CN111740112B - Preparation method of lithium iron phosphate/carbon nanotube composite positive electrode material - Google Patents

Preparation method of lithium iron phosphate/carbon nanotube composite positive electrode material Download PDF

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CN111740112B
CN111740112B CN202010624186.3A CN202010624186A CN111740112B CN 111740112 B CN111740112 B CN 111740112B CN 202010624186 A CN202010624186 A CN 202010624186A CN 111740112 B CN111740112 B CN 111740112B
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lithium
iron
carbon nanotube
phosphate
nanotube composite
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CN111740112A (en
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王接喜
颜果春
李新海
席昭
王志兴
郭华军
胡启阳
彭文杰
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Central South 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
    • H01M4/58—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
    • 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

Compared with the traditional method, the invention utilizes the iron-based catalyst to induce the in-situ growth of the carbon nano tube with good dispersibility, and takes the carbon nano tube as the raw material to prepare the lithium iron phosphate/carbon nano tube composite anode material.

Description

Preparation method of lithium iron phosphate/carbon nanotube composite positive electrode material
Technical Field
The invention relates to the field of lithium ion battery materials, in particular to a preparation method of a lithium iron phosphate/carbon nanotube composite anode material.
Background
In 1991, sony corporation introduced the first commercial lithium ion battery, which uses lithium cobaltate as the positive electrode material and carbon as the negative electrode material, to effectively solve the problem of lithium dendrites, and therefore, the large-scale use of lithium ion batteries was drawn. Compared with other traditional secondary power supplies, the lithium ion battery has the characteristics of high energy density, high power density, high working voltage, long cycle life, environmental friendliness and the like, is ideal and one of the most widely applied energy storage devices at present, and particularly has wider and wider application prospect along with the rapid development of electric vehicles and large-scale energy storage fields in recent years. However, the cost and safety of lithium ion batteries still plague both academia and industry and have largely limited the rate of growth of lithium ion batteries.
The positive electrode material is used as an important component of the lithium ion battery, has a decisive effect on various indexes of the lithium ion battery, and the seeking of the positive electrode material with excellent performance is the key for further improving the comprehensive competitiveness of the lithium ion battery. The commercial lithium ion battery positive electrode material comprises lithium cobaltate, a ternary material, lithium manganate and lithium iron phosphate, wherein the lithium cobaltate and the ternary material both have a layered structure, and have higher specific capacity and working voltage ratio, but have the defects of high preparation cost and poor safety and stability; the lithium manganate has a spinel structure, is low in preparation cost, but has the defects of poor cycle performance and poor high-temperature performance; the lithium iron phosphate material has an olivine structure, rich raw material resources, relatively high specific capacity, long cycle life and good safety performance, and is an ideal material for electric vehicles and large-scale energy storage lithium ion batteries. However, the material has the defects of low lithium ion diffusion speed and low electronic conductivity, has strong electrochemical polarization phenomenon in the charge and discharge process, and has poor performance under the condition of high-rate discharge. Therefore, in the actual use process, the lithium iron phosphate material needs to be modified. The diffusion distance of lithium ions in material lattices can be shortened by controlling the particle size of the lithium iron phosphate material; by doping beneficial metal elements, the lithium iron phosphate material can generate lattice defects, so that the intrinsic conductivity and the lithium ion diffusion coefficient of the material are improved; by compounding the lithium iron phosphate material with the material with better conductivity, the conductivity among material particles can be improved, thereby achieving the purpose of improving the electrochemical performance of the material. In the composite material with good conductivity, the carbon material is the focus of research because the carbon material has good conductivity and can inhibit the growth of the particle size of the material to a certain extent. The carbon nanotube is a carbon material rolled by graphite and has a one-dimensional hollow tube structure, the outer layer electrons among carbon atoms can form sp2 hybridization, and the rest electrons form delocalized large pi bonds, so that electrons capable of freely moving exist in the carbon nanotube, and the conductivity of the carbon nanotube is very excellent. However, the carbon nanotube material has a large aspect ratio and a large specific surface area, which leads to serious agglomeration of the material, and it is difficult to obtain a uniformly dispersed material when the material is compounded with a lithium iron phosphate material in a conventional manner. Researchers have proposed that carbon nanotubes (CN102427130A, CN101533904A) are grown in situ in a lithium iron phosphate material by a vapor deposition method to improve the uniformity of the composite material, but the catalyst used in the deposition process is difficult to remove, which affects the purity of the final product.
