosphate; adding carbon powder and a titanium source into absolute ethyl alcohol; adding a reducing agent while stirring, carrying out spray drying to obtain powder, placing the obtained powder in a crucible, roasting under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body; and adding the composite coating body and the lithium iron phosphate into a high-speed mixer for mixing, and roasting to obtain the modified lithium battery anode material.

Description

Preparation method of modified lithium battery positive electrode material
Technical Field
The invention relates to the technical field of lithium battery material preparation and printing, in particular to a preparation method of a modified lithium battery anode material.
Background
The lithium ion battery has a rapid technical development, and is widely applied to the fields of electronic products, electric vehicles, hybrid electric vehicles, large-scale power grids, new energy storage devices and the like. The lithium iron phosphate material has the advantages of good safety performance, long cycle life, rich resources, environmental friendliness and the like, is recognized as the most promising lithium ion power and energy storage battery anode material by the international power supply world, has important significance for the development of the printing industry and the novel energy storage industry, and has huge market prospect and social significance. However, the structural characteristics of the lithium iron phosphate with the olivine structure determine that lithium ions can only conduct along one dimension in the direction in the charging and discharging process, thereby resulting in lower electronic conductivity; the poor conductivity and the slow diffusion rate of lithium ions are the major difficulties restricting the development of the lithium iron phosphate power battery industry.
The most common methods to solve this problem are surface carbon coating techniques and metal ion doping. Although carbon coating can improve the battery performance of lithium iron phosphate to a certain extent, carbon coating has more difficulties and challenges in practical production. For example, when the carbon content is low, a complete and uniform coating layer cannot be formed on the surface of lithium iron phosphate, and sufficient conductivity cannot be obtained; as the carbon content increases, the coating layer thickens, not only reducing the tap density of the active material but also blocking the diffusion path of lithium ions. The metal ions are doped by adding LiFePO4A small amount of impurity metal ions are doped in the material, so that the local energy of crystal lattices is changed, vacancy defects are generated, and the electronic conductivity of the material is obviously improved; however, the modification method still has the defects that doping transition group elements can improve the bulk electronic conductivity of the material, but has small influence on the size of the material, and the lithium ion diffusion rate of the material is not easy to improve, so that the electrochemical performance improvement effect on the material is limited.
Disclosure of Invention
Aiming at the defects of the modification method of the lithium iron phosphate positive electrode material in the prior art, the invention provides the preparation method of the composite lithium iron phosphate, and the method leads the lithium iron phosphate to be changed into a honeycomb shape from an olive shape by introducing the structure directing agent, shortens and unblocks an ion channel, and improves the diffusion rate of lithium ions; and the carbon/titanium compound is coated outside the lithium iron phosphate to form lattice defects, allow ions to pass through freely, improve the electronic conductivity and have good tap density, thereby obviously improving the electrochemical performance of the lithium battery anode material on the whole.
In order to achieve the purpose, the invention adopts the technical scheme that:
a preparation method of a modified lithium battery positive electrode material comprises the following steps:
s1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, adding deionized water, and carrying out ultrasonic treatment until the mixture is fully mixed to obtain a mixed solution;
s2: adding a structure directing agent into the mixed solution obtained in the step S1, and continuously stirring to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and then cleaning, filtering and drying the precursor solution by using deionized water to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, transferring the crushed powder particles to a roasting furnace for roasting, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding carbon powder and a titanium source into absolute ethyl alcohol; then adding a reducing agent while stirring, carrying out spray drying to obtain powder, placing the obtained powder in a crucible, roasting under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body;
s6: and adding the composite coating body and the lithium iron phosphate into a high-speed mixer for mixing, and roasting to obtain the modified lithium iron phosphate anode material.
