CN109216673B - Lithium iron phosphate/multilayer graphene composite material, preparation method thereof and lithium ion battery using same - Google Patents

Lithium iron phosphate/multilayer graphene composite material, preparation method thereof and lithium ion battery using same Download PDF

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CN109216673B
CN109216673B CN201810944777.1A CN201810944777A CN109216673B CN 109216673 B CN109216673 B CN 109216673B CN 201810944777 A CN201810944777 A CN 201810944777A CN 109216673 B CN109216673 B CN 109216673B
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composite material
multilayer graphene
iron phosphate
lithium iron
graphene composite
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CN109216673A (en
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徐军明
杨政鸿
宋开新
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Shanghai Yunbi Technology Co ltd
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Hangzhou Dianzi University
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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
    • H01M4/364—Composites as mixtures
    • 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
    • H01M4/58—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
    • 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
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • 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
    • 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 discloses a lithium iron phosphate/multilayer graphene composite material, a preparation method thereof and a lithium ion battery using the same, wherein the lithium iron phosphate/multilayer graphene composite material comprises the following steps: step S1, preparing an iron oxide/multilayer graphene composite material; step S2, converting the iron oxide in the iron oxide/multilayer graphene composite material into lithium iron phosphate to form the lithium iron phosphate/multilayer graphene composite material. By adopting the technical scheme of the invention, the lithium iron phosphate can be prepared on the surface of the flexible multilayer graphene, and the particle size of the lithium iron phosphate is smaller and mainly ranges from 100nm to 200nm, so that the problems that the lithium iron phosphate cannot be bent and the conductivity is poor are solved, and the method is suitable for flexible lithium ion batteries.

Description

Lithium iron phosphate/multilayer graphene composite material, preparation method thereof and lithium ion battery using same
Technical Field
The invention belongs to the technical field of materials, and particularly relates to a lithium iron phosphate/multilayer graphene composite material, a preparation method thereof and a lithium ion battery using the same.
Background
With the rapid progress of electronic technology, more and more electronic devices are developing towards the direction of lightness, thinness, flexibility and wearability, and lithium ion batteries have high energy density, good cycle performance and good stability, and are the most ideal candidates for developing flexible energy storage devices. The olivine-structured lithium iron phosphate material has the advantages of good thermal stability, long cycle life, environmental friendliness, rich raw material sources and the like, and is the most potential positive electrode material of the lithium ion battery at present. Traditional products such as lithium ion batteries are rigid, and when the products are bent and folded, the separation of electrode materials and current collectors is easily caused, so that the electrochemical performance is influenced, even short circuit is caused, and serious safety problems occur.
Reducing the size of lithium iron phosphate and loading it on a flexible substrate is a key technology for realizing flexible lithium ion batteries. Among them, the recombination with graphene is one of the hot spots of research. However, at present, graphene is always added as a conductive agent, and graphene and lithium iron phosphate are in a mixed state. Or coating the graphene on LiFePO4A surface. Only a small part of the research on loading lithium iron phosphate to graphene is carried out, but mainly a one-step synthesis method is adopted, and mainlyHigh temperature solid phase method, carbothermic method, hydrothermal method, sol-gel method, etc. However, the size uniformity and the distribution uniformity on the surface of graphene of the lithium iron phosphate synthesized by the methods are to be improved.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a lithium iron phosphate/multilayer graphene composite material, a preparation method thereof and a lithium ion battery using the same, wherein the composite material is prepared by adopting a two-step method, and uniform ferric oxide is grown on the surface of multilayer graphene in situ; and then converting the iron oxide nanoparticles loaded on the surface of the graphene into lithium iron phosphate nanoparticles, wherein the technical scheme can enable the lithium iron phosphate particles to be uniformly loaded on the surface of the multilayer graphene.
In order to solve the technical problems in the prior art, the technical scheme of the invention is as follows:
the lithium iron phosphate/multilayer graphene composite material is characterized in that lithium iron phosphate particles are loaded on the surface of multilayer graphene, wherein the lithium iron phosphate particles are formed by in-situ growth of uniform ferric oxide on the surface of the multilayer graphene and then transformation.
According to the preferable technical scheme, the particle size of the lithium iron phosphate particles is 100-200 nm.
