CN113651303A - Preparation method of nano flaky iron phosphate and LiFePO prepared by using same4Positive electrode active material/C - Google Patents
Preparation method of nano flaky iron phosphate and LiFePO prepared by using same4Positive electrode active material/C Download PDFInfo
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Abstract
The invention discloses a preparation method of nano flaky iron phosphate and LiFePO prepared by applying the same4a/C positive electrode active material comprising the steps of: 1) adding ferrous oxide containing ferrous iron into a phosphoric acid solution, then adding an oxidant, and carrying out heat preservation reaction to obtain dihydrate ferric phosphate slurry; 2) dihydrate ferric phosphateWashing, filtering, drying and roasting the slurry to obtain nano flaky iron phosphate; 3) mixing and wet-milling nano flaky iron phosphate, a lithium source and an organic carbon source, mixing lithium and coating carbon, and drying to obtain a precursor; 4) sintering the precursor under protective atmosphere to obtain LiFePO4a/C positive electrode active material. According to the invention, the nano flaky ferric phosphate is prepared by a solid-liquid phase conversion preparation method, and the morphological distribution of the product lithium iron phosphate is improved by the flaky ferric phosphate, so that the electrochemical performance and the physical performance of the final lithium iron phosphate are improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery anode materials, and particularly relates to a preparation method of nano flaky iron phosphate and LiFePO prepared by applying the same4a/C positive electrode active material.
Background
With the irreversible consumption of fossil energy, new energy is becoming an indispensable part of people's life, and among them, the application of lithium ion batteries is the most common. The lithium iron phosphate anode material has good electrochemical performance, stable charging and discharging platform, no toxicity, no pollution, long cycle life and good safety performance, and can be used in high-temperature environment. Therefore, those in the art have conducted extensive studies on lithium iron phosphate positive electrode materials. The lithium iron phosphate anode material has the defects of large tap density fluctuation, low compaction density, poor electronic conductivity, low lithium ion diffusion rate and the like, and the ferric phosphate is used as a precursor mainly used for synthesizing the lithium iron phosphate anode material, so that the morphological characteristics and the electrochemical performance of the lithium iron phosphate material are determined to a great extent. Therefore, it is a trend in the field to improve various properties of lithium iron phosphate by controlling iron phosphate.
At present, soluble ferrous sulfate is generally used as a raw material in the iron phosphate preparation process, an iron phosphate precursor with a certain aggregate is obtained through a coprecipitation process, metal salts containing anions (sulfate radicals, nitrate radicals and the like) are required to be introduced in the preparation process, and the metal salts are required to be washed for multiple times, so that waste water is required to be treated, and the process cost is increased. Therefore, it is necessary to develop a synthesis technique with high atom utilization and low environmental load.
Disclosure of Invention
In order to solve the problems in the prior art, the invention aims to provide a preparation method of nano flaky iron phosphate and LiFePO prepared by applying the same4the/C positive electrode active material is prepared by a solid-liquid phase conversion preparation method to prepare nano flaky ferric phosphate, and the flaky ferric phosphate is used for improving the shape distribution of the product lithium iron phosphate, so that the electrochemical performance and the physical performance of the final lithium iron phosphate are improved.
A preparation method of nano flaky iron phosphate comprises the following steps:
1) adding ferrous oxide containing ferrous iron into a phosphoric acid solution, then adding an oxidant, and carrying out heat preservation reaction to obtain dihydrate ferric phosphate slurry;
2) washing, filtering, drying and roasting the dihydrate ferric phosphate slurry to obtain the nano flaky ferric phosphate.
Preferably, in the step 1), the concentration of the phosphoric acid solution is 1-2 mol/L.
Preferably, in the step 1), the iron oxide is at least one of ferroferric oxide and ferrous oxide, the ferroferric oxide is magnetite beneficiated powder or chemically pure powder, the purity of the magnetite is more than 99%, and the purity of the ferrous oxide is more than 99%; the molar ratio of phosphorus in the phosphoric acid solution to iron in the iron oxide is 2-3: 1.
Preferably, in step 1), the oxidant is 30 wt% H2O2The addition amount is 1-2 times of the theoretical amount of the ferrous iron in the iron oxide.
Preferably, in the step 1), the reaction is carried out at a temperature of 60-90 ℃ for 0.5-5h and a pH value of 1-2. In the invention, the whole preparation process of the ferric phosphate dihydrate is carried out under heating, and iron phosphorus fully reacts under the stirring action to form uniform white thick iron phosphorus slurry.
Preferably, in the step 2), the roasting temperature is 500-600 ℃, and the time is 2-6 h. According to the invention, the ferric phosphate dihydrate is sintered at a high temperature, and crystal water in the ferric phosphate dihydrate is removed, so that the nano flaky ferric phosphate is obtained.
In the invention, ferrous oxide containing ferrous iron and an oxidant are sequentially added into a phosphoric acid solution to carry out redox reaction to obtain white superfine ferric phosphate dihydrate slurry, and then the white superfine ferric phosphate dihydrate slurry is washed, filtered, dried and dehydrated at high temperature to obtain light yellow ferric phosphate powder. According to the invention, ferrous ions are oxidized by adopting a solid-liquid phase synthesis idea, so that phase transformation and structural reconstruction of iron source components are realized, and synthesis of the nano flaky iron phosphate which is uniform, has obvious crystal face oriented growth characteristics and has good sintering activity and flaky thickness of about 50nm is facilitated.
The invention also provides LiFePO4the/C positive electrode active material is prepared from the nano flaky iron phosphate and specifically comprises the following components:
1) mixing and wet-milling nano flaky iron phosphate, a lithium source and an organic carbon source, mixing lithium and coating carbon, and drying to obtain a precursor;
2) sintering the precursor obtained in the step 1) under a protective atmosphere to obtain LiFePO4a/C positive electrode active material.