Furthermore, in the step S1, the atomic percentages of the lithium, the iron and the phosphorus are (1-1.2): 0.96-1.2):1, and the solid-to-liquid ratio of the mixture of the three to the deionized water is 1g (5-10) ml; the temperature of ultrasonic treatment is 15-25 ℃, and the time is 20-40 min; in the step S2, the structure directing agent is any one or more of polyvinyl alcohol (PVA), polyethylene glycol (PEG) and polymethyl methacrylate (PMMA), and accounts for 3-8% of the total amount of the mixed solution obtained in the step S1; the stirring speed is 10000-30000rpm, and the stirring time is 60-120 min.
Furthermore, the atomic percentage of the lithium, the iron and the phosphorus is 1.15:1.05:1, and the solid-to-liquid ratio of the mixture of the lithium, the iron and the phosphorus to the deionized water is 1g:8 ml; the temperature of ultrasonic treatment is 20 ℃, and the time is 35 min; the structure directing agent accounts for 5% of the total amount of the mixed solution obtained in the step S1; the stirring speed was 24000rpm, and stirring was performed for 90 min.
Furthermore, in step S3, the centrifugal rotation speed is controlled to be 1500-; in step S4, the gas pressure of the jet mill is 0.7-1.0MPa, the rotation frequency of the grading wheel is 30-50Hz, and the feeding speed is 100-200 g/S; the roasting process is to raise the temperature to 600-1000 ℃ at the heating rate of 3-5 ℃/h and keep the temperature for 1-5 h.
Furthermore, the centrifugal rotating speed is 2500 r/min; the gas pressure of the jet mill is 0.85MPa, the rotation frequency of the grading wheel is 45Hz, and the feeding speed is 165 g/s; the roasting process is to heat to 850 ℃ at the heating rate of 3.5 ℃/h and keep the temperature for 3 h.
Furthermore, in the step S5, the titanium source is titanium dioxide, and the mass ratio of the titanium source to the carbon powder is 1 (5-9); the stirring speed is 8000-; the reducing agent is glycol, and the using amount of the reducing agent is 2-4% of the mass of the titanium source and the carbon powder; the roasting process is roasting for 3-8h at the temperature of 350-550 ℃.
Furthermore, the titanium source is titanium dioxide, and the mass ratio of the titanium source to the carbon powder is 1: 7; stirring speed 15000 rpm; the dosage of the reducing agent is 3 percent of the mass of the titanium source and the carbon powder; the roasting process is roasting for 4.5 hours at 500 ℃.
Furthermore, in the step S6, the mass ratio of the composite coating to the lithium iron phosphate is (1-3): 15; the stirring speed is 30000 and 50000 rpm; the roasting process is roasting for 4-8h at the temperature of 550-850 ℃, and cooling to room temperature in the furnace.
Furthermore, the mass ratio of the composite coating to the lithium iron phosphate is 2.5: 15; the stirring speed is 35000 rpm; the roasting process is roasting for 5.5 hours at 750 ℃.
Has the advantages that:
1. the preparation method of the lithium battery anode material adopts a hydrothermal synthesis method, adds a high molecular polymer as a structure directing agent into a mixed solution of an iron source, a lithium source and a phosphorus source compound, removes a structure directing template through high-temperature roasting, finally obtains cellular lithium iron phosphate, shortens and unblocks an ion channel by forming a cellular result, enables ions to rapidly and freely pass through, and improves the diffusion rate of the lithium ions.
2. Before the process of roasting lithium iron phosphate, the precursor powder is crushed and refined by adopting the jet mill, and the micron-sized lithium iron phosphate is formed by controlling the relevant parameters of the jet mill, so that the lithium ion diffusion rate is increased, and the tap density is better.
3. The composite coating body is formed by reducing and roasting the carbon powder and the titanium source, compared with the existing carbon powder, titanium ions are filled in pores of the carbon structure, and the composite coating body has high tap density and good electronic conductivity; the electronic conductivity is not required to be improved by improving the carbon content, and the problem that the lithium ion diffusion channel is blocked due to the reduction of the tap density of the active substance because the carbon layer is too thick is also avoided.