The invention also discloses a preparation method of the lithium iron phosphate/multilayer graphene composite material, which comprises the following steps:
step S1, preparing an iron oxide/multilayer graphene composite material;
step S2, converting iron oxide in the iron oxide/multilayer graphene composite material into lithium iron phosphate to form a lithium iron phosphate/multilayer graphene composite material;
wherein the step S1 further comprises the steps of:
s10: weighing dimethyl formamide DMF and distilled water in a volume ratio of 8:2, and mixing to obtain a mixed solvent;
s11: adding expanded graphite, and performing ultrasonic oscillation to obtain a multilayer graphene suspension;
s12: adding anhydrous sodium acetate and ferrous chloride tetrahydrate into the multilayer graphene suspension, stirring at normal temperature for 5-10 minutes until the anhydrous sodium acetate and the ferrous chloride tetrahydrate are fully dissolved, then transferring the multilayer graphene suspension into a water bath kettle, stirring in a water bath at 90 ℃ for 2 hours, taking out, and then continuously stirring at room temperature for 5 minutes until cooling; taking out the reactant, and centrifugally cleaning the reactant by using alcohol and distilled water to obtain the iron oxide/multilayer graphene composite material;
the step S2 further includes the steps of:
s20: adding distilled water and lithium dihydrogen phosphate which are equal in volume to the original mixed solvent into the centrifuged iron oxide/multilayer graphene composite material, stirring at room temperature for 5 minutes until the mixture is dissolved, then transferring the mixture into a water bath kettle, stirring in a water bath at 70 ℃ for 2 hours, taking out, and drying in an oven at 70 ℃ for 24 hours;
s21: and grinding the dried composite material for half an hour, transferring the ground composite material into a tubular furnace, and calcining the composite material for 2-10 hours at 650 ℃ under the protection of a nitrogen-hydrogen atmosphere to obtain the lithium iron phosphate/multilayer graphene composite material.
Preferably, in step S11, the amount of the expanded graphite added to the mixed solvent is 2 mg/ml.
Preferably, in step S11, the ultrasonic oscillation time is 2 to 5 hours.
Preferably, in step S12, the addition amount of the ferrous chloride tetrahydrate relative to the mixed solvent is 8-12 mg/ml, and the addition amount of the anhydrous sodium acetate relative to the mixed solvent is 20 mg/ml.
As a preferable technical solution, in step S20, the addition amount of lithium dihydrogen phosphate is determined by the addition amount of ferrous chloride tetrahydrate in step S12, wherein the molar ratio of Li ions to Fe ions is 1: 1.15.
preferably, in step S21, under the protection of nitrogen-hydrogen mixed gas (nitrogen 95%, hydrogen 5%), heating to 650 ℃ at a rate of 3 ℃/min and maintaining for 2-10 h.
As a preferred technical scheme, the lithium iron phosphate is uniformly distributed on the surface of the graphene, wherein the particle size of lithium iron phosphate particles is mainly distributed between 100nm and 200 nm.
The invention also discloses a lithium ion battery, and the anode material of the lithium ion battery adopts the lithium iron phosphate/multilayer graphene composite material of claims 1 to 3 or the lithium iron phosphate/multilayer graphene composite material prepared by the method of claims 4 to 9.
Compared with the prior art, the invention has the following beneficial effects:
(1) the existing preparation method of compounding lithium iron phosphate and graphene is to add iron ions, lithium ions and phosphate ions together by a one-step method and then synthesize a precursor by chemical codeposition. The precursor distribution of the method is difficult to be uniformly distributed on the surface of the graphene, so that the final lithium iron phosphate is not uniformly distributed. The two-step method adopted by the invention is to prepare the iron oxide nanoparticles on the surface of the multilayer graphene, the iron oxide is uniformly distributed and has small particles, and the deposition of the iron oxide on the surface of the graphene is easy to control. And then, phosphate ions and lithium ions are adsorbed on the surface of the iron oxide, so that uniformly distributed lithium iron phosphate particles can be obtained, the size of the main particles is 100-200 nm, and gaps are formed among the lithium iron phosphate particles, so that the original appearance can be maintained when the multilayer graphene deforms.
(2) The lithium iron phosphate/multilayer graphene prepared by the method is loaded on the surface of the multilayer graphene, the multilayer graphene provides a good support substrate for the lithium iron phosphate, and the problem of low electronic conductivity of the lithium iron phosphate is solved. The multilayer graphene has the advantages of simple preparation process, good conductivity, large specific surface area and strong metal ion loading capacity.
