CN111725516B - LiFePO 4 Preparation method of CNTs composite positive electrode material - Google Patents

LiFePO 4 Preparation method of CNTs composite positive electrode material Download PDF

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CN111725516B
CN111725516B CN202010625885.XA CN202010625885A CN111725516B CN 111725516 B CN111725516 B CN 111725516B CN 202010625885 A CN202010625885 A CN 202010625885A CN 111725516 B CN111725516 B CN 111725516B
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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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Abstract

The invention provides LiFePO 4 The preparation method of the CNTs composite positive electrode material comprises the following steps: (1) preparing an iron-based catalyst/CNTs composite material by CVD; (2) Mixing the catalyst/CNTs composite material with an acidic solution, and taking oxygen as an oxidant to obtain a precursor/CNTs composite material; (3) Mixing the precursor/CNTs composite material, a phosphorus source and a lithium source according to a certain proportion; (4) High-temperature solid phase sintering the mixed material to obtain LiFePO 4 CNTs composite positive electrode material. The method utilizes the pressurized oxidation method to dissolve the iron-based catalyst, accelerates the reaction, and effectively reduces the consumption of acid and alkali and the generation of reaction byproducts; CNTs uniformly dispersed and LiFePO prepared by using the iron-based catalyst 4 The CNTs composite positive electrode material inherits the characteristic; solves the problems of LiFePO 4 The problem of poor conductivity of the anode material improves the electrochemical performance of the material.

Description

LiFePO 4 Preparation method of CNTs composite positive electrode material
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to LiFePO 4 A preparation method of a CNTs composite positive electrode material.
Background
With the continuous prominence of environmental and energy problems, it has been difficult for conventional energy structures to meet the demands of modern society. The development and popularization of new energy related industries are becoming urgent. Lithium ion batteries are one of the most important energy storage devices at present, and are widely applied to the fields of electric automobiles, 3C electronic products, energy storage and the like. In particular, in recent years, the application of lithium ion batteries in the field of vehicle engineering has shown explosive growth, and the development of pure Electric Vehicles (EV) and Hybrid Electric Vehicles (HEV) has also profoundly affected the life style of people. Although the application of lithium ion batteries is very wide, the higher manufacturing cost and potential safety risks limit the further development of lithium ion batteries. The positive electrode material is used as the most important component of the lithium ion battery, the cost of the positive electrode material accounts for about 40% of the total cost of the lithium ion battery, and the performance of the positive electrode material also determines the performance of the lithium ion battery. Currently, the lithium ion battery cathode materials which have been commercially applied mainly include ternary materials, lithium cobaltate, lithium manganate, lithium iron phosphate and the like.
Lithium iron phosphate (LiFePO) 4 ) Has a typical olivine structure and a theoretical specific discharge capacity of 170mAh/g. The lithium iron phosphate positive electrode material has good thermal stability, and the lithium ion battery prepared by the lithium iron phosphate positive electrode material has good safety, and the risk of thermal runaway in the actual use process is small. The lithium iron phosphate anode material belongs to the transformation of a two-phase structure in the charge-discharge process, so that the lithium iron phosphate anode material has strong structural stability and high cycle stability. Meanwhile, the source of raw materials required for preparing the lithium iron phosphate anode material is wide, the price is low, and the lithium iron phosphate anode material is environment-friendly, so that the preparation cost of the lithium iron phosphate anode material is relatively lower than that of other lithium ion battery anode materials. For the above reasons, the lithium iron phosphate material has wide application prospect in the fields of electric automobiles and large-scale energy storage. The lithium iron phosphate material is prepared by reacting ferric sulfate and nitrate as raw materials with phosphoric acid, adjusting the pH value of the solution by alkali liquor, and then mixing and sintering with lithium salt. In this process, a large amount of alkali is consumed, and a large amount of by-products are produced. Therefore, new synthetic methods need to be found to solve these problems. In the disclosures of CN102983328A and CN110615418A, lithium iron phosphate is prepared from iron powder as a raw material, and although the use of alkali and the production of reaction byproducts are avoided, the reaction time of iron powder and an acidic solution is long, the use amount of phosphoric acid is large, and the actual production process of lithium iron phosphate is not facilitated.