According to the invention, nano flaky iron phosphate is mixed with a carbon source and a lithium source by ball milling, the particle size of slurry particles is further reduced by means of high-energy mechanical force, agglomerated particles in the slurry are uniformly dispersed, uniform precursor slurry is prepared, and after drying, the precursor is sintered at high temperature, so that the crystallization property of the material is improved, the crystal phase purity is improved, the grain size is reduced, meanwhile, the construction of a conductive carbon network layer on the particle surface is realized, and the LiFePO is effectively improved4The intrinsic defects of the material such as low lithium ion diffusion rate and poor electronic conductivity are overcome, and the LiFePO with stable structure and excellent electrochemical performance and with the primary particle size of about 0.2-1 mu m is finally prepared4And C, material.
Preferably, in step 1), the molar ratio of iron in the nano flaky iron phosphate to lithium in the lithium source is 1: 1-1.03; the lithium source is lithium carbonate; the organic carbon source is at least one of polyethylene glycol, starch, cyclodextrin, glucose and sucrose, and the organic carbon source is LiFePO4The carbon content of the/C anode material is 1.0-2.0wt percent.
Preferably, in the step 1), the wet grinding medium is alcohol, the rotating speed is 400-.
Preferably, in step 2), the protective atmosphere is nitrogen, argon, an argon-hydrogen mixed gas or a nitrogen-hydrogen mixed gas atmosphere.
Preferably, in the step 2), the sintering temperature is 600-750 ℃; the sintering time is 4-15 h.
The sheet thickness of the iron phosphate material prepared by the method is about 50nm, and the diffusion distance of lithium ions in solid phase synthesis is shortened by the smaller primary particle size, so that the material has good electrochemical performance. Further, it was found that LiFePO4The grain diameter of the primary particles of the/C material is about 0.2-1 mu m, and the material has better electrochemical performance.
The invention also provides a lithium ion battery anode material which comprises the LiFePO4a/C positive electrode active material.
The invention has the advantages that:
1. the invention adopts ferroferric oxide with wide sources or ferrous oxide in steelmaking converter ash as an iron source, prepares the nano flaky iron phosphate by a solid-liquid phase conversion method, and has simple reaction conditions and convenient operation. The efficient utilization of mineral raw materials or smelting waste is realized, and the sheet iron phosphate is prepared, so that the prepared final product lithium iron phosphate has good electrochemical performance.
2. The technical scheme of the invention has simple synthesis process, the phosphoric acid mother liquor obtained after washing and filtering the ferric phosphate dihydrate slurry can be recycled, no wastewater is generated in the whole synthesis process, and green production is realized.
3. According to the invention, ferrous ions are oxidized by adopting a solid-liquid phase synthesis idea, so that phase transformation and structural reconstruction of iron source components are realized, and the synthesis of the nano flaky iron phosphate which is uniform, has obvious crystal face oriented growth characteristics and has good sintering activity is facilitated. Researches show that the sheet thickness of the synthesized ferric phosphate material is about 50nm, the diffusion distance of lithium ions in solid phase synthesis is shortened by the smaller primary particle size, and Li+The ion migration rate is beneficial to the lattice recombination and LiFePO in the synthesis process4The lithium iron phosphate material is ensured to have electrochemical performance and is beneficial to processing performance。
Drawings
FIG. 1 is an XRD pattern of iron phosphate dihydrate and iron phosphate prepared in example 1 of the present invention;
fig. 2 is an SEM image of iron phosphate prepared in example 1 of the present invention;
fig. 3 is a performance graph of lithium iron phosphate prepared in example 1 of the present invention for 100 cycles;
fig. 4 is an SEM image of iron phosphate prepared in example 2 of the present invention;
fig. 5 is an SEM image of lithium iron phosphate prepared in example 2 of the present invention;
fig. 6 is a 200-cycle performance graph of lithium iron phosphate prepared in example 2 of the present invention;
fig. 7 is an SEM image of iron phosphate prepared in example 3 of the present invention;
fig. 8 is an SEM image of lithium iron phosphate prepared in example 3 of the present invention;
fig. 9 is a 200-cycle performance graph of lithium iron phosphate prepared in example 3 of the present invention;
figure 10 is an SEM image of iron phosphate prepared according to example 4 of the present invention;
fig. 11 is a graph of performance of lithium iron phosphate prepared in example 4 of the present invention for 100 cycles;
fig. 12 is an SEM image of lithium iron phosphate prepared in example 5 of the present invention;
fig. 13 is a graph of cycle 80-cycle performance of lithium iron phosphate prepared in comparative example 1 of the present invention;
fig. 14 is a graph of cycle 80-cycle performance of lithium iron phosphate prepared in comparative example 2 of the present invention;
fig. 15 is a graph of performance for 100 cycles of lithium iron phosphate prepared according to comparative example 3 of the present invention;
fig. 16 is an SEM image of lithium iron phosphate prepared in comparative example 4 of the present invention;
fig. 17 is a graph of rate performance at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C rates for lithium iron phosphate prepared in comparative example 4 of the present invention.
Detailed Description
The present invention will be further described with reference to the following examples and the accompanying drawings.
The testing process of the anode material comprises the following steps: the material is made into a CR2025 button cell for charge and discharge cycle test. Preparing an electrode by adopting a coating method, taking N-methyl-2-pyrrolidone (NMP) as a solvent, respectively weighing an active substance, acetylene black and PVDF according to a mass ratio of 8:1:1, uniformly mixing, coating on a pretreated aluminum foil, and drying in a vacuum drying oven at 120 ℃ to obtