CN111740113B - 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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CN111740113B
CN111740113B CN202010624197.1A CN202010624197A CN111740113B CN 111740113 B CN111740113 B CN 111740113B CN 202010624197 A CN202010624197 A CN 202010624197A CN 111740113 B CN111740113 B CN 111740113B
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lithium
carbon nanotube
nanotube composite
iron
iron phosphate
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CN111740113A (en
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颜果春
王接喜
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

The invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite anode material, which comprises the following steps: (1) preparing an iron-based catalyst/carbon nano tube composite material by a chemical vapor deposition method; (2) mixing the catalyst/carbon nano tube composite material with an acidic solution, adding a certain amount of phosphorus source, iron source and hydrogen peroxide to obtain a mixed solution, stirring and reacting for a certain time, regulating the pH value with the alkaline solution to obtain a precipitate, and filtering, washing and drying for multiple times to obtain a precursor/carbon nano tube composite material; (3) mixing the precursor/carbon nano tube composite material and a lithium source according to a certain proportion; (4) and sintering the mixed material at high temperature to obtain the lithium iron phosphate/carbon nanotube composite anode material. The carbon nanotubes in the lithium iron phosphate/carbon nanotube composite cathode material prepared by the invention form a good conductive network, so that the problem of poor conductivity of the lithium iron phosphate cathode material is solved, and the electrochemical performance of the material is improved.

Description

Preparation method of lithium iron phosphate/carbon nanotube composite positive electrode material
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to a preparation method of a lithium iron phosphate/carbon nanotube composite anode material.
Background
Since the commercialization of lithium ion batteries, lithium ion batteries have become the most interesting secondary batteries due to their advantages of higher energy density, higher operating voltage, longer cycle life, and environmental friendliness. The lithium ion battery is widely applied to the fields of portable electronic products, power batteries, large-scale energy storage and the like, and the research on the lithium ion battery is increasingly deepened along with the continuous improvement of the performance requirements of various fields on the lithium ion battery. The lithium ion battery mainly comprises a positive electrode, a negative electrode, a diaphragm, electrolyte, a shell and the like, wherein the positive electrode material has the most obvious influence on the cost and the performance of the lithium ion battery. Currently, the commercial lithium ion battery anode materials mainly include lithium cobaltate, ternary materials, lithium manganate, lithium iron phosphate and the like. Since the requirements for the cost and safety of lithium ion batteries in various fields are further increased, lithium iron phosphate is one of the most mainstream positive electrode materials.
Although the lithium iron phosphate positive electrode material has high safety, high cycling stability and low preparation cost, the lithium iron phosphate material is generally required to be modified due to low conductivity and low lithium ion diffusion rate of the material. Among them, the composite modification with carbon materials is one of the most significant methods at present. The carbon nano tube has good electronic conductivity, and the one-dimensional structure of the carbon nano tube can form a good conductive network in the anode material, so that the electrochemical performance of the anode material can be effectively improved. Generally, when preparing a lithium iron phosphate/carbon nanotube composite material, a lithium iron phosphate material and a carbon nanotube are required to be prepared respectively, and lithium iron phosphate is then compounded with the dispersed carbon nanotube. However, carbon nanotubes have poor dispersibility due to their own characteristics, and it is difficult to prepare a uniform composite material. In the disclosure of CN102427130A and CN101533904A, although the composite material of carbon nanotubes and lithium iron phosphate is generated in situ by chemical vapor deposition, an additional catalyst is added during the preparation of the material and is difficult to remove during subsequent processing. Therefore, the method has important significance for developing the preparation method of the lithium iron phosphate/carbon nanotube composite anode material with environmental friendliness and excellent performance.
Disclosure of Invention
The invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite positive electrode material, and aims to overcome the defects in the background technology.
In order to achieve the above object, an embodiment of the present invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite positive electrode material, including the following steps:
the method comprises the following steps: preparing a catalyst/carbon nano tube composite material by using an iron-based catalyst and carbon-containing gas as a raw material in a protective atmosphere at a preset temperature by using a chemical vapor deposition method;
step two: mixing the catalyst/carbon nano tube composite material with an acidic solution, adding a predetermined amount of phosphorus source, iron source and hydrogen peroxide to obtain a mixed solution, stirring and reacting for a predetermined time, adjusting the pH value with the alkaline solution to obtain a precipitate, filtering and washing for multiple times, drying, and then calcining at a high temperature in a protective atmosphere to obtain a precursor/carbon nano tube composite material;
step three: mixing the precursor/carbon nanotube composite material with a predetermined amount of lithium source, carrying out ball milling by using water or ethanol as a dispersing agent, and carrying out spray drying on the obtained slurry to obtain a mixed material;
step four: and sintering the mixed material at high temperature in a protective atmosphere to obtain the lithium iron phosphate/carbon nanotube composite anode material.
Wherein in the first step, the iron content in the iron-based catalyst is 50 wt% -100 wt%; the particle size of the iron-based catalyst is 10nm < d <100000 nm; other elements in the iron-based catalyst are one or more of Ni, Co, Mn, Mg, Al, Ti, Zr or W.
In the first step, the carbon-containing gas is one or more of methane, ethane, propane, ethylene, propylene, acetylene, ethanol, natural gas or liquefied petroleum gas; in the first step, the reaction temperature is 500-1000 ℃; the protective atmosphere is argon or nitrogen, and the gas flow is 10 sccm-1000 sccm; the flow rate of the carbon-containing gas is 10sccm to 500 sccm.
Wherein in the second step, the acidic solution is phosphoric acid and sulfuric acidOne of hydrochloric acid or nitric acid; the molar ratio of the iron-based catalyst to the acidic solution is 1: 1-5; the liquid-solid ratio of the acidic solution to the iron-based catalyst/carbon nanotube composite material is 5 ml/g-50 ml/g; fe in the mixed solutionxM1-xAnd the molar ratio of P is 1: 0.95 to 1.05.
In the second step, the iron source is one or more of phosphate, acetate, chloride, sulfate, nitrate or oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate or lithium dihydrogen phosphate.
In the second step, the alkaline solution is sodium hydroxide or ammonia water; the adjusted pH value is 0.5-3.0; the high-temperature calcination temperature is 200-600 ℃, and the high-temperature calcination time is 0.5-15 h.
Wherein, in the second step, the chemical formula of the precursor is (Fe)xM1-x)yPO4Wherein 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 1.05, and M is one or more of Ni, Co, Mn, Cu, Zn, Mg, Al, Ti, Cr, Zr, W, Nb, Sn or Mo.
In the third step, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate or lithium dihydrogen phosphate; fexM1-xMolar ratio to Li of 1: 0.95 to 1.05; the ball milling time is 0.5 h-10 h; the rotating speed of the ball mill is 200 r/min-2000 r/min; the air inlet temperature of the spray drying is 140-220 ℃.
In the fourth step, the protective atmosphere is argon or nitrogen; the roasting temperature is 600-1000 ℃ during high-temperature sintering, and the roasting time is 5-20 h; the content of the carbon nano tube in the lithium iron phosphate/carbon nano tube composite anode material is 1-30 wt%.
The scheme of the invention has the following beneficial effects:
the invention utilizes the iron-based catalyst to prepare the catalyst/carbon nano tube composite material in situ by a vapor deposition method, and the carbon nano tube in the composite material has controllable appearance and good dispersibility. The iron in the catalyst is used as the source of the iron in the lithium iron phosphate material, so that the secondary separation of the catalyst and the carbon nano tube is avoided. In acidic solutions, iron and carbon can form micro-batteries, forming soluble iron anodes, accelerating the chemical reactions. The hydrogen peroxide is used as an oxidant to oxidize ferrous ions into ferric ions, and the ferric ions have a catalytic effect on the decomposition of the hydrogen peroxide, so that the overall reaction speed is improved. In the process of generating the precursor, the carbon nano tube can provide a large number of nucleation sites, and the generated precipitate is more prone to form crystal nuclei rather than growing up, so that the particle size of the finally prepared lithium iron phosphate material is controlled. The small particle size material has a shorter lithium ion diffusion distance, and the material can exhibit better electrochemical performance. In the lithium iron phosphate/carbon nanotube composite anode material, the carbon nanotubes can form a good conductive network framework, so that the transmission of electrons among lithium iron phosphate particles is improved, and the electrochemical performance of the material is further improved. Experiments prove that the lithium iron phosphate/carbon nanotube composite anode material prepared by the invention has good electrochemical performance.
Drawings
Fig. 1 is a flow chart of a preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantages of the present invention more apparent, the following detailed description is given with reference to the accompanying drawings and specific embodiments.
Aiming at the existing problems, the invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite anode material
The first embodiment is as follows:
as shown in fig. 1, an embodiment of the present invention provides a preparation method of a lithium iron phosphate/carbon nanotube composite positive electrode material, including the following steps:
the method comprises the following steps: weighing 50g of iron-based catalyst (the iron content is 98 wt%) with the median particle size of 0.82um, putting the iron-based catalyst into a tubular resistance furnace, assembling an experimental device and checking the air tightness of the device; introducing nitrogen to remove air in the device, wherein the flow rate of the nitrogen is 300sccm, and heating the tubular resistance furnace to 750 ℃ at the speed of 15 ℃/min. When the temperature in the furnace reaches the set temperature, the nitrogen is closed, and simultaneously methane is introduced, wherein the gas flow is 100 sccm. And (3) stopping introducing the carbon source gas after 25min of introducing ethylene, starting introducing nitrogen, preserving the heat for 30min, naturally cooling to room temperature, and taking out the iron powder/carbon nano tube composite material. Performing an inductively coupled plasma spectroscopy (ICP-OES) test on the material to obtain that the content of iron in the composite material is 88.78 wt%;
step two: 67.00g of 38 wt% hydrochloric acid was weighed out and made up to 400ml with deionized water. Weighing 20g of catalyst/carbon nanotube composite material, adding the catalyst/carbon nanotube composite material into a hydrochloric acid solution, and stirring for reaction for 2 hours to completely dissolve the catalyst; weighing 36.75g of ammonium dihydrogen phosphate, using deionized water to fix the volume to 200ml, adding an ammonium dihydrogen phosphate solution into the slurry, adding excessive hydrogen peroxide, mixing the slurry with sodium hydroxide to obtain a pH value of 2.0, and continuously stirring for 8 hours to obtain a large amount of precipitate. Filtering and washing the precipitate for 3 times, drying the filter cake, and then preserving heat for 4 hours in an argon atmosphere at 600 ℃ to obtain a precursor/carbon nano tube composite material without crystal water;
step three: weighing 10g of precursor/carbon nanotube composite material, 2.39g of lithium carbonate and 400ml of deionized water. Adding the mixture into a ball milling tank, and carrying out ball milling for 1h at 1000r/min to uniformly mix the materials; spray drying the uniformly mixed slurry, setting the air inlet temperature at 170 ℃, and collecting to obtain a mixed material;
step four: and (3) placing the mixed material in a tube furnace, heating to 700 ℃ at a speed of 5 ℃/min in an argon protective atmosphere, and preserving heat for 5h for roasting. And cooling the lithium iron phosphate/carbon nano tube to room temperature along with the furnace to obtain the lithium iron phosphate/carbon nano tube composite anode material.
Mixing the lithium iron phosphate/carbon nanotube composite anode material with conductive carbon black and PVDF according to the proportion of 8: 1: 1, preparing a positive plate, taking metal lithium as a counter electrode, and assembling the button cell in a glove box. And testing the assembled 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. 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 154.64mAh g-1And the capacity circulation retention rate after 100 circles reaches 96.27%.
Example two:
the method comprises the following steps: 50g of a catalyst having a median particle size of 0.82um (iron content 98 wt%) was weighed, placed in a tubular resistance furnace, the experimental setup was assembled and the air tightness of the setup was checked. Introducing nitrogen to remove air in the device, wherein the flow rate of the nitrogen is 300sccm, and heating the tubular resistance furnace to 750 ℃ at the speed of 15 ℃/min. When the temperature in the furnace reaches the set temperature, the nitrogen is closed, and simultaneously methane is introduced, wherein the gas flow is 100 sccm. Stopping introducing carbon source gas after introducing ethylene for 25min, starting introducing nitrogen, preserving the heat for 30min, naturally cooling to room temperature, and taking out the iron powder/carbon nanotube composite material; performing an inductively coupled plasma spectroscopy (ICP-OES) test on the material to obtain that the content of iron in the composite material is 88.78 wt%;
step two: 67.00g of 38 wt% hydrochloric acid was weighed out and made up to 400ml with deionized water. And (3) weighing 20g of the catalyst/carbon nano tube composite material, adding the catalyst/carbon nano tube composite material into a hydrochloric acid solution, and stirring for reaction for 2 hours to completely dissolve the catalyst. Weighing 36.75g of ammonium dihydrogen phosphate, using deionized water to fix the volume to 200ml, adding an ammonium dihydrogen phosphate solution into the slurry, adding excessive hydrogen peroxide, mixing the slurry with sodium hydroxide to obtain a pH value of 2.0, and continuously stirring for 8 hours to obtain a large amount of precipitate. Filtering and washing the precipitate for 3 times, drying the filter cake, and then preserving heat for 4 hours in an argon atmosphere at 600 ℃ to obtain a precursor/carbon nano tube composite material without crystal water;
step three: weighing 10g of precursor/carbon nanotube composite material, 2.66g of lithium hydroxide monohydrate and 400ml of deionized water. Adding the mixture into a ball milling tank, and carrying out ball milling for 5 hours at a speed of 500r/min to uniformly mix the materials; spray drying the mixed slurry at the air inlet temperature of 180 ℃ to obtain a mixed material;
step four: and (3) placing the mixed material in a tubular furnace, heating to 650 ℃ at the speed of 5 ℃/min in a nitrogen protective atmosphere, and keeping the temperature for 6h for roasting. And cooling the lithium iron phosphate/carbon nano tube to room temperature along with the furnace to obtain the lithium iron phosphate/carbon nano tube composite anode material.
And assembling the lithium iron phosphate/carbon nanotube composite anode material into a button cell, and carrying out electrochemical performance test. Tests show that the lithium iron phosphate/carbon nano tube compositeThe first discharge specific capacity of the mixed anode material under the multiplying power of 1C is 153.7mAh g-1And the capacity circulation retention rate after 100 circles reaches 94.43%.
Example three:
the method comprises the following steps: 50g of a catalyst having a median particle size of 2.54um (iron content 95 wt%) was weighed, placed in a tubular resistance furnace, the experimental setup was assembled and the air tightness of the setup was checked. Introducing argon to remove air in the device, wherein the flow of the argon is 500sccm, and heating the tubular resistance furnace to 800 ℃ at the speed of 15 ℃/min. When the temperature in the furnace reaches the set temperature, argon is closed, and acetylene is introduced at the same time, wherein the gas flow is 30 sccm. And (3) stopping introducing the carbon source gas after 15min of introducing ethylene, starting introducing argon, preserving the heat for 20min, naturally cooling to room temperature, and taking out the iron powder/carbon nano tube composite material. Performing inductively coupled plasma spectroscopy (ICP-OES) test on the material to obtain that the content of iron in the composite material is 84.37 wt%;
step two: 58.00g of 68 wt% nitric acid was weighed and made up to 500ml with deionized water. And (3) weighing 20g of the catalyst/carbon nano tube composite material, adding the catalyst/carbon nano tube composite material into a nitric acid solution, and stirring for reaction for 2 hours to completely dissolve the catalyst. Weighing 34.93g of ammonium dihydrogen phosphate, using deionized water to fix the volume to 200ml, adding an ammonium dihydrogen phosphate solution into the slurry, adding excessive hydrogen peroxide, mixing the slurry with sodium hydroxide to obtain a pH value of 2.2, and continuously stirring for 6 hours to obtain a large amount of precipitate. Filtering and washing the precipitate for 3 times, drying the filter cake, and then preserving heat for 4 hours in an argon atmosphere at 600 ℃ to obtain a precursor/carbon nano tube composite material without crystal water;
step three: weighing 10g of precursor/carbon nanotube composite material, 5.95g of lithium oxalate and 300ml of deionized water. Ball milling at 400r/min for 4h for uniform mixing; spray drying the mixed slurry at the air inlet temperature of 200 ℃ to obtain a mixed material;
step four: and (3) placing the mixed material in a tube furnace, heating to 720 ℃ at a speed of 10 ℃/min in an argon protective atmosphere, and preserving heat for 8h for roasting. And cooling the lithium iron phosphate/carbon nano tube to room temperature along with the furnace to obtain the lithium iron phosphate/carbon nano tube composite anode material.
The lithium iron phosphate/carbon nano tube composite anode materialAnd assembling the button cell by using the material, and performing electrochemical performance test. 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 151.8mAh g-1And the capacity circulation retention rate after 100 circles reaches 92.68%.
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 (9)

1. A preparation method of a lithium iron phosphate/carbon nanotube composite anode material is characterized by comprising the following steps:
the method comprises the following steps: preparing a catalyst/carbon nano tube composite material by using an iron-based catalyst and carbon-containing gas as a raw material in a protective atmosphere at a preset temperature by using a chemical vapor deposition method;
the iron content of the iron-based catalyst is 50 wt% -100 wt%, and other elements M in the iron-based catalyst are one or more of Ni, Co, Mn, Mg, Al, Ti, Zr or W;
step two: mixing the catalyst/carbon nano tube composite material with an acidic solution, adding a predetermined amount of phosphorus source, iron source and hydrogen peroxide to obtain a mixed solution, stirring and reacting for a predetermined time, adjusting the pH value with the alkaline solution to obtain a precipitate, filtering and washing for multiple times, drying, and then calcining at a high temperature in a protective atmosphere to obtain a precursor/carbon nano tube composite material;
step three: mixing the precursor/carbon nanotube composite material with a predetermined amount of lithium source, carrying out ball milling by using water or ethanol as a dispersing agent, and carrying out spray drying on the obtained slurry to obtain a mixed material;
step four: and sintering the mixed material at high temperature in a protective atmosphere 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 according to claim 1, wherein in the first step, the particle size of the iron-based catalyst is 10nm < d <100000 nm.
3. The preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the first step, the carbon-containing gas is one or more of methane, ethane, propane, ethylene, propylene, acetylene, ethanol, natural gas or liquefied petroleum gas; in the first step, the reaction temperature is 500-1000 ℃; the protective atmosphere is argon or nitrogen, and the gas flow is 10 sccm-1000 sccm; the flow rate of the carbon-containing gas is 10sccm to 500 sccm.
4. The method for preparing the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the second step, the acidic solution is one of phosphoric acid, sulfuric acid, hydrochloric acid or nitric acid; the molar ratio of the iron-based catalyst to the acidic solution is 1: 1-5; the liquid-solid ratio of the acidic solution to the iron-based catalyst/carbon nanotube composite material is 5 ml/g-50 ml/g; the iron-based catalyst FexM1-xAnd the molar ratio of P is 1: 0.95 to 1.05.
5. The preparation method of the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the second step, the iron source is one or more of phosphate, acetate, chloride, sulfate, nitrate or oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, ammonium monohydrogen phosphate, ammonium dihydrogen phosphate, ammonium phosphate or lithium dihydrogen phosphate.
6. The method for preparing the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the second step, the alkaline solution is sodium hydroxide or ammonia water; the adjusted pH value is 0.5-3.0; the high-temperature calcination temperature is 200-600 ℃, and the high-temperature calcination time is 0.5-15 h.
7. According to claim 1The preparation method of the lithium iron phosphate/carbon nanotube composite cathode material is characterized in that in the second step, the chemical formula of the precursor is (Fe)xM1-x)yPO4Wherein x is more than 0 and less than or equal to 0.5, y is more than or equal to 2/3 and less than or equal to 1.05, and M is one or more of Mn, Mg, Al or Ti.
8. The method for preparing the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the third step, the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate or lithium dihydrogen phosphate; the mol ratio of Li to the iron-based catalyst in the first step is 0.95-1.05: 1; the ball milling time is 0.5 h-10 h; the rotation speed of the ball milling is 200 r/min-2000 r/min; the air inlet temperature of the spray drying is 140-220 ℃.
9. The method for preparing the lithium iron phosphate/carbon nanotube composite positive electrode material according to claim 1, wherein in the fourth step, the protective atmosphere is argon or nitrogen; the roasting temperature is 600-1000 ℃ during high-temperature sintering, and the roasting time is 5-20 h; the content of the carbon nano tube in the lithium iron phosphate/carbon nano tube composite anode material is 1-30 wt%.
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