Lithium iron phosphate positive electrode materialAnd thus the material is inferior in discharge performance at a large rate. To achieve further application of the lithium iron phosphate material, the material must be modified. The most important modification means of the lithium iron phosphate anode material is to compound with a carbon-based material, so that the electronic conductivity of the lithium iron phosphate anode material is improved, and the electrochemical performance of the material is further improved. Carbon Nanotubes (CNTs) have a one-dimensional structure, can construct a conductive network in a composite material, and are important modified composite materials. However, in the process of compounding lithium iron phosphate and carbon nanotubes, a composite material is uniformly prepared due to the dispersion problem of the carbon nanotubes. Some researchers have proposed methods of growing carbon nanotubes in situ in lithium iron phosphate materials (CN 102427130a, CN101533904 a), but require the introduction of additional catalyst and the catalyst can remain in the final composite, affecting the electrochemical properties of the material. Thus, new methods were developed to prepare LiFePO 4 The CNTs composite positive electrode material is particularly important.
Disclosure of Invention
The invention provides LiFePO 4 The preparation method of the CNTs composite anode material aims to solve the defects and the shortcomings in the background technology.
To achieve the above object, embodiments of the present invention provide a LiFePO 4 The preparation method of the CNTs composite positive electrode material comprises the following steps:
step one: feeding a liquid-phase carbon source into a reaction furnace through spray feeding equipment in a protective atmosphere at a preset temperature by utilizing an iron-based catalyst, and preparing a catalyst/CNTs composite material through CVD;
step two: mixing the catalyst/CNTs composite material with an acidic solution by taking oxygen as an oxidant, reacting at a preset temperature and pressure, filtering and washing for multiple times after the reaction is finished, and drying to obtain a precursor/CNTs composite material;
step three: mixing the precursor/CNTs composite material, an iron source, a phosphorus source and a lithium source according to a preset proportion, transferring the mixture into a ball mill, uniformly mixing for preset time to obtain mixed slurry, and carrying out spray drying on the mixed slurry to obtain a mixed material;
step four: the mixed material is sintered at high temperature and solid phase in protective atmosphere, and is naturally cooled to room temperature along with a furnace to obtain LiFePO 4 CNTs composite positive electrode material.
In the first step, the content of iron in the iron-based catalyst is 50% -100%, and the particle size of the iron-based catalyst is 10nm < d <100000nm.
In the first step, the protective atmosphere is argon or nitrogen, and the gas flow is 10 sccm-5000 sccm; the liquid-phase carbon source is one or more of ethanol, glycol, propanol, isopropanol, cyclohexane, polyethylene or polyvinyl alcohol; the atomization speed of the liquid-phase carbon source is 5 ml/h-100 ml/h.
Wherein in step one, the CVD includes a chemical vapor deposition method or a modified method; the reaction temperature for preparing CNTs is 500-1200 ℃; the time for introducing the atomized liquid carbon source is 10-300 min.
In the second step, the acid solution is one or more of phosphoric acid, sulfuric acid, nitric acid or hydrochloric acid; the molar ratio of the iron-based catalyst to the acid is 1:1 to 5; the solid-liquid ratio of the acid solution to the iron-based catalyst/CNTs composite material is 5 ml/g-50 ml/g; the leaching temperature is 25-225 ℃; the oxygen partial pressure is 20 KPa-3000 KPa; the reaction time is 0.5 h-15 h.
Wherein the chemical formula of the precursor is (Fe x M 1-x ) y O or (Fe) x M 1-x ) z PO 4 Wherein x is more than or equal to 0 and less than or equal to 0.5,0<y is less than or equal to 1.5, z is more than or equal to 2/3 and less than or equal to 1, and M is one or more of Ni, co, mn, cu, zn, mg, al, ti, cr, zr, W, nb, sn or Mo; the molar ratio of the precursor/CNTs composite material, the iron source, the phosphorus source and the lithium source is (Fe+M): p: li=0.95 to 1.1:0.95 to 1.1:0.95 to 1.1.
In the third step, the iron source is one or more of sulfate, nitrate, phosphate, acetate or oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, ammonium phosphate or lithium dihydrogen phosphate; the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate or lithium dihydrogen phosphate.
In the third step, the ball milling and mixing time is 0.5-20 h, and the ball milling rotating speed is 200-3000 r/min; the air inlet temperature of the spray drying is 120-220 ℃.
In the fourth step, the protective atmosphere is argon or nitrogen; the sintering temperature is 600-1000 ℃, and the sintering time is 5-20 h.
The scheme of the invention has the following beneficial effects:
the invention takes iron powder as a catalyst, CNTs grow on the catalyst in situ through CVD, and the catalyst/CNTs composite material is prepared. The mass percent of the iron-based catalyst and CNTs can be controlled by controlling the related parameters in the CVD process, and the CNTs in the composite material have better dispersibility and are the subsequent LiFePO 4 The preparation of the positive electrode material provides an iron source and a carbon source.
The conversion of the catalyst/CNTs composite to the precursor/CNTs composite can be accomplished by atmospheric or pressure oxidative leaching. In the normal pressure oxidation leaching process, iron and carbon primary batteries are formed in the acid solution to accelerate the dissolution of iron powder, so that the acid consumption and the reaction time are reduced. During the pressure oxidation leaching process, fe and acidic solutions in the catalyst/CNTs composites react mainly as follows:
Fe+2H + +1/2O 2 ＝Fe2 + +H 2 O
4Fe 2+ +4H + +O 2 ＝4Fe 3+ +2H 2 O
2Fe 3+ +3H 2 O＝Fe 2 O 3 +6H +
by controlling the partial pressure of oxygen during leaching, iron can be present in divalent and trivalent form, respectively. Different forms of precursors can be prepared according to whether phosphate radical is added or not and the reaction temperature is controlled, for example, phosphate radical is added to prepare phosphate precursor, and oxide precursor can be obtained without adding phosphate radical. Precipitating with dispersed CNTs as nucleation sites, filtering, and washing to obtain precursor +.CNTs composite material. Uniformly mixing the precursor material with a phosphorus source, an iron source and a lithium source in a certain proportion, spray drying and granulating to obtain a precursor material, and carrying out high-temperature solid-phase reaction to obtain LiFePO 4 CNTs composite positive electrode material.
The preparation method provided by the invention avoids the use of alkali, fully utilizes the catalyst iron source in the CNTs preparation process, shortens the CNTs preparation flow, and obviously reduces the production cost. No by-product is produced in the reaction process, and the method is environment-friendly. Meanwhile, the prepared LiFePO 4 The CNTs in the CNTs composite anode material have better dispersivity and no extra catalyst is introduced. Experiments prove that the LiFePO prepared by the method provided by the invention 4 The electrochemical performance of the CNTs composite positive electrode material is excellent.
Drawings
FIG. 1 is a LiFePO of the present invention 4 A flow chart of a preparation method of the CNTs composite anode material.
Detailed Description
In order to make the technical problems, technical solutions and advantages to be solved more apparent, the following detailed description will be given with reference to the accompanying drawings and specific embodiments.
The invention aims at the existing problems and provides LiFePO 4 A preparation method of a CNTs composite positive electrode material.
Embodiment one:
as shown in fig. 1, an embodiment of the present invention provides a LiFePO 4 The preparation method of the CNTs composite positive electrode material comprises the following steps:
step one: 50g of an iron-based catalyst having a median particle diameter of 15.43 μm (content of Fe: 95%) was weighed, placed in a tube resistance furnace, an experimental apparatus was assembled, and the air tightness of the apparatus was checked. Argon is introduced to discharge air in the furnace, and the flow rate of the argon is 500sccm. The tube resistance furnace was warmed to 750 ℃ at a warming rate of 10 ℃/min. The temperature in the furnace was maintained, and the argon flow was adjusted to 100sccm. Introducing cyclohexane at an atomization rate of 10ml/h, stopping introducing a carbon source after 60min, preserving heat for 30min, stopping heating, and naturally cooling to room temperature along with a furnace to obtain a catalyst/CNTs composite material; inductively coupled plasma (ICP-OES) testing is carried out on the material, and the content of iron in the composite material is 85.41wt%;
step two: 17.63g of phosphoric acid solution (85% strength) was added to 200ml of deionized water, and after sufficient stirring, 10g of the catalyst/carbon nanotube composite material was added, and after oxygen was introduced, stirring was continued. After reacting for 5 hours, filtering and washing to obtain mixed slurry;
step three: the mixed slurry was transferred to a ball mill, and 5.94g of lithium carbonate was added thereto, and ball milling was performed at 300r/min for 3 hours to uniformly mix. Spray drying the mixed slurry, wherein the air inlet temperature is 180 ℃, so as to obtain a mixed material;
step four: and (3) placing the mixed material into a tube furnace, heating to 700 ℃ at 5 ℃/min in an argon protective atmosphere, and preserving heat for 10 hours. Cooling to room temperature along with the furnace to obtain LiFePO 4 CNTs composite positive electrode material.