4. The honeycomb-shaped lithium iron phosphate and the composite coating body are added into a high-speed mixer to be fully mixed and roasted, and the process is controlled to enable the composite coating body to form a complete and uniform coating layer on the surface of the lithium iron phosphate, so that the modified lithium iron phosphate has good electronic conductivity and high tap density, is beneficial to miniaturization of a high-capacity lithium battery, has good cycle performance and stable performance, remarkably improves the electrochemical performance of a lithium iron phosphate anode material, and lays a foundation for further application.
Detailed Description
The present invention is further illustrated below by reference to the following examples, which are intended to be illustrative of the invention only and are not intended to be limiting.
Example 1
S1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, and adding deionized water, wherein the atomic percentage of lithium, iron and phosphorus is 1:0.96:1, and the solid-to-liquid ratio of the mixture of the iron source compound, the lithium source compound and the phosphorus source compound to the deionized water is 1g:5 ml; then carrying out ultrasonic treatment at the temperature of 15 ℃ for 20min to obtain a mixed solution;
s2: adding a polyvinyl alcohol (PVA) structure directing agent into the mixed solution, wherein the structure directing agent accounts for 3% of the total amount of the mixed solution; continuously stirring at the speed of 10000rpm for 60min to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and controlling the centrifugal rotation speed to be 1500 r/min; then washing with deionized water, filtering and drying to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, controlling the gas pressure of the jet mill to be 0.7MPa, the rotating frequency of a grading wheel to be 30Hz, and the feeding speed to be 100 g/s; transferring the crushed powder particles to a roasting furnace for roasting, heating to 600 ℃ at a heating rate of 3 ℃/h, preserving heat for 1h, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding titanium dioxide and carbon powder in a mass ratio of 1:5 into absolute ethyl alcohol; then adding reducing agent ethylene glycol while stirring at the speed of 8000rpm, wherein the dosage of the reducing agent ethylene glycol is 2 percent of the total mass of the titanium dioxide and the carbon powder; spray drying to obtain powder, placing the powder in a crucible, roasting for 3h under the condition of raising the temperature to 350 ℃ at 1 ℃/min under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body;
s6: adding the composite coating and the lithium iron phosphate in a mass ratio of 1:15 into a high-speed mixer, stirring at a speed of 30000rpm for 30min, heating to 350 ℃ at a speed of 2 ℃/min, keeping the temperature for 30min, heating to 550 ℃ at a speed of 3 ℃/min, and roasting for 4h to obtain the modified lithium battery cathode material.
Example 2
S1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, and adding deionized water, wherein the atomic percentage of lithium, iron and phosphorus is 1:1.2:1, and the solid-to-liquid ratio of the mixture of the iron source compound, the lithium source compound and the phosphorus source compound to the deionized water is 1g:10 ml; then carrying out ultrasonic treatment for 40min at the temperature of 25 ℃ to obtain a mixed solution;
s2: adding a structure-directing agent polyethylene glycol (PEG) into the mixed solution, wherein the structure-directing agent accounts for 8% of the total amount of the mixed solution; continuously stirring at the speed of 30000rpm for 120min to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and controlling the centrifugal rotation speed to be 3000 r/min; then washing with deionized water, filtering and drying to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, controlling the gas pressure of the jet mill to be 1.0MPa, the rotating frequency of a grading wheel to be 50Hz, and the feeding speed to be 200 g/s; transferring the crushed powder particles to a roasting furnace for roasting, heating to 1000 ℃ at a heating rate of 5 ℃/h, preserving heat for 5h, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding titanium dioxide and carbon powder in a mass ratio of 1:9 into absolute ethyl alcohol; then adding reducing agent glycol while stirring at the speed of 20000rpm, wherein the dosage of the reducing agent glycol is 4% of the total mass of titanium dioxide and carbon powder; spray drying to obtain powder, placing the powder in a crucible, roasting for 8h under the condition of raising the temperature to 550 ℃ at the speed of 5 ℃/min under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body;
s6: adding the composite coating body and the lithium iron phosphate in a mass ratio of 1:5 into a high-speed mixer, stirring at a speed of 50000rpm for 120min, heating to 350 ℃ at a speed of 1 ℃/min, keeping the temperature for 30min, heating to 850 ℃ at a speed of 5 ℃/min, and roasting for 8h to obtain the modified lithium battery cathode material.
