CN109616633B - Preparation method of nano flaky manganese phosphate lithium ion battery cathode material - Google Patents

Preparation method of nano flaky manganese phosphate lithium ion battery cathode material Download PDF

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CN109616633B
CN109616633B CN201811449175.5A CN201811449175A CN109616633B CN 109616633 B CN109616633 B CN 109616633B CN 201811449175 A CN201811449175 A CN 201811449175A CN 109616633 B CN109616633 B CN 109616633B
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lithium
expanded graphite
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manganese
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CN109616633A (en
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舒洪波
吕途安
黄成�
闵豪
孙婷婷
韩明雨
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Xiangtan 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
    • H01M4/366—Composites as layered products
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • 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
    • H01M4/62—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
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • 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 application relates to a preparation method of a nano flaky lithium manganese phosphate anode material growing in situ on the surface of expanded graphite, which enables lithium manganese phosphate particles to have good dispersibility through the inhibiting effect of the expanded graphite on the crystal growth and agglomeration of the material in the reaction process, and meanwhile, under the combined action of a solvent containing hydroxyl and the expanded graphite, the lithium manganese phosphate nanosheets grow along (020) dominant crystal faces beneficial to lithium ion intercalation and deintercalation, and are compounded with the expanded graphite in a surface-to-surface contact manner to form a good conductive network, so that the rate capability and the cycling stability of the material are greatly improved. The material can meet the requirement of rapid charge and discharge of the power lithium ion battery under large current, and has good application prospect in the field of power batteries.

Description

Preparation method of nano flaky manganese phosphate lithium ion battery cathode material
Technical Field
The invention relates to the field of lithium ion battery anode materials and electrochemistry, in particular to a preparation method of a nano flaky lithium manganese phosphate anode material growing on the surface of expanded graphite in situ.
Background
With the increasing demand for electric vehicles and hybrid vehicles, the development of lithium ion battery cathode materials is increasing. Lithium iron phosphate is an important representative of the anode material of the lithium ion battery, and the commercial application of the lithium iron phosphate is mature. The lithium manganese phosphate with the same crystal structure as that of the lithium iron phosphate has a high theoretical capacity of 170mAhg < -1 >, the cycling stability is close to that of the lithium iron phosphate, the energy density of the full cell is improved by about 20% compared with that of the lithium iron phosphate due to a 4.1V high-voltage platform possessed by the lithium manganese phosphate, the material is highly concerned by people, the material is considered to be a most promising substitute of a commercialized cathode material, and due to the defects of poor conductivity, low ion diffusion rate and the like caused by the self-structure, the material has the problems of serious capacity decline after long-time cycling, poor rate capability and the like, and the application and development of the material are greatly limited.
The existing method for improving the electrochemical performance of the manganese lithium phosphate mainly comprises the following steps: firstly, manganese phosphate lithium nano particles with special crystal faces are synthesized, and the research on the molecular structure of the manganese phosphate lithium finds that lithium ions in the manganese phosphate lithium molecules are subjected to one-dimensional diffusion along the (010) direction, so that the ion diffusion distance is shortened, and the ion diffusion rate is increased to become a main method for improving the electrochemical performance of the manganese phosphate lithium. Such as [ J ]
Hui Guo et al journal of Materials Chemistry A.2014, 2, 10581-. And secondly, coating a conductive coating on the surface to improve the conductivity of the lithium manganese phosphate. In recent years, graphene and reduced graphene oxide are used as carbon materials in a plurality of electrode active materials, but the graphene and the reduced graphene oxide are easy to agglomerate, and the conductivity of the graphene and the reduced graphene oxide is reduced due to incomplete reduction of oxygen-containing functional groups on the surface. Meanwhile, the graphene or the reduced graphene oxide serving as a loading surface and electrochemical active material particles have different contact modes, such as point-surface contact, line-surface contact and other low-efficiency electronic contact modes, which also affect the conductivity of the material, so that the improvement on the electrochemical performance is very limited, and the conductivity of the graphene or the reduced graphene oxide can be fully utilized by adopting the surface-surface contact mode. The expanded graphite serving as a graphite material has a high specific surface area close to that of graphite and a special layered structure, so that the graphite material is not easy to agglomerate, and compared with graphene oxide, the amount of oxygen-containing functional groups of the expanded graphite is greatly reduced, so that the conductivity of the material can be greatly improved by adopting the expanded graphite as a conductive network.