(3) The method has simple overall process, easy control and convenient production.
Description of the drawings:
fig. 1 is a flow chart illustrating steps of a method for preparing a lithium iron phosphate/multilayer graphene composite material according to the present invention;
fig. 2 is a high power scanning electron microscope image of a lithium iron phosphate/multilayer graphene composite material of instantiation 4 of the present invention;
fig. 3 is an XRD pattern of the composite material of lithium iron phosphate/multilayer graphene of instantiation 4 of the present invention;
fig. 4 is a graph illustrating a first charge and discharge curve of the lithium iron phosphate/multilayer graphene composite material of instantiation 4 of the present invention at a charge and discharge current of 0.1C (17 mAh/g);
fig. 5 is a specific capacitance performance diagram of the lithium iron phosphate/multilayer graphene composite material of instantiation 4 of the present invention at different rates (0.1C,0.5C,1C,2C,5C,10C,0.1C, based on a lithium iron phosphate theoretical capacity of 170 mAh/g) of charge and discharge currents;
fig. 6 is a graph of the cycle performance of the lithium iron phosphate/multilayer graphene composite material of instantiation 3 of the present invention at a charge and discharge current of 0.5C (85 mAh/g).
Detailed Description
In order to better explain the process and scheme of the present invention, the following invention is further described with reference to the accompanying drawings and examples. The specific embodiments described herein are merely illustrative of the invention and do not delimit the invention.
In the prior art, a preparation method of compounding lithium iron phosphate and graphene is to add iron ions, lithium ions and phosphate ions together by a one-step method, and then synthesize a precursor by chemical codeposition. The precursor distribution of the method is difficult to be uniformly distributed on the surface of the graphene, so that the final lithium iron phosphate is not uniformly distributed.
In order to solve the technical problem, the invention discloses a preparation method of a lithium iron phosphate/multilayer graphene composite material, which comprises the following steps:
step S1, preparing an iron oxide/multilayer graphene composite material;
step S2, converting iron oxide in the iron oxide/multilayer graphene composite material into lithium iron phosphate to form the lithium iron phosphate/multilayer graphene composite material;
wherein, the step S1 further includes the following steps:
s10: measuring DMF and distilled water with a volume ratio of 8:2, mixing the DMF and the distilled water to obtain a mixed solvent, and calculating the volume sum of the DMF and the distilled water as the volume of the mixed solution;
s11: adding expanded graphite, and performing ultrasonic oscillation for 2 hours to obtain a multilayer graphene mixed solution;
s12: ferrous chloride tetrahydrate and anhydrous sodium acetate are added into the multilayer graphene mixed solution. The addition amount of anhydrous sodium acetate is 20mg/ml, the addition amount of ferrous chloride tetrahydrate is 8-12 mg/ml, the solution is stirred for 10 minutes at room temperature until the solution is fully dissolved, then the solution is transferred to a water bath kettle to be stirred for 2 hours in a water bath at 90 ℃, the solution is taken out and is continuously stirred for 5 minutes at room temperature until the solution is cooled, and the iron oxide/multilayer graphene composite material is obtained.
Step S2 further includes the steps of:
s20: taking out reactants, centrifugally cleaning the reactants for 3 times respectively by using alcohol and distilled water, adding a proper amount of distilled water after cleaning to form an iron oxide/multilayer graphene suspension, and adding lithium dihydrogen phosphate, wherein the molar ratio of the lithium dihydrogen phosphate to ferrous chloride tetrahydrate in S12 is 1: 1.15, stirring the mixture at room temperature for 5 minutes until the mixture is dissolved, then transferring the mixture into a water bath kettle to be stirred in a water bath at 70 ℃ for 2 hours, taking out the mixture, and drying the mixture in an oven at 70 ℃ for 24 hours;
s21: and grinding the dried composite material for half an hour, transferring the ground composite material into a tubular furnace, heating the ground composite material to 650 ℃ at the speed of 3 ℃/min under the protection of a nitrogen-hydrogen atmosphere, and calcining the ground composite material for 2 to 10 hours to obtain the lithium iron phosphate/multilayer graphene composite material.
In the technical scheme, uniform ferric oxide is grown in situ on the surface of the multilayer graphene; and then converting the iron oxide nanoparticles loaded on the surface of the graphene into lithium iron phosphate nanoparticles, wherein the lithium iron phosphate/multilayer graphene composite material prepared by the method can enable the lithium iron phosphate particles to be uniformly loaded on the surface of the multilayer graphene.
EXAMPLE 1
Mixing 8ml of DMF (dimethyl formamide) with 2ml of distilled water to serve as a mixed solvent, adding 20mg of expanded graphite, carrying out ultrasonic oscillation for 3 hours to obtain a required multilayer graphene solution, and adding 200mg of CH (carbon-hydrogen) into the mixed solution3COONa and 80mg FeCl2·4H2O, magnetically stirring for 10 minutes. Then transferred to a water bath kettle, and stirred for 2 hours in a water bath at the temperature of 90 ℃ and the rotating speed of 320 r/min. Taking out reactants, respectively centrifuging 3 times by using alcohol and distilled water to obtain an iron oxide/multilayer graphene composite material, then adding 10ml of distilled water and 36mg of lithium dihydrogen phosphate crystals, stirring for 5 minutes at normal temperature until the lithium dihydrogen phosphate crystals are dissolved, transferring to a water bath kettle, stirring in water bath at the rotating speed of 320r/min at 70 ℃ for 2 hours, after that, placing in a 70 ℃ drying oven for drying for 24 hours, grinding the dried product for half an hour, transferring to a tubular furnace, and under the protection of nitrogen and hydrogen atmosphere, performing centrifugation at 3 ℃/m for 3 times to obtain an iron oxide/multilayer graphene composite materialAnd heating to 650 ℃ at the in rate, and calcining for 3h to obtain the lithium iron phosphate/multilayer graphene composite material.
Instantiation 2
Mixing 8ml of DMF (dimethyl formamide) with 2ml of distilled water to serve as a mixed solvent, adding 20mg of expanded graphite, carrying out ultrasonic oscillation for 2 hours to obtain a required multilayer graphene solution, and adding 200mg of CH (carbon-hydrogen) into the mixed solution3COONa and 90mg FeCl2·4H2O, magnetically stir for 8 minutes. Then transferred to a water bath kettle, and stirred for 2 hours in a water bath at the temperature of 90 ℃ and the rotating speed of 320 r/min. Taking out reactants, respectively centrifuging 3 times by using alcohol and distilled water to obtain an iron oxide/multilayer graphene composite sample, then adding 10ml of distilled water and 40.5mg of lithium dihydrogen phosphate crystals, stirring at normal temperature for 5 minutes until the lithium dihydrogen phosphate crystals are dissolved, transferring to a water bath kettle, stirring in water bath at the rotating speed of 70 ℃ and 320r/min for 2 hours, after that, placing in a 70 ℃ drying oven for drying for 24 hours, grinding the dried product for half an hour, transferring to a tubular furnace, heating to 650 ℃ at the speed of 3 ℃/min under the protection of nitrogen-hydrogen atmosphere, and calcining for 5 hours to obtain the lithium iron phosphate/multilayer graphene composite material.
Instantiation 3
Mixing 8ml of DMF (dimethyl formamide) with 2ml of distilled water to serve as a mixed solvent, adding 20mg of expanded graphite, carrying out ultrasonic oscillation for 5 hours to obtain a required multilayer graphene solution, and adding 200mg of CH (carbon-hydrogen) into the mixed solution3COONa and 120mg FeCl2·4H2O, magnetically stir for 5 minutes. Then transferred to a water bath kettle, and stirred for 2 hours in a water bath at the temperature of 90 ℃ and the rotating speed of 320 r/min. Taking out reactants, respectively centrifuging 3 times by using alcohol and distilled water to obtain an iron oxide/multilayer graphene composite sample, then adding 10ml of distilled water and 54mg of lithium dihydrogen phosphate crystals, stirring for 5 minutes at normal temperature until the solution is dissolved, transferring to a water bath kettle, stirring in water bath at the rotating speed of 70 ℃ and 320r/min for 2 hours, after that, placing in a 70 ℃ oven for drying for 24 hours, grinding the dried product for half an hour, transferring to a tubular furnace, heating to 650 ℃ at the speed of 3 ℃/min under the protection of nitrogen and hydrogen atmosphere, and calcining for 10 hours to obtain the lithium iron phosphate/multilayer graphene composite material.