And (3) grinding and mixing the lithium ion battery anode material, the conductive carbon black and polyvinylidene fluoride (PVDF) uniformly in a mass ratio of 8:1:1, adding a proper amount of N-methyl pyrrolidone (NMP) to prepare slurry, coating the slurry on an aluminum foil, drying the slurry in a drying oven at 120 ℃ for 4 hours, and cutting the slurry into pieces to prepare the lithium ion battery anode piece. The button cell was assembled in a glove box filled with a protective gas using a lithium metal sheet as the negative electrode. The electrochemical performance of the cells was tested using a newware cell test system, activated at 0.1C rate, and cycled at 1C rate. Test finds the LiFePO 4 The first discharge specific capacity of the CNTs composite positive electrode material at 1C multiplying power is 155.6mAh g -1 The cycle retention of capacity after 100 cycles reaches 95.76%.
Embodiment two:
step one: 50g of an iron-based catalyst having a median particle diameter of 25.23 μm (content of Fe: 98%) was weighed, placed in a tube resistance furnace, an experimental apparatus was assembled, and the air tightness of the apparatus was checked. Argon is introduced to discharge air in the furnace, and the flow rate of the argon is 1000sccm. The tube resistance furnace was warmed to 950 ℃ at a warming rate of 15 ℃/min. The temperature in the furnace was maintained, and the argon flow was adjusted to 200sccm. Introducing ethanol at an atomization rate of 20ml/h, stopping introducing carbon source after 30min, keeping the temperature for 60min, stopping heating, and naturally cooling to room temperature along with a furnace to obtain a catalyst/CNTs composite material; inductively coupled plasma (ICP-OES) testing is carried out on the material, and the content of iron in the composite material is 87.38wt%;
step two: 48.40g of 95wt% sulfuric acid was weighed, and charged into an autoclave with deionized water to a volume of 400 ml. Weighing 20g of Fe/CNTs composite material, adding the composite material into a high-pressure reaction kettle, and sealing the high-pressure reaction kettle after preliminary reaction for 10 min. Slowly introducing oxygen into the autoclave, controlling the oxygen partial pressure to 1000Kpa, simultaneously turning on a heating power supply, and starting stirring when the temperature is 170 ℃. As the reaction proceeds, oxygen is continuously consumed, and the oxygen pressure is kept stable by pressurization according to the indication of the oxygen pressure gauge. After 2h of reaction, stopping heating and stirring, lifting the autoclave from the furnace body, placing, naturally cooling, and opening a release valve. Removing the slurry in the autoclave, filtering and washing for multiple times, and drying the filter cake to obtain Fe 2 O 3 CNTs composite; ICP-OES test was performed to measure Fe 2 O 3 The Fe content of the CNTs composite material is 62.47wt%;
step three: weighing Fe 2 O 3 10g of CNTs composite material, 12.89g of phosphoric acid (85 wt%) and 2.67g of lithium hydroxide, 300ml of deionized water. Adding the materials into a ball milling tank, and ball milling for 2 hours at 500r/min to uniformly mix the materials. Spray drying the mixed slurry, wherein the air inlet temperature is 150 ℃, so as to obtain a mixed material;
step four: the mixed material is placed in a tube furnace, and is heated to 750 ℃ at 5 ℃/min for 6h under the protection of argon. Cooling to room temperature along with the furnace to obtain LiFePO 4 CNTs composite positive electrode material.