The invention tries to utilize the characteristic that the surface of the expanded graphite has partial oxygen-containing functional groups and simultaneously combines an organic solvent containing hydroxyl to carry out solvothermal reaction, so that the manganese phosphate lithium nanosheet with (020) dominant crystal face grows in situ on the surface of the expanded graphite, the particles have good dispersibility and are in contact with the expanded graphite in a surface-surface contact manner, and the prepared material has excellent circulation stability and rate capability, particularly high rate capability, and meets the requirements of electric automobiles and hybrid electric automobiles on the anode material of the lithium ion battery.
Disclosure of Invention
The technical problem to be solved by the invention is as follows: in order to solve the defects in the prior art, the preparation method of the nano flaky manganese phosphate lithium ion battery anode material is provided.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a preparation method of a nano flaky manganese phosphate lithium ion battery anode material comprises the following steps:
adding expanded graphite into an organic matter containing alcohols, dissolving lithium salt into the organic matter to prepare a solution A, wherein the concentration of lithium ions in the solution A is 0.1-3.5mol/L, and the mass ratio of lithium elements to the expanded graphite is 2.5-7: 1;
dissolving a phosphorus source in an organic matter containing alcohols to prepare a solution B with the concentration of phosphate radical of 0.03-2.6mol/L, adding the solution B into the solution A, and stirring to prepare a solution C, wherein the volume ratio of the solvent of the solution B to the solvent of the solution A is 0.4-0.8: 1;
dissolving a manganese source in a mixed solvent of an alcohol organic matter and water to prepare a solution D with the manganese ion concentration of 0.025-2.2 mol/L;
mixing the solution D with the solution C under the condition of stirring, wherein the volume ratio of the solvent of the solution D to the solvent of the solution A is 0.5-1.0: 1, the reaction temperature is controlled at 140-220 ℃, the reaction time is 6-20h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with alcohol and deionized water until the pH value of the filtrate is 6-7, and drying to obtain precursor powder;
And mixing the precursor powder with a carbon source, heating to 900 ℃ under protective gas, preserving the heat for 2-8h, and cooling to room temperature along with the furnace to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
Preferably, in the preparation method of the invention, the expanded graphite is obtained by calcining graphite oxide at the temperature of 900 ℃ under the protection gas for 1-4 h;
the expanded graphite is added into a solvent and is subjected to ultrasonic action for more than 1 hour.
Preferably, the preparation method of the present invention,
the organic solvent containing alcohols is ethanol or ethylene glycol, or a mixture of ethanol, ethylene glycol and deionized water.
Preferably, in the preparation method of the present invention, the manganese source is at least one of manganese sulfate, manganese acetate and manganese nitrate.
Preferably, in the preparation method of the present invention, the phosphorus source is at least one of phosphoric acid and ammonium dihydrogen phosphate.
Preferably, in the preparation method of the present invention, the carbon source is at least one of sucrose, glucose, dopamine, polypyrrole, phenolic resin, cetyl trimethyl ammonium bromide, and polyvinylpyrrolidone.
Preferably, in the preparation method of the present invention, the lithium salt is at least one of lithium acetate, lithium hydroxide and lithium carbonate.
Preferably, in the preparation method of the invention, after the precursor powder is mixed with the carbon source, the heating rate of the heating is 2-6 ℃/min.
Preferably, the preparation method of the present invention is characterized in that: the protective gas is nitrogen, argon or a mixed gas of nitrogen and hydrogen, or a mixed gas of argon and hydrogen; in the mixed gas of the nitrogen and the hydrogen, the nitrogen accounts for 80-99V%, and the hydrogen accounts for 1-20V%; in the mixed gas of argon and hydrogen, the argon accounts for 80-99V%, and the hydrogen accounts for 1-20V%.