Instantiation 4
8ml of DMF was mixed with 2ml of distilled water as a mixed solvent, and 20mg of DMF was addedExpanding graphite, carrying out ultrasonic oscillation for 5 hours to obtain a required multilayer graphene solution, and adding 200mgCH into the mixed solution3COONa and 100mg FeCl2·4H2O, magnetically stirring for 10 minutes. Then transferred to a water bath kettle, and stirred for 2 hours in a water bath at the temperature of 90 ℃ and the rotating speed of 320 r/min. Taking out reactants, respectively centrifuging 3 times by using alcohol and distilled water to obtain an iron oxide/multilayer graphene composite sample, then adding 10ml of distilled water and 45mg of lithium dihydrogen phosphate crystals, stirring for 5 minutes at normal temperature until the solution is dissolved, transferring to a water bath kettle, stirring in water bath at the rotating speed of 70 ℃ and 320r/min for 2 hours, after that, placing in a 70 ℃ drying oven for drying for 24 hours, grinding the dried product for half an hour, transferring to a tubular furnace, heating to 650 ℃ at the speed of 3 ℃/min under the protection of nitrogen and hydrogen gas atmosphere, and calcining for 2 hours to obtain the lithium iron phosphate/multilayer graphene composite material.
Fig. 2 is a Scanning Electron Microscope (SEM) observation image of the sample obtained in this example, and it can be seen from the image that the surface of the multilayer graphene is uniformly covered with lithium iron phosphate particles, and the particles are uniformly distributed, the particle diameter of the particles is about 100 to 200nm, the particle dispersibility is good, and voids exist between the lithium iron phosphate particles. Therefore, the original shape can be kept when the multilayer graphene is deformed, the flexible energy storage battery is quite suitable for application requirements of the flexible energy storage battery, and the flexible energy storage battery has good research and application prospects.
Fig. 3 is a pattern obtained by subjecting the sample obtained in this example to X-ray diffraction diffractometry (XRD), and a diffraction peak of a graphite layer of multilayer graphene and a diffraction peak of lithium iron phosphate can be observed, and the diffraction peak of lithium iron phosphate in the pattern coincides with a diffraction peak of lithium iron phosphate having a standard olivine structure.
And (2) taking the obtained composite material as an active material, putting the active material, conductive agent acetylene black and binder PVDF into a crucible according to the mass ratio of 80:10:10, adding a dispersing agent NMP to adjust the concentration, mixing and stirring for 4 hours, uniformly coating the uniformly stirred slurry on a treated aluminum foil current collector by using a blade coating method, and finally drying and evaporating the dispersing agent at 80 ℃ under a vacuum condition to obtain the required positive active material. Finally, the circular pole piece with the diameter of 16mm is cut and assembled to be tested.
The specific assembly process is as follows: half-cells were assembled using CR2032 coin cells in a glove box filled with argon gas under humidity and oxygen concentration below 1 ppm. The lithium iron phosphate/multilayer graphene is used as a positive electrode, Celgard 2300 is used as a diaphragm, and 1m LiPF6 dissolved in Ethylene Carbonate (EC) and diethyl carbonate (DEC) (volume ratio of 1: 1) is used as electrolyte. In the charge and discharge test system, the charge and discharge test voltage is 2.2V-4.2V.
Fig. 4 is a first charge-discharge curve of the electrode prepared from the composite material at 0.1C (the weight used is calculated by the total mass of the composite material), and a significant charge-discharge platform can be seen from the curve, which proves that the composite material has excellent redox performance.
Fig. 5 is a specific capacitance curve of an electrode prepared from the composite material tested under different multiplying power of charge and discharge currents (0.1C,0.5C,1C,2, C,5C,10C,0.1C, based on the theoretical capacity of lithium iron phosphate of 170 mAh/g). It can be seen from the figure that the composite material has good stability under the test conditions of different multiplying power. Although the capacity is not very high, one factor is that the lithium iron phosphate particles are too small and have many grain boundaries, thereby affecting the lithium storage capacity. Another factor is that the carbon proportion of the composite material is large, about 30% to 40% of carbon, thereby affecting the lithium storage capacity as a positive electrode material.
Fig. 6 is a cycle performance graph of 100 charging and discharging times at 0.5C of an electrode prepared from the composite material, and it can be seen from the graph that the capacity retention rate is 97% after 100 cycles, which proves that the material has good cycle stability.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.