Therefore, it is of great significance to develop a new method for preparing the lithium iron phosphate/carbon nanotube composite anode material with excellent electrochemical performance and uniform components.
Disclosure of Invention
The invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite anode material, and aims to solve the problem that a uniformly dispersed material is difficult to obtain when a conventional mode is adopted for compounding a lithium iron phosphate material and a carbon nanotube.
In order to achieve the above object, the present invention provides a method for preparing a lithium iron phosphate/carbon nanotube composite positive electrode material, comprising the steps of:
preparing an iron-based catalyst/carbon nanotube composite material from an iron-based catalyst and a gas-phase carbon source by adopting a chemical vapor deposition method;
step two, the iron-based catalyst/carbon nano tube composite material obtained in the step one is treated by adopting a chemical or electrochemical reaction, and one or more of an iron source, a phosphorus source, a lithium source and a doping element are supplemented in the reaction process to obtain a lithium iron phosphate precursor/carbon nano tube composite material;
adding a lithium source and a phosphorus source into the lithium iron phosphate precursor/carbon nanotube composite material obtained in the step two, and uniformly mixing to obtain a composite cathode material mixture;
and step four, performing high-temperature solid-phase sintering on the composite anode material mixture obtained in the step three in a protective atmosphere, and naturally cooling the mixture to room temperature along with the furnace to obtain the lithium iron phosphate/carbon nanotube composite anode material.
Preferably, in the first step, the content of iron in the iron-based catalyst is 50-100 wt%, and the other is a doping element, wherein the doping element is one or more of Ni, Co, Mn, Mg, Al, Ti, Cr, Zr or W; the particle size of the iron-based catalyst is 10-10000 nm; the iron-based catalyst is one or more of analytically pure grade, industrial grade or other iron-containing waste materials.
Preferably, in the first step, the carbon source is one of methane, ethane, propane, ethylene, propylene, acetylene, ethanol, ethylene glycol, propanol, isopropanol, cyclohexane, polyethylene or polyvinyl alcohol.
Preferably, in the first step, the flow rate of the gas-phase carbon source in the process of preparing the iron-based catalyst/carbon nanotube composite by the chemical vapor deposition method is 10-500 sccm, nitrogen or argon is used as a protective atmosphere, the gas flow rate of the protective gas is 100-1000 sccm, the reaction temperature of the chemical vapor deposition is 500-1200 ℃, and the reaction time is 1-10 hours.
Preferably, the chemical or electrochemical reaction in the second step is one or more of atmospheric pressure oxidation leaching, micro-galvanic cell enhanced leaching, coordination leaching, coprecipitation method, hydrothermal method, sol-gel method, solid phase method and controlled electrolysis method; the iron source is one or more of sulfate, nitrate, phosphate, acetate and oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, lithium phosphate and lithium dihydrogen phosphate; the lithium source is one or more of lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide and lithium acetate.
Preferably, the chemical formula of the lithium iron phosphate precursor in the second step is (Fe)xM1-x)yPO4Or (Fe)xM1-x)zO, wherein x is more than or equal to 0 and less than or equal to 0.5, y is more than or equal to 2/3 and less than or equal to 1, 0<z is less than or equal to 1.5, and M is one or more of Ni, Co, Mn, Cu, Zn, Mg, Al, Ti, Cr, Zr, W, Nb, Sn and Mo.
Preferably, the molar ratio of lithium, iron, doping elements and phosphorus in the composite cathode material mixture in the third step is Li: (Fe + M): p is 0.95-1.10: 0.95-1.05: 0.95 to 1.05; the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate or lithium dihydrogen phosphate.
Preferably, the temperature of the high-temperature solid-phase sintering of the composite anode material mixture in the fourth step is 500-900 ℃, and the time is 2-20 hours; the protective atmosphere is nitrogen or argon.
Preferably, in the fourth step, the content of the carbon nanotube in the lithium iron phosphate/carbon nanotube composite positive electrode material is 0.1-25 wt%, and the content of the lithium iron phosphate is 75-99.9 wt%.