Example 3
S1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, and adding deionized water, wherein the atomic percentage of lithium, iron and phosphorus is 1.2:1.2:1, and the solid-to-liquid ratio of the mixture of the iron source compound, the lithium source compound and the phosphorus source compound to the deionized water is 1g:8 ml; then carrying out ultrasonic treatment at the temperature of 20 ℃ for 25min to obtain a mixed solution;
s2: adding a structure directing agent polymethyl methacrylate (PMMA) into the mixed solution, wherein the structure directing agent accounts for 4% of the total amount of the mixed solution; continuously stirring at the speed of 15000rpm for 80min to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and controlling the centrifugal rotation speed to be 2000 r/min; then washing with deionized water, filtering and drying to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, controlling the gas pressure of the jet mill to be 0.85MPa, the rotating frequency of a grading wheel to be 35Hz, and the feeding speed to be 120 g/s; transferring the crushed powder particles to a roasting furnace for roasting, heating to 800 ℃ at a heating rate of 3 ℃/h, preserving heat for 1h, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding titanium dioxide and carbon powder in a mass ratio of 1:7 into absolute ethyl alcohol; then adding reducing agent ethylene glycol at the speed of 12000rpm while stirring, wherein the dosage of the reducing agent ethylene glycol is 2.5 percent of the total mass of the titanium dioxide and the carbon powder; spray drying to obtain powder, placing the powder in a crucible, heating to 400 ℃ at a speed of 1 ℃/min under the protection of inert gas, roasting for 5h, and cooling along with a furnace to obtain a composite coating body;
s6: adding the composite coating and the lithium iron phosphate in a mass ratio of 1:10 into a high-speed mixer, stirring at a speed of 35000rpm for 45min, heating to 350 ℃ at a speed of 5 ℃/min, keeping the temperature for 30min, heating to 650 ℃ at a speed of 2 ℃/min, and roasting for 5h to obtain the modified lithium battery cathode material.
Example 4
S1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, and adding deionized water, wherein the atomic percentage of lithium, iron and phosphorus is 1.1:1:1, and the solid-to-liquid ratio of the mixture of the iron source compound, the lithium source compound and the phosphorus source compound to the deionized water is 1g:8 ml; then carrying out ultrasonic treatment for 35min at the temperature of 25 ℃ to obtain a mixed solution;
s2: adding a structure directing agent polyvinyl alcohol (PVA) into the mixed solution, wherein the structure directing agent accounts for 6.5 percent of the total amount of the mixed solution; continuously stirring at 25000rpm for 100min to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and controlling the centrifugal rotation speed to be 2500 r/min; then washing with deionized water, filtering and drying to obtain precursor powder;
s4: crushing and thinning the precursor powder by using a jet mill, controlling the gas pressure of the jet mill to be 0.9MPa, the rotating frequency of a grading wheel to be 45Hz, and the feeding speed to be 180 g/s; transferring the crushed powder particles to a roasting furnace for roasting, heating to 850 ℃ at the heating rate of 5 ℃/h, preserving heat for 1h, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding titanium dioxide and carbon powder in a mass ratio of 1:8 into absolute ethyl alcohol; then, adding reducing agent ethylene glycol at the speed of 18000rpm while stirring, wherein the dosage of the reducing agent ethylene glycol is 3.5 percent of the total mass of the titanium dioxide and the carbon powder; spray drying to obtain powder, placing the powder in a crucible, roasting for 6.5h under the condition of raising the temperature to 500 ℃ at the speed of 5 ℃/min under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body;
s6: adding the composite coating and the lithium iron phosphate in a mass ratio of 1:6 into a high-speed mixer, stirring at a speed of 45000rpm for 80min, heating to 350 ℃ at a speed of 2 ℃/min, keeping the temperature for 30min, heating to 800 ℃ at a speed of 4 ℃/min, and roasting for 7h to obtain the modified lithium battery cathode material.
Example 5
S1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, and adding deionized water, wherein the atomic percentage of lithium, iron and phosphorus is 1.15:1.05:1, and the solid-to-liquid ratio of the mixture of the iron source compound, the lithium source compound and the phosphorus source compound to the deionized water is 1g:8 ml; then carrying out ultrasonic treatment for 35min at the temperature of 20 ℃ to obtain a mixed solution;
s2: adding a polyvinyl alcohol (PVA) structure directing agent into the mixed solution, wherein the structure directing agent accounts for 5% of the total amount of the mixed solution; continuously stirring at the speed of 24000rpm for 90min to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and controlling the centrifugal rotation speed to be 2500 r/min; then washing with deionized water, filtering and drying to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, wherein the gas pressure of the jet mill is controlled to be 0.85MPa, the rotating frequency of a grading wheel is 45Hz, and the feeding speed is 165 g/s; transferring the crushed powder particles to a roasting furnace for roasting, heating to 850 ℃ at the heating rate of 3.5 ℃/h, preserving heat for 1h, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding titanium dioxide and carbon powder in a mass ratio of 1:7 into absolute ethyl alcohol; then adding reducing agent ethylene glycol while stirring at the speed of 15000rpm, wherein the dosage of the reducing agent ethylene glycol is 3 percent of the total mass of the titanium dioxide and the carbon powder; spray drying to obtain powder, placing the powder in a crucible, heating to 500 deg.C at 5 deg.C/min under the protection of inert gas, calcining for 4.5h, and furnace cooling to obtain composite coating body;
s6: adding the composite coating and the lithium iron phosphate in a mass ratio of 1:6 into a high-speed mixer, stirring at a speed of 35000rpm for 30min, heating to 350 ℃ at a speed of 2 ℃/min, keeping the temperature for 40min, heating to 750 ℃ at a speed of 3 ℃/min, and roasting for 5.5h to obtain the modified lithium battery cathode material.
Comparative example:
commercially available lithium iron phosphate and the carbon powder used in the step S5 in the embodiment 5 are added into a high-speed mixer according to the mass ratio of 1:6, stirred at the speed of 35000rpm for 30min, then heated to 350 ℃ at the speed of 2 ℃/min, kept for 40min, heated to 750 ℃ at the speed of 3 ℃/min, and roasted for 5.5h to obtain the lithium battery cathode material.
Through detection, the lithium battery positive electrode materials prepared in the examples 1 to 5 and the comparative example have the following properties:
experiment of Tap density (g/cm)3) Conductivity (S/cm)
Example 1 1.7 2.94×10-2
Example 2 1.9 3.80×10-2
Example 3 2.0 3.37×10-2
Example 4 2.1 4.21×10-2
Example 5 2.3 4.35×10-2
Comparative example 1.3 2.04×10-2
The above description is only a preferred embodiment of the present invention, and the scope of the present invention is not limited to the above embodiment, but equivalent modifications or changes made by those skilled in the art according to the present disclosure should be included in the scope of the present invention as set forth in the appended claims.

Claims (10)

1. A preparation method of a modified lithium battery positive electrode material is characterized by comprising the following steps:
s1: mixing an iron source compound, a lithium source compound and a phosphorus source compound, adding deionized water, and carrying out ultrasonic treatment until the mixture is fully mixed to obtain a mixed solution;
s2: adding a structure directing agent into the mixed solution obtained in the step S1, and continuously stirring to obtain a precursor solution;
s3: centrifugally separating the precursor solution, and then cleaning, filtering and drying the precursor solution by using deionized water to obtain precursor powder;
s4: crushing and refining the precursor powder by using a jet mill, transferring the crushed powder particles to a roasting furnace for roasting, and naturally cooling to room temperature to obtain cellular lithium iron phosphate;
s5: adding carbon powder and a titanium source into absolute ethyl alcohol; then adding a reducing agent while stirring, carrying out spray drying to obtain powder, placing the obtained powder in a crucible, roasting under the protection of inert gas, and cooling along with a furnace to obtain a composite coating body;
s6: and adding the composite coating body and the lithium iron phosphate into a high-speed mixer for mixing, and roasting to obtain the modified lithium battery anode material.
2. The method as claimed in claim 1, wherein the atomic percentages of Li, Fe and P in step S1 are (1-1.2): 0.96-1.2):1, and the solid-to-liquid ratio of the mixture of Li, Fe and P to DI water is 1g (5-10) ml; the temperature of ultrasonic treatment is 15-25 ℃, and the time is 20-40 min; in the step S2, the structure directing agent is any one or more of polyvinyl alcohol (PVA), polyethylene glycol (PEG) and polymethyl methacrylate (PMMA), and accounts for 3-8% of the total amount of the mixed solution obtained in the step S1; the stirring speed is 10000-30000rpm, and the stirring time is 60-120 min.
3. The method for preparing the modified lithium battery cathode material as claimed in claim 2, wherein the atomic percentages of the lithium, the iron and the phosphorus are 1.15:1.05:1, and the solid-to-liquid ratio of the mixture of the three to deionized water is 1g:8 ml; the temperature of ultrasonic treatment is 20 ℃, and the time is 35 min; the structure directing agent accounts for 5% of the total amount of the mixed solution obtained in the step S1; the stirring speed was 24000rpm, and stirring was performed for 90 min.
4. The method as claimed in claim 1, wherein the step S3 is performed at a centrifugal speed of 1500-; in step S4, the gas pressure of the jet mill is 0.7-1.0MPa, the rotation frequency of the grading wheel is 30-50Hz, and the feeding speed is 100-200 g/S; the roasting process is to raise the temperature to 600-1000 ℃ at the heating rate of 3-5 ℃/h and keep the temperature for 1-5 h.
5. The method for preparing the modified lithium battery positive electrode material as claimed in claim 4, wherein the centrifugal rotation speed is 2500 r/min; the gas pressure of the jet mill is 0.85MPa, the rotation frequency of the grading wheel is 45Hz, and the feeding speed is 165 g/s; the roasting process is to heat to 850 ℃ at the heating rate of 3.5 ℃/h and keep the temperature for 3 h.
6. The method for preparing the modified lithium battery cathode material as claimed in claim 1, wherein the titanium source is titanium dioxide in step S5, and the mass ratio of the titanium source to the carbon powder is 1 (5-9); the stirring speed is 8000-; the reducing agent is glycol, and the using amount of the reducing agent is 2-4% of the mass of the titanium source and the carbon powder; the roasting process is roasting for 3-8h at the temperature of 350-550 ℃.
7. The preparation method of the modified lithium battery cathode material as claimed in claim 6, wherein the titanium source is titanium dioxide, and the mass ratio of the titanium source to the carbon powder is 1: 7; stirring speed 15000 rpm; the dosage of the reducing agent is 3 percent of the mass of the titanium source and the carbon powder; the roasting process is roasting for 4.5 hours at 500 ℃.
8. The method for preparing the modified lithium battery positive electrode material as claimed in claim 1, wherein the mass ratio of the composite coating to the lithium iron phosphate in step S6 is (1-3): 15; the stirring speed is 30000 and 50000 rpm; the roasting process is roasting for 4-8h at the temperature of 550-850 ℃, and cooling to room temperature in the furnace.
9. The method for preparing the modified lithium battery positive electrode material as claimed in claim 8, wherein the mass ratio of the composite coating to the lithium iron phosphate is 2.5: 15; the stirring speed is 35000 rpm; the roasting process is roasting for 5.5 hours at 750 ℃.
10. The modified lithium battery positive electrode material prepared by the preparation method according to any one of claims 1 to 9.
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