The nano flaky manganese phosphate lithium ion battery cathode material is prepared by the preparation method.
The invention has the beneficial effects that:
(1) the invention adopts a solvothermal method to synthesize the nano flaky lithium manganese phosphate anode material which grows on the surface of the expanded graphite in situ, and has the advantages of simple synthesis process, good repeatability and the like.
(2) The invention synthesizes the nano flaky lithium manganese phosphate anode material growing in situ on the surface of the expanded graphite, wherein the expanded graphite has the inhibiting effect on the crystal growth and agglomeration of the material in the reaction process, so that lithium manganese phosphate particles have good dispersibility, and meanwhile, under the combined action of a solvent containing hydroxyl and the expanded graphite, the lithium manganese phosphate nanosheet grows along a (020) dominant crystal face beneficial to the intercalation and deintercalation of lithium ions, and the lithium manganese phosphate nanosheet and the expanded graphite are compounded in a surface-to-surface contact form to form a good conductive network, thereby greatly improving the rate capability and the cycling stability of the material. The material can meet the requirement of rapid charge and discharge of the power lithium ion battery under large current, and has good application prospect in the field of power batteries.
Drawings
The technical solution of the present application is further explained below with reference to the drawings and the embodiments.
Fig. 1 is an X-ray diffraction (XRD) pattern of the nano-flake lithium manganese phosphate cathode material grown in situ on the surface of expanded graphite in example 1.
Fig. 2 is a Scanning Electron Microscope (SEM) image and a Transmission Electron Microscope (TEM) image of the nano-flake lithium manganese phosphate cathode material grown in situ on the surface of the expanded graphite in example 1.
Fig. 3 is a first charge-discharge curve of the nano-sheet lithium manganese phosphate cathode material grown in situ on the surface of the expanded graphite in example 1.
Fig. 4 is a graph showing cycle performance of the nano-flake lithium manganese phosphate cathode material grown in situ on the surface of the expanded graphite in example 1.
Fig. 5 is a graph showing rate performance of the nano-flake lithium manganese phosphate cathode material grown in situ on the surface of the expanded graphite in example 1.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.
The technical solutions of the present application will be described in detail below with reference to the accompanying drawings in conjunction with embodiments.
Example 1
The preparation method of the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ comprises the following steps:
(1) Firstly, calcining graphite oxide at 400 ℃ for 2h under the protection of argon to obtain expanded graphite;
(2) adding the product obtained in the step (1) into 20mL of glycol solvent, performing ultrasonic dispersion for 1h, dissolving lithium hydroxide in the solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.1mol/L, wherein the mass ratio of the lithium element to the expanded graphite is 2.5: 1;
(3) dissolving phosphoric acid in 15mL of ethylene glycol to prepare a solution B with the phosphate radical concentration of 0.03mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese sulfate was dissolved in 18mL (ratio of ethylene glycol to water 5: 1) to prepare a solution D having a manganese ion concentration of 0.025 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 140 ℃ and the reaction time at 6h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 6, and carrying out forced air drying at 60 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with cane sugar, placing the mixture in a reaction kiln, heating to 500 ℃ at a speed of 2 ℃/min under the protection of argon, preserving the temperature for 2 hours, and cooling to room temperature along with the kiln to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
Fig. 1 is an XRD pattern of LiMnPO4@ EG @ C positive electrode material obtained in example 1 of the present invention. As can be seen from figure 1, the material has sharp diffraction peak, higher crystallinity and perfect crystal grain development. Fig. 2a is an SEM of LiMnPO4@ EG @ C positive electrode material obtained in example 1 of the present invention, and fig. 2b is a TEM of LiMnPO4@ EG @ C positive electrode material obtained in example 1 of the present invention, and it can be seen from the two figures that lithium manganese phosphate nanosheets having an average particle diameter of about 20 to 150nm are grown on the surface and between layers of expanded graphite.