According to the preparation method of the lithium iron phosphate/carbon nanotube composite anode material, the carbon nanotube with controllable appearance and good dispersibility is prepared by using the iron-based catalyst, and the electrical conductivity of the prepared composite anode material is improved by using the excellent electrical conductivity of the carbon nanotube. The carbon nano tube grown in situ by the iron-based catalyst is used as a raw material, and the iron-based catalyst is dissolved through chemical or electrochemical reaction and becomes a partial source of iron in the lithium iron phosphate precursor. By the method, a large number of nucleation sites are provided for the carbon nano tube in the process of preparing the lithium iron phosphate precursor, and finally the lithium iron phosphate material with smaller particle size can be obtained, which is beneficial to reducing the path of lithium ion diffusion in the process of charging and discharging the material. Meanwhile, the carbon nanotubes are uniformly dispersed in the process of forming the lithium iron phosphate precursor, so that the carbon nanotubes and the lithium iron phosphate material in the composite anode material prepared by the method can form a mutual-embedded structure, namely the carbon nanotubes construct a good conductive network, and the lithium iron phosphate material is uniformly distributed in the conductive network. In addition, beneficial element doping is introduced, so that the activation energy of electron migration in the lithium iron phosphate material can be reduced, the intrinsic conductivity of the material is improved, and the conductivity of the composite material is improved together with the carbon nano tube. In addition, the invention makes full use of the iron-based catalyst in the preparation process of the carbon tube, omits the procedures of acid washing and impurity removal in the preparation process of the carbon tube, and obviously reduces the comprehensive cost of the lithium iron phosphate/CNTs.
The scheme of the invention has the following beneficial effects:
1. the carbon nanotube provides a large number of nucleation sites in the process of preparing the lithium iron phosphate precursor, and finally the lithium iron phosphate material with smaller particle size can be obtained, thereby being beneficial to reducing the path of lithium ion diffusion in the charging and discharging process of the material and improving the performance of the battery.
2. The carbon nano tubes and the lithium iron phosphate material in the composite anode material prepared by the method can form a mutual-embedding structure, namely, the carbon nano tubes construct a good conductive network, and the lithium iron phosphate material is uniformly distributed in the carbon nano tubes.
3. The invention introduces beneficial element doping, can reduce the activation energy of electron migration in the lithium iron phosphate material, improves the intrinsic conductivity of the material, and improves the conductivity of the composite material together with the carbon nano tube.
4. The lithium iron phosphate/carbon nanotube composite anode material prepared by the preparation method provided by the invention has the advantages of good structural stability and thermal stability, high conductivity, small particle size and uniform distribution, effectively improves the cycle performance and rate capability of the lithium iron phosphate material, and is beneficial to further promoting the industrial application of the material.
5. The invention makes full use of the iron-based catalyst in the preparation process of the carbon tube, omits the procedures of acid washing and impurity removal in the preparation process of the carbon tube, and obviously reduces the comprehensive cost of the lithium iron phosphate/CNTs.
Detailed Description
In order to make the technical problems, technical solutions and advantages to be solved by the present invention clearer, the following detailed description is given with reference to specific embodiments.
Aiming at the existing problems, the invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite anode material, which is characterized in that an iron-based catalyst is used for inducing in-situ growth of carbon nanotubes with good dispersibility, and the carbon nanotubes are used as a raw material to prepare the lithium iron phosphate/carbon nanotube composite anode material.
Example 1
Step one, weighing 30g of iron powder with the median particle size of 0.78um, putting the iron powder into a reaction furnace, and assembling the chemical vapor deposition device. Introducing air in a nitrogen removal device, wherein the gas flow is 300sccm, and heating the reaction furnace to 800 ℃ at the speed of 10 ℃/min. The nitrogen was turned off and ethylene gas was started to flow at a flow rate of 300 sccm. After reacting for 1h at the constant temperature, closing ethylene gas, recovering nitrogen, stopping heating, and cooling along with the furnace to obtain the catalyst/carbon nano tube composite material; the content of iron in the composite material was found to be 83.38 wt% by ICP analysis;
and step two, taking 300ml of 1.5mol/L sulfuric acid solution, adding 10g of catalyst/carbon nano tube composite material, stirring, reacting for 4 hours, adding excessive hydrogen peroxide into the solution, and continuously stirring. 22.37g of ammonium phosphate is weighed and added into the solution, and the pH value of the solution is adjusted to 2.2 by sodium hydroxide solution, and after 1.5h of reaction, a large amount of precipitate can be obtained. Washing and filtering the obtained precipitate, calcining in a protective atmosphere, and removing crystal water to obtain FePO4a/CNTs composite;
step three, FePO is weighed410g of/CNTs composite material and 2.28g of lithium carbonate, grinding for 1.5h, and uniformly mixing the materials;
and step four, putting the obtained powder into an alumina burning boat, pushing the alumina burning boat into the middle of a tube furnace, heating the powder to 720 ℃ at a speed of 5 ℃/min in an argon protective atmosphere, and preserving the heat for 5 hours. Cooling to room temperature along with the furnace to obtain LiFePO4the/CNTs composite anode material comprises 6.58 wt% of carbon nanotubes.
Electrochemical performance tests of button cells assembled by the composite cathode material show that the first discharge specific capacity of the material under 1C multiplying power is 151.2mAh g-1And the capacity circulation retention rate after 100 circles reaches 95.53 percent.
Example 2
Step one, weighing 30g of iron powder with the median particle size of 2.14um, putting the iron powder into a reaction furnace, and assembling the chemical vapor deposition device. Introducing air in an argon removal device, wherein the gas flow is 500sccm, and heating the reaction furnace to 900 ℃ at the speed of 10 ℃/min. The nitrogen was turned off and the methane gas was started to flow at a rate of 500 sccm. After reacting for 1 hour at the constant temperature, closing methane gas and simultaneously recovering argon, stopping heating, cooling along with the furnace to obtain a catalyst/carbon nano tube composite material, and measuring the content of iron in the composite material to be 91.46 wt% by utilizing ICP analysis;
step two, taking 300ml of 1.5mol/L sulfuric acid solution, adding the sulfuric acid solution into a high-pressure reaction kettle, adding 10g of catalyst/carbon nano tube composite material, sealing the reaction kettle and introducing oxygen to ensure that the reaction kettle is enabled to beThe internal oxygen partial pressure is 1200Kpa, the stirring is carried out, the temperature of the reaction kettle is increased to 180 ℃, and the oxygen partial pressure is kept stable in the reaction process. Stopping stirring and heating after 3h, pouring out slurry after the reaction kettle is completely cooled, washing, filtering, calcining in protective atmosphere, and removing crystal water to obtain Fe2O3a/CNTs composite;
step three, weighing Fe2O310g of/CNTs composite material, 13.55g of phosphoric acid (85 wt%), 4.93g of lithium hydroxide monohydrate and 400ml of deionized water are added into a ball milling tank, and ball milling is carried out for 5 hours at 700r/min for uniform mixing;
and step four, carrying out spray drying on the uniformly mixed slurry, setting the air inlet temperature to be 180 ℃, and collecting to obtain mixed powder. Putting the mixed powder into an alumina burning boat, pushing the aluminum oxide burning boat into the middle part of a tube furnace, heating the aluminum oxide burning boat to 700 ℃ at a speed of 10 ℃/min in an argon protective atmosphere, and preserving heat for 5 hours. Cooling to room temperature along with the furnace to obtain LiFePO4The CNTs composite anode material comprises 3.20 wt% of carbon nanotubes.
Electrochemical performance tests of button cells assembled by the composite cathode material show that the first discharge specific capacity of the material under 1C multiplying power is 152.4mAh g-1And the capacity cycle retention rate after 100 circles reaches 94.87%.