And (3) grinding and mixing the lithium ion battery anode material, the conductive carbon black and polyvinylidene fluoride (PVDF) uniformly in a mass ratio of 8:1:1, adding a proper amount of N-methyl pyrrolidone (NMP) to prepare slurry, coating the slurry on an aluminum foil, drying the slurry in a drying oven at 120 ℃ for 4 hours, and cutting the slurry into pieces to prepare the lithium ion battery anode piece. The button cell was assembled in a glove box filled with a protective gas using a lithium metal sheet as the negative electrode. Electrochemical performance of the cells was tested using a newware cell test system, activated at 0.1C rate, cycled at 1C rateRing performance test. Test finds the LiFePO 4 The first discharge specific capacity of the CNTs composite positive electrode material at 1C multiplying power is 156.7mAh g -1 The cycle retention of capacity after 100 cycles reaches 97.38%.
Embodiment III:
step one: 50g of iron powder with a median particle diameter of 0.83um was weighed, the catalyst was put into a tube resistance furnace, an experimental apparatus was assembled, and the air tightness of the apparatus was checked. Argon is introduced to discharge air in the furnace, and the flow rate of the argon is 200sccm. The tube resistance furnace was warmed to 750 ℃ at a warming rate of 10 ℃/min. The temperature in the furnace was maintained, and the argon flow was adjusted to 50sccm. Introducing polyethylene at an atomization rate of 30ml/h, stopping introducing a carbon source after 30min, keeping the temperature for 60min, stopping heating, naturally cooling to room temperature along with a furnace, and taking out the sediment on the alumina flake to obtain the Fe/CNTs composite material; the material was subjected to inductively coupled plasma spectroscopy (ICP-OES) to determine that the iron content of the composite material was 84.37wt%;
step two: adding sulfuric acid-phosphoric acid mixed acid, fixing the volume to 300ml by deionized water, and adding into a high-pressure reaction kettle. Weighing 20g of Fe/CNTs composite material, adding the composite material into a high-pressure reaction kettle, and sealing the high-pressure reaction kettle after preliminary reaction for 10 min. Slowly introducing nitrogen into the autoclave, controlling the oxygen partial pressure to 1500Kpa, simultaneously turning on a heating power supply, and starting stirring when the temperature is heated to 200 ℃. As the reaction proceeds, oxygen is continuously consumed, and the oxygen pressure is kept stable by pressurization according to the indication of the oxygen pressure gauge. After 1h of reaction, stopping heating and stirring, lifting the autoclave from the furnace body, placing, naturally cooling, and opening a release valve. Removing the slurry in the autoclave, filtering and washing for multiple times, and drying the filter cake to obtain Fe 3 (PO 4 ) 2 CNTs composite;
step three: weighing Fe 3 (PO 4 ) 2 CNTs composite material, lithium oxalate and deionized water 300ml. Adding the materials into a ball milling tank, and carrying out ball milling for 3 hours at 300r/min to uniformly mix the materials. Spray drying the mixed slurry, wherein the air inlet temperature is 200 ℃, so as to obtain a mixed material;
step four: placing the mixed material into a tube furnace, and heating to 700 ℃ at 10 ℃/min in an argon protective atmosphereAnd (5) preserving heat for 8 hours to bake. Cooling to room temperature along with the furnace to obtain LiFePO 4 CNTs composite positive electrode material.
And (3) grinding and mixing the lithium ion battery anode material, the conductive carbon black and polyvinylidene fluoride (PVDF) uniformly in a mass ratio of 8:1:1, adding a proper amount of N-methyl pyrrolidone (NMP) to prepare slurry, coating the slurry on an aluminum foil, drying the slurry in a drying oven at 120 ℃ for 4 hours, and cutting the slurry into pieces to prepare the lithium ion battery anode piece. The button cell was assembled in a glove box filled with a protective gas using a lithium metal sheet as the negative electrode. The electrochemical performance of the cells was tested using a newware cell test system, activated at 0.1C rate, and cycled at 1C rate. Test finds the LiFePO 4 The first discharge specific capacity of the CNTs composite positive electrode material at 1C multiplying power is 153.4mAh g -1 The cycle retention of capacity after 100 cycles reaches 96.26%.