Taking N-methylpyrrolidone (NMP) as a solvent, uniformly mixing the LiMnPO4@ EG @ C material synthesized in the embodiment with polyvinylidene fluoride (PVDF) and acetylene black according to the mass ratio of 80: 10, coating the mixture on an aluminum foil to prepare a positive electrode piece, then taking a lithium piece as a negative electrode, assembling the lithium ion battery, and measuring the first discharge specific capacity of the lithium ion battery to be up to 142mAh/g under the conditions of 0.2C (1C: 170mA/g) and 2.0-4.5V at room temperature, wherein the figure is shown in figure 3; the capacity retention rate after 200 cycles under the conditions of 1C and 2.0-4.5V is 100%, as shown in FIG. 4; under the conditions of 10C and 2.0-4.6V, the first discharge specific capacity is 103mAh/g, and after 1000 times of circulation, the discharge specific capacity is 72mAh/g, and electrochemical tests show that compared with a comparative example, the LiMnPO4@ EG @ C material synthesized in the embodiment has the advantages that the capacity retention rate is obviously improved, relatively high discharge specific capacity and circulation stability are still achieved under the condition of high current density, and the electrochemical performance is excellent.
Example 2
The preparation method of the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide at 700 ℃ for 4h under the protection of nitrogen to obtain expanded graphite;
(2) adding the product obtained in the step (1) into a solvent of 40mL of alcohol, performing ultrasonic dispersion for 2h, dissolving lithium acetate in the solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.3mol/L, wherein the mass ratio of lithium element to expanded graphite is 5: 1;
(3) dissolving ammonium dihydrogen phosphate in 16mL of ethylene glycol to prepare a solution B with the phosphate radical concentration of 0.09mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese acetate was dissolved in 20mL (ratio of ethylene glycol to water was 4: 1) to prepare a solution D having a manganese ion concentration of 0.12 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 160 ℃ and the reaction time at 8h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 7, and carrying out forced air drying at 80 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with hexadecyl trimethyl ammonium bromide, placing the mixture in a reaction kiln, heating to 600 ℃ at a speed of 4 ℃/min under the protection of nitrogen, preserving heat for 2 hours, and cooling to room temperature along with the kiln to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the example 1, and electrochemical tests show that the specific discharge capacity is 145.4mAh/g, 131mAh/g, 123mAh/g, 118mAh/g, 115mAh/g, 102mAh/g, 82mAh/g and 70mAh/g respectively at the multiplying power of 0.2C, 0.5C, 1C, 2C, 5C, 10C, 20C and 30C, which are shown in figure 5.
Example 3
The preparation method of the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide at 800 ℃ for 2h under the protection of atmosphere (the mixed gas of nitrogen and hydrogen (the nitrogen accounts for 80V percent and the hydrogen accounts for 20V percent) to obtain expanded graphite;
(2) adding the product obtained in the step (1) into 30mL of mixed solvent of deionized water and ethylene glycol, carrying out ultrasonic dispersion for 1h, dissolving lithium carbonate in the mixed solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.2mol/L, wherein the mass ratio of lithium element to expanded graphite is 7: 1;
(3) Dissolving phosphoric acid in 15mL of deionized water and ethylene glycol to prepare a solution B with the phosphate radical concentration of 0.12mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese nitrate was dissolved in 18mL (ratio of ethylene glycol to water was 5: 1) to prepare a solution D having a manganese ion concentration of 0.14 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 180 ℃ and the reaction time at 10h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 7, and performing forced air drying at 90 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with dopamine, placing the mixture in a reaction kiln, heating to 600 ℃ at a speed of 4 ℃/min under the protection of a mixed gas of nitrogen and hydrogen (the nitrogen accounts for 80V%, and the hydrogen accounts for 20V%), preserving the heat for 4h, and cooling to room temperature along with the furnace to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 137mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate is 98% after one 200 times of circulation under the conditions of 1C and 2.0-4.5V, and good electrochemical performance is shown.
Example 4
The nano flaky lithium manganese phosphate cathode material growing on the surface of expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide at 800 ℃ for 4h under the protection of atmosphere to obtain expanded graphite;
(2) adding the product obtained in the step (1) into a solvent of 35mL ethanol, performing ultrasonic dispersion for 1.5h, dissolving lithium hydroxide in the solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.3mol/L, wherein the mass ratio of lithium element to expanded graphite is 5: 1;
(3) ammonium dihydrogen phosphate was dissolved in 15mL (ratio of ethanol to water was 4: 1) to prepare a solution B having a phosphate concentration of 0.09mol/L, and the solution B was added to the solution A with stirring to obtain a solution C.
(4) Manganese sulfate was dissolved in 18mL (ratio of ethanol to water 5: 1) to prepare a solution D having a manganese ion concentration of 1.1 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 200 ℃ and the reaction time at 15h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 7, and carrying out forced air drying at 90 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with polypyrrole, placing the mixture in a reaction kiln, heating to 650 ℃ at a speed of 5 ℃/min under the protection of a mixed gas of nitrogen and hydrogen (the nitrogen accounts for 99V%, and the hydrogen accounts for 1V%), preserving heat for 6 hours, and cooling to room temperature along with the kiln to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 139mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate is 95% after 200 times of circulation under the conditions of 1C and 2.0-4.5V, and good electrochemical performance is shown.
Example 5
The nano flaky lithium manganese phosphate cathode material growing on the surface of expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide for 2 hours at 800 ℃ under the protection of atmosphere (the mixed gas of argon and hydrogen (the argon accounts for 80V percent and the hydrogen accounts for 20V percent)) to obtain expanded graphite;
(2) adding the product obtained in the step (1) into 40mL of glycol solvent, performing ultrasonic dispersion for 1h, dissolving lithium hydroxide in the solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.4mol/L, wherein the mass ratio of lithium element to expanded graphite is 5: 1;
(3) Dissolving phosphoric acid in 30mL (the ratio of ethylene glycol to water is 4: 1) to prepare a solution B with the phosphate radical concentration of 0.09mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese sulfate is dissolved in 20mL of ethylene glycol to prepare a solution D with the manganese ion concentration of 2.0/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 220 ℃ and the reaction time at 20h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 6.5, and carrying out forced air drying at 100 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with polyvinylpyrrolidone, placing the mixture in a reaction kiln, heating to 400 ℃ at a speed of 5 ℃/min under the protection of a mixed gas of argon and hydrogen (the argon accounts for 80V%, the hydrogen accounts for 20V%), preserving the heat for 8h, and cooling to room temperature along with the furnace to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 141mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate is 100% after one 200 times of circulation under the conditions of 1C and 2.0-4.5V, and the electrochemical performance is good.
Example 6
The nano flaky lithium manganese phosphate cathode material growing on the surface of expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide at 900 ℃ for 2h under the protection of atmosphere to obtain expanded graphite;
(2) adding the product obtained in the step (1) into a solvent of 30mL of ethanol, performing ultrasonic dispersion for 1h, dissolving lithium hydroxide in the solvent after the ultrasonic treatment is finished, and preparing a uniform solution A with the lithium ion concentration of 0.4mol/L, wherein the mass ratio of lithium element to expanded graphite is 5: 1;
(3) dissolving phosphoric acid in 20mL (the ratio of ethanol to water is 4: 1) to prepare a solution B with the phosphate radical concentration of 2.0mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese sulfate is dissolved in 20mL of ethanol to prepare a solution D with the manganese ion concentration of 2.2/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 220 ℃ and the reaction time at 20h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 6.5, and carrying out forced air drying at 100 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with glucose, placing the mixture in a reaction kiln, heating to 700 ℃ at a speed of 5 ℃/min under the protection of a mixed gas of argon and hydrogen (the argon accounts for 95V%, the hydrogen accounts for 5V%), preserving the temperature for 8h, and cooling to room temperature along with the furnace to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 136mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate after 200 times of circulation under the conditions of 1C and 2.0-4.5V is 94%, and the electrochemical performance is good.