Example 3
Step one, weighing an iron-based catalyst (the iron content is 95 wt% and the manganese content is 5 wt%) with the median particle size of 0.85um, putting the catalyst into a reaction furnace, and assembling a chemical vapor deposition device. Introducing air in a nitrogen removal device, wherein the gas flow is 400sccm, and heating the reaction furnace to 900 ℃ at the speed of 5 ℃/min. The nitrogen gas was turned off and the propane gas was started to flow at a flow rate of 400 sccm. After reacting for 1 hour at the constant temperature, closing propane gas and recovering nitrogen, stopping heating, cooling along with the furnace to obtain the catalyst/carbon nano tube composite material, and measuring the content of iron in the composite material to be 86.58 wt% by utilizing ICP analysis;
and step two, taking 300ml of 1.5mol/L sulfuric acid solution, adding 10g of catalyst/carbon nano tube composite material, stirring, reacting for 4 hours, adding excessive hydrogen peroxide into the solution, and continuously stirring.17.83g of ammonium dihydrogen phosphate is weighed and added into the solution, the pH value of the solution is adjusted to 2.0 by sodium hydroxide solution, and a large amount of precipitate can be obtained after 1.5h of reaction. Washing and filtering the obtained precipitate, calcining in protective atmosphere, and removing crystal water to obtain Fe0.95Mn0.05PO4a/CNTs composite;
step three, weighing Fe0.95Mn0.05PO410g of/CNTs composite material and 2.32g of lithium carbonate, and grinding for 1.5h to uniformly grind the materials;
and step four, putting the obtained powder into an alumina burning boat, pushing the alumina burning boat into the middle of a tube furnace, heating the alumina burning boat to 680 ℃ at the speed of 5 ℃/min in the argon protective atmosphere, and preserving the heat for 5 hours. Cooling to room temperature along with the furnace to obtain LiFe0.95Mn0.05PO4the/CNTs composite anode material comprises 5.12 wt% of carbon nanotubes.
Electrochemical performance tests of button cells assembled by the composite cathode material show that the first discharge specific capacity of the material under 1C multiplying power is 151.8mAh g-1And the capacity circulation retention rate after 100 circles reaches 96.26%.
Example 4
Weighing 50g of iron powder with the median particle size of 1.57um, putting the iron powder into a reaction furnace, assembling a chemical vapor deposition device, and introducing argon to remove air in the reaction furnace, wherein the flow of the argon is 300 sccm; heating the reaction furnace to 750 ℃ at the speed of 5 ℃/min, closing argon, starting to introduce methane gas, wherein the gas flow is 70sccm, stopping introducing methane gas after 30min, restarting to introduce argon, preserving the temperature for 30min, and naturally cooling along with the furnace to obtain a catalyst/carbon nano tube composite material, and performing ICP component analysis on the material to obtain the material with the iron content of 84.36 wt%;
step two, weighing 15g of catalyst/carbon nano tube composite material and 0.5g of sodium carboxymethyl cellulose, uniformly mixing, mixing into paste with deionized water, coating the paste on a 7cm multiplied by 7cm titanium net, compacting and drying to obtain the composite anode plate. Weighing ammonium dihydrogen phosphate 22.06g, diluting with deionized water to 500ml, adjusting pH to 2.0 with dilute phosphoric acid, adding 15ml 30% hydrogen peroxide, and assembling electrolysis deviceThe cathode is a titanium plate with the thickness of 7cm multiplied by 7cm, the electrolyte is added, and then direct current is introduced for electrolysis, the electrolysis temperature is 30 ℃, and the current density is 500A/m2And dilute phosphoric acid is used for adjusting the pH value of the electrolyte to be stabilized at about 2.0 in the electrolysis process. After the titanium net substance is completely dissolved, stopping electrifying, washing and filtering the precipitated product for multiple times, and drying and calcining to obtain a precursor/carbon nano tube composite material;
weighing 1.15g of lithium carbonate and 5g of precursor/carbon nanotube composite material, and fully grinding and uniformly mixing;
and step four, putting the precursor/carbon nano tube composite material after grinding and mixing into a tubular resistance furnace, heating to 720 ℃ at a speed of 5 ℃/min in an argon protective atmosphere, preserving the temperature for 5 hours, cooling to room temperature along with the furnace, and obtaining the lithium iron phosphate/carbon nano tube composite anode material, wherein the content of the carbon nano tube in the material is 6.15 wt%.
And assembling the positive electrode material into a button cell to perform electrochemical performance test. The cell was activated at 0.1C rate and tested for cycling performance at 1C rate. Tests show that the first discharge specific capacity of the lithium iron phosphate/carbon nanotube composite positive electrode material under the 1C multiplying power is 153.36mAhg-1And the capacity circulation retention rate after 100 circles reaches 96.74 percent.