Claims (9)

1. The lithium iron phosphate/multilayer graphene composite material is characterized in that lithium iron phosphate particles are loaded on the surface of multilayer graphene, wherein the lithium iron phosphate particles are formed by in-situ growth of uniform ferric oxide on the surface of the multilayer graphene and then transformation; the multilayer graphene is prepared by an ultrasonic method;
the preparation method of the composite material comprises the following steps:
step S1, preparing an iron oxide/multilayer graphene composite material;
step S2, converting iron oxide in the iron oxide/multilayer graphene composite material into lithium iron phosphate to form a lithium iron phosphate/multilayer graphene composite material;
wherein the step S1 further comprises the steps of:
s10: weighing dimethyl formamide DMF and distilled water in a volume ratio of 8:2, and mixing to obtain a mixed solvent;
s11: adding expanded graphite, and performing ultrasonic oscillation to obtain a multilayer graphene suspension;
s12: adding anhydrous sodium acetate and ferrous chloride tetrahydrate into the multilayer graphene suspension, stirring at normal temperature for 5-10 minutes until the anhydrous sodium acetate and the ferrous chloride tetrahydrate are fully dissolved, then transferring the multilayer graphene suspension into a water bath kettle, stirring in a water bath at 90 ℃ for 2 hours, taking out, and then continuously stirring at room temperature for 5 minutes until cooling; taking out the reactant, and centrifugally cleaning the reactant by using alcohol and distilled water to obtain the iron oxide/multilayer graphene composite material;
the step S2 further includes the steps of:
s20: adding distilled water and lithium dihydrogen phosphate which are equal in volume to the original mixed solvent into the centrifuged iron oxide/multilayer graphene composite material, stirring at room temperature for 5 minutes until the mixture is dissolved, then transferring the mixture into a water bath kettle, stirring in a water bath at 70 ℃ for 2 hours, taking out, and drying in an oven at 70 ℃ for 24 hours;
s21: and grinding the dried composite material for half an hour, transferring the ground composite material into a tubular furnace, and calcining the composite material for 2-10 hours at 650 ℃ under the protection of a nitrogen-hydrogen atmosphere to obtain the lithium iron phosphate/multilayer graphene composite material.
2. The lithium iron phosphate/multilayer graphene composite material according to claim 1, wherein the particle size of the lithium iron phosphate particles is 100 to 200 nm.
3. The lithium iron phosphate/multilayer graphene composite material according to claim 1, wherein in step S11, the amount of expanded graphite added to the mixed solvent is 2 mg/ml.
4. The lithium iron phosphate/multilayer graphene composite material according to claim 1, wherein in step S11, the ultrasonic oscillation time is 2 to 5 hours.
5. The lithium iron phosphate/multilayer graphene composite material according to claim 1, wherein in step S12, the addition amount of ferrous chloride tetrahydrate relative to the mixed solvent is 8-12 mg/ml, and the addition amount of anhydrous sodium acetate relative to the mixed solvent is 20 mg/ml.
6. The lithium iron phosphate/multi-layer graphene composite material of claim 1, wherein in step S20, the addition amount of lithium dihydrogen phosphate is determined by the addition amount of ferrous chloride tetrahydrate in step S12, wherein the molar ratio of Li ions to Fe ions is 1: 1.15.
7. the lithium iron phosphate/multilayer graphene composite material of claim 1, wherein in step S21, under the protection of a nitrogen-hydrogen mixed gas, the material is heated to 650 ℃ at a rate of 3 ℃/min and maintained for 2-10h, wherein the nitrogen-hydrogen mixed gas comprises the following components: 95% of nitrogen and 5% of hydrogen.
8. The lithium iron phosphate/multilayer graphene composite material according to claim 1, wherein lithium iron phosphate is uniformly distributed on the surface of graphene, and the particle size of lithium iron phosphate particles is mainly distributed in the range of 100nm to 200 nm.
9. The lithium ion battery is characterized in that the lithium iron phosphate/multilayer graphene composite material of any one of claims 1 to 8 is adopted as a positive electrode material of the lithium ion battery.
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CN105742629B (en) * 2014-12-09 2018-10-26 北京有色金属研究总院 A kind of in-situ preparation method of lithium ion battery anode material lithium iron phosphate/graphene complex
CN107170977B (en) * 2017-06-07 2020-05-05 安徽师范大学 Preparation method of lithium iron phosphate/graphene composite material, lithium ion battery anode and lithium ion battery
CN108400310B (en) * 2018-03-15 2020-04-21 湖南烯能新材料有限公司 Lithium ion battery anode material and preparation method thereof

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