Example 7
The nano flaky lithium manganese phosphate cathode material growing on the surface of expanded graphite in situ comprises the following steps:
(1) firstly, calcining graphite oxide at 900 ℃ for 2h under the protection of atmosphere to obtain expanded graphite;
(2) adding the product obtained in the step (1) into a solvent of 30mL of ethanol, performing ultrasonic dispersion for 1h, dissolving lithium hydroxide in the solvent after the ultrasonic dispersion is finished, and preparing a uniform solution A with the lithium ion concentration of 3.5mol/L, wherein the mass ratio of lithium element to expanded graphite is 5: 1;
(3) dissolving phosphoric acid in 24mL (the ratio of ethanol to water is 4: 1) to prepare a solution B with the phosphate concentration of 2.6mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese sulfate is dissolved in 30mL of ethanol to prepare a solution D with the manganese ion concentration of 0.1 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 220 ℃ and the reaction time at 20h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 6.5, and carrying out forced air drying at 100 ℃ to obtain precursor powder.
(6) And (3) mixing the precursor powder obtained in the step (5) with phenolic resin, placing the mixture in a reaction kiln, heating to 900 ℃ at the speed of 6 ℃/min under the protection of the mixed gas of argon and hydrogen (the argon accounts for 99V% and the hydrogen accounts for 1V%), preserving the temperature for 8h, and cooling to room temperature along with the kiln to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 128mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate is 93% after one/200 times of circulation under the conditions of 1C and 2.0-4.5V, and good electrochemical performance is shown.
Comparative example
(1) Lithium hydroxide was dissolved in 30mL of ethylene glycol to prepare a uniform solution A having a lithium ion concentration of 0.6 mol/L.
(3) Dissolving phosphoric acid in 30mL (the ratio of ethylene glycol to water is 4: 1) to prepare a solution B with the phosphate radical concentration of 0.4mol/L, and adding the solution B into the solution A under the stirring condition to obtain a solution C.
(4) Manganese sulfate is dissolved in 30mL of ethylene glycol to prepare a solution D with the manganese ion concentration of 0.4 mol/L. Solution D was mixed with solution C with stirring.
(5) Transferring the mixed solution obtained in the step (4) into a stainless steel reaction kettle with a polytetrafluoroethylene material lining, sealing and then placing in a drying box; controlling the reaction temperature at 200 ℃ and the reaction time at 10h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with ethanol and deionized water until the pH value of the filtrate is 6.5, and performing forced air drying at 100 ℃ to obtain precursor powder.
(6) Mixing the precursor powder obtained in the step (5) with glucose, placing the mixture in a reaction kiln, and performing Ar/H reaction2(Ar 95V%, H)25V%) is heated to 600 ℃ at a speed of 5 ℃/min, and is cooled to room temperature along with the furnace after heat preservation for 2 hours, thus obtaining the nano flaky lithium manganese phosphate anode material.
The lithium ion battery is prepared by the same method as the embodiment 1, and the electrochemical test shows that the first discharge specific capacity is 110mAh/g in the voltage range of 0.2C and 2.0-4.5V; the capacity retention rate is 85% after circulation for 200 times under the conditions of 1C and 2.0-4.5V, the specific discharge capacity is 110.4mAh/g, 102mAh/g, 90mAh/g, 72mAh/g, 51mAh/g, 34mAh/g, 22mAh/g and 3mAh/g under the multiplying power of 0.2C, 0.5C, 1C, 2C, 5C, 10C, 20C and 30C respectively, compared with the electrochemical performance of the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ, the method proves that the particles prepared by the method that the lithium manganese phosphate nanosheet with the (020) crystal face advantage grows on the surface of the expanded graphite in situ have good dispersibility by utilizing the characteristic that the surface of the expanded graphite has partial oxygen-containing functional groups and combining with an organic solvent containing hydroxyl to carry out solvothermal reaction, and the lithium manganese phosphate anode material of the expanded graphite is in contact with the lithium phosphate anode material of the expanded graphite in a surface-surface contact way of surface-surface contact, has excellent cycle stability and rate capability.
In light of the foregoing description of the preferred embodiments according to the present application, it is to be understood that various changes and modifications may be made without departing from the spirit and scope of the invention. The technical scope of the present application is not limited to the contents of the specification, and must be determined according to the scope of the claims.

Claims (10)

1. A preparation method of a nano flaky manganese phosphate lithium ion battery anode material is characterized by comprising the following steps:
adding expanded graphite into a solvent containing an alcohol organic matter, and dissolving lithium salt into the solvent to prepare a solution A, wherein the concentration of lithium ions in the solution A is 0.1-3.5mol/L, and the mass ratio of lithium elements to the expanded graphite is 2.5-7: 1;
dissolving a phosphorus source in a solvent containing an alcohol organic matter to prepare a solution B with the phosphate radical concentration of 0.03-2.6mol/L, adding the solution B into the solution A, and stirring to prepare a solution C, wherein the volume ratio of the solvent of the solution B to the solvent of the solution A is 0.4-0.8: 1;
dissolving a manganese source in a mixed solvent of an alcohol organic matter and water to prepare a solution D with the manganese ion concentration of 0.025-2.2 mol/L;
mixing the solution D with the solution C under the condition of stirring, wherein the volume ratio of the solvent of the solution D to the solvent of the solution A is 0.5-1.0: 1, the reaction temperature is controlled at 140-220 ℃, the reaction time is 6-20h, after the reaction is finished, filtering the obtained product, repeatedly washing the product with alcohol and deionized water until the pH value of the filtrate is 6-7, and drying to obtain precursor powder;
And mixing the precursor powder with a carbon source, heating to 900 ℃ under protective gas, preserving the heat for 2-8h, and cooling to room temperature along with the furnace to obtain the nano flaky lithium manganese phosphate anode material growing on the surface of the expanded graphite in situ.
2. The preparation method as claimed in claim 1, wherein the expanded graphite is obtained by calcining graphite oxide under a protective gas at 400-900 ℃ for 1-4 h; the expanded graphite is added into a solvent and is subjected to ultrasonic action for more than 1 hour.
3. The method according to claim 2, wherein the organic solvent containing alcohol is ethanol or ethylene glycol, or a mixture of ethanol, ethylene glycol and deionized water.
4. The production method according to any one of claims 1 to 3, wherein the manganese source is at least one of manganese sulfate, manganese acetate, and manganese nitrate.
5. The method according to any one of claims 1 to 3, wherein the phosphorus source is at least one of phosphoric acid and ammonium dihydrogen phosphate.
6. The method according to any one of claims 1 to 3, wherein the carbon source is at least one selected from sucrose, glucose, dopamine, polypyrrole, phenol resin, cetyltrimethylammonium bromide, and polyvinylpyrrolidone.
7. The production method according to any one of claims 1 to 3, wherein the lithium salt is at least one of lithium acetate, lithium hydroxide, and lithium carbonate.
8. The production method according to any one of claims 1 to 3, wherein the temperature rise rate of the precursor powder after mixing with the carbon source is 2 to 6 ℃/min.
9. The method of claim 2, wherein: the protective gas is nitrogen, argon or a mixed gas of nitrogen and hydrogen, or a mixed gas of argon and hydrogen; in the mixed gas of the nitrogen and the hydrogen, the nitrogen accounts for 80-99V%, and the hydrogen accounts for 1-20V%; in the mixed gas of argon and hydrogen, the argon accounts for 80-99V%, and the hydrogen accounts for 1-20V%.
10. The nano flaky manganese phosphate lithium ion battery cathode material is characterized by being prepared by the preparation method of any one of claims 1 to 9.
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