Example 5
Step one, weighing 50g of iron-based catalyst with the median particle size of 15.43um (the content of Fe is 95%), putting the catalyst into a tubular resistance furnace, assembling an experimental device and checking the air tightness of the device. Argon gas was introduced into the furnace to exhaust the air in the furnace, and the flow rate of argon gas was 500 sccm. The tubular resistance furnace was heated to 750 ℃ at a heating rate of 10 ℃/min. The furnace temperature was maintained, and the argon flow rate was adjusted to 100 sccm. Introducing cyclohexane at an atomization rate of 10ml/h, stopping introducing a carbon source after 60min, keeping the temperature for 30min, stopping heating, and naturally cooling to room temperature along with the furnace to obtain a catalyst/CNTs composite material;
and step two, carrying out an inductively coupled plasma spectroscopy (ICP-OES) test on the material, and measuring that the content of iron in the composite material is 85.41 wt%. 17.63g of phosphoric acid solution (with the concentration of 85%) is added into 200ml of deionized water, 10g of catalyst/carbon nano tube composite material is added after full stirring, stirring is continued after oxygen is introduced, and after 5 hours of reaction, the pH value of the mixed slurry is adjusted to 2.0 by oxalic acid;
transferring the mixed slurry into a ball mill, adding 5.94g of lithium carbonate, and carrying out ball milling at 300r/min for 3h to uniformly mix the materials; spray drying the mixed slurry at the air inlet temperature of 180 ℃ to obtain a mixed material;
step four, placing the mixed material in a tube furnace, heating to 700 ℃ at a speed of 5 ℃/min in an argon protective atmosphere, preserving heat for 10 hours, and cooling to room temperature along with the furnace to obtain LiFePO4the/CNTs composite anode material.
Grinding and uniformly mixing the lithium ion battery positive electrode material, conductive carbon black and polyvinylidene fluoride (PVDF) according to the mass ratio of 8:1:1, adding a proper amount of N-methyl pyrrolidone (NMP), mixing into slurry, coating the slurry on an aluminum foil, drying for 4 hours in a drying box at 120 ℃, and then cutting into pieces to obtain the lithium ion battery positive electrode piece. And (3) assembling the button cell in a glove box filled with protective gas by taking a metal lithium sheet as a negative electrode. And (3) testing the electrochemical performance of the battery by using a Newware battery testing system, activating at a multiplying power of 0.1C, and testing the cycle performance at a multiplying power of 1C. The LiFePO is found by tests4The first discharge specific capacity of the/CNTs composite anode material under the multiplying power of 1C is 155.6mAhg-1And the capacity circulation retention rate after 100 circles reaches 95.76%.
Example 6
Step one, adopting iron powder with the particle size of 100nm as a catalyst, adopting methane as a carbon source, adopting the flow rate of the methane as 100sccm, adopting argon as a protective atmosphere, adopting the gas flow rate as 1000sccm, adopting the chemical vapor deposition reaction temperature as 800 ℃, and obtaining the iron powder/carbon nano tube composite with the mass fraction of the iron powder of 86.2% through thermogravimetric analysis;
step two, taking 200mL of 2mol/L phosphoric acid solution, adjusting the adding amount of the iron powder/carbon nanotube composite, and controlling the molar ratio of Fe to phosphoric acid to be 1: 2, quantitatively adding KMnO into the solution according to the addition amount of Fe4Controlling the molar ratio of Fe to potassium permanganate to be 5: 3, magnetically stirring the mixture to react for 2 hours, and adjusting the pH of the solution after the reaction to 2, Mn by using ammonia water3(PO4)2、FePO4Precipitating together with the carbon nano tube, filtering and drying the precipitate to obtain a manganese iron phosphate/carbon nano tube precursor;
step three, controlling the molar ratio of lithium to phosphorus to be 1.02, and uniformly grinding the lithium hydroxide and the iron manganese phosphate/carbon nano tube;
and step four, introducing a hydrogen-argon mixer to maintain a reducing atmosphere, wherein hydrogen in the hydrogen-argon mixed gas accounts for 10% of the total volume of the hydrogen-argon mixed gas, sintering the ground product obtained in the step three, wherein the sintering temperature is 800 ℃, the reaction time is 12 hours, and naturally cooling to obtain the lithium manganese iron phosphate/carbon nanotube composite cathode material.
Through tests, the prepared lithium ferric manganese phosphate/carbon nanotube composite positive electrode material is charged and discharged at 0.1C, and the first charging specific capacity is 160mAh g-1The first discharge specific capacity is 154mAh g-1The first charge-discharge efficiency is 96.3 percent, and the 10C specific discharge capacity is 120mAh g-1。
While the foregoing is directed to the preferred embodiment of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (8)

1. A preparation method of a lithium iron phosphate/carbon nanotube composite anode material is characterized by comprising the following steps:
preparing an iron-based catalyst/carbon nanotube composite material from an iron-based catalyst and a gas-phase carbon source by adopting a chemical vapor deposition method;
wherein, in the first step, the content of iron in the iron-based catalyst is 50-100 wt%, and the other is a doping element, wherein the doping element is one or more of Ni, Co, Mn, Mg, Al, Ti, Cr, Zr or W; the particle size of the iron-based catalyst is 10-10000 nm; the iron-based catalyst is one or more of analytically pure grade, industrial grade or other iron-containing waste materials;
step two, the iron-based catalyst/carbon nano tube composite material obtained in the step one is treated by adopting a chemical or electrochemical reaction, and one or more of an iron source, a phosphorus source, a lithium source and a doping element are supplemented in the reaction process to obtain a lithium iron phosphate precursor/carbon nano tube composite material; the chemical or electrochemical reaction is one or more of atmospheric pressure oxidation leaching, pressure oxidation leaching and control electrolysis;
adding a lithium source and a phosphorus source into the lithium iron phosphate precursor/carbon nanotube composite material obtained in the step two, and uniformly mixing to obtain a mixture;
and step four, performing high-temperature solid-phase sintering on the mixture obtained in the step three in a protective atmosphere, and naturally cooling the mixture to room temperature along with the furnace to obtain the lithium iron phosphate/carbon nanotube composite anode material.
2. The method for preparing a lithium iron phosphate/carbon nanotube composite positive electrode material as claimed in claim 1, wherein the carbon source in the first step is one of methane, ethane, propane, ethylene, propylene, acetylene, ethanol, ethylene glycol, propanol, isopropanol, cyclohexane, polyethylene, or polyvinyl alcohol.
3. The preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material as claimed in claim 1, wherein a gas-phase carbon source flow rate in the process of preparing the iron-based catalyst/carbon nanotube composite by the chemical vapor deposition method in the step one is 10-500 sccm, nitrogen or argon is used as a protective atmosphere, a protective gas flow rate is 100-1000 sccm, a chemical vapor deposition reaction temperature is 500-1200 ℃, and a reaction time is 1-10 hours.
4. The preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material as claimed in claim 1, wherein the iron source is one or more of sulfate, nitrate, phosphate, acetate and oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, lithium phosphate and lithium dihydrogen phosphate; the lithium source is one or more of lithium carbonate, lithium phosphate, lithium dihydrogen phosphate, lithium hydroxide and lithium acetate.
5. The method for preparing a lithium iron phosphate/carbon nanotube composite cathode material according to claim 1, wherein the chemical formula of the lithium iron phosphate precursor in the second step is (Fe)xM1-x)yPO4Or (Fe)xM1-x)zO, wherein 0<x≤0.5，2/3≤y≤1，0<z is less than or equal to 1.5, and M is one or more of Ni, Co, Mn, Cu, Zn, Mg, Al, Ti, Cr, Zr, W, Nb, Sn and Mo.
6. The method for preparing a lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein the molar ratio of lithium to iron to the doping element to phosphorus in the mixture obtained in the third step is Li: (Fe + M): p = 0.95-1.10: 0.95-1.05: 0.95 to 1.05; the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium acetate, lithium oxalate or lithium dihydrogen phosphate.
7. The preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material as claimed in claim 1, wherein the temperature of the high-temperature solid phase sintering in the fourth step is 500-900 ℃ and the time is 2-20 h; the protective atmosphere is nitrogen or argon.
8. The method for preparing the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein the content of carbon nanotubes in the lithium iron phosphate/carbon nanotube composite positive electrode material in the fourth step is 0.1-25 wt%, and the content of lithium iron phosphate is 75-99.9 wt%.
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