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the present invention.

Claims (9)

1. LiFePO 4 The preparation method of the CNTs composite positive electrode material is characterized by comprising the following steps:
step one: feeding a liquid-phase carbon source into a reaction furnace through spray feeding equipment in a protective atmosphere at a preset temperature by utilizing an iron-based catalyst, and preparing a catalyst/CNTs composite material through CVD; the preset temperature is 500-1200 ℃; the protective atmosphere is argon or nitrogen; the iron content in the iron-based catalyst is 50% -100%;
step two: mixing the catalyst/CNTs composite material with an acidic solution by taking oxygen as an oxidant, reacting in a normal-pressure or pressurized oxidation leaching mode at a preset temperature and pressure, filtering and washing for multiple times after the reaction is finished, and drying to obtain a precursor/CNTs composite material; the leaching temperature is 25-225 ℃; the oxygen partial pressure is 20 KPa-3000 KPa;
step three: mixing the precursor/CNTs composite material, an iron source, a phosphorus source and a lithium source according to a preset proportion, transferring the mixture into a ball mill, uniformly mixing for preset time to obtain mixed slurry, and carrying out spray drying on the mixed slurry to obtain a mixed material;
step four: the mixed material is sintered at high temperature and solid phase in protective atmosphere, and is naturally cooled to room temperature along with a furnace to obtain LiFePO 4 CNTs composite positive electrode material.
2. LiFePO according to claim 1 4 The preparation method of the CNTs composite positive electrode material is characterized in that in the first step, the content of iron in the iron-based catalyst is 50-100%, and the particle size of the iron-based catalyst is 10nm < d <100000nm.
3. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the first step, the protective atmosphere is argon or nitrogen, and the gas flow is 10 sccm-5000 sccm; the liquid-phase carbon source is one or more of ethanol, glycol, propanol, isopropanol, cyclohexane, polyethylene or polyvinyl alcohol; the atomization speed of the liquid-phase carbon source is 5 ml/h-100 ml/h.
4. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the first step, the CVD comprises a chemical vapor deposition method, and the reaction temperature for preparing CNTs is 500-1200 ℃; the time for introducing the atomized liquid carbon source is 10 min-300 min.
5. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the second step, the acidic solution is one or more of phosphoric acid, sulfuric acid, nitric acid or hydrochloric acid; the molar ratio of the iron-based catalyst to the acid is 1:1-5; the solid-liquid ratio of the acid solution to the iron-based catalyst/CNTs composite material is 5 ml/g-50 ml/g; the leaching temperature is 25-225 ℃; the oxygen partial pressure is 20 KPa-3000 KPa; the reaction time was 0.5h～15h。
6. LiFePO according to claim 1 4 The preparation method of the CNTs composite positive electrode material is characterized in that the chemical formula of the precursor is (Fe x M 1-x ) y O or (Fe) x M 1-x ) z PO 4 Wherein x is more than 0 and less than or equal to 0.5, y is more than 0 and less than or equal to 1.5, z is more than or equal to 2/3 and less than or equal to 1, and M is one or more than one of Ni, co, mn, cu, zn, mg, al, ti, cr, zr, W, nb, sn and Mo; the molar ratio of the iron source, the phosphorus source and the lithium source is 0.95-1.1:0.95-1.1.
7. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the third step, the iron source is one or more of sulfate, nitrate, phosphate, acetate or oxide of divalent or trivalent iron; the phosphorus source is one or more of phosphoric acid, monoammonium phosphate, ammonium phosphate or lithium dihydrogen phosphate; the lithium source is one or more of lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate or lithium dihydrogen phosphate.
8. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the third step, the time of ball milling and mixing is 0.5-20 h, and the ball milling rotating speed is 200-3000 r/min; the air inlet temperature of the spray drying is 120-220 ℃.
9. LiFePO according to claim 1 4 The preparation method of the CNTs composite anode material is characterized in that in the fourth step, the protective atmosphere is argon or nitrogen; the sintering temperature is 600-1000 ℃, and the sintering time is 5-20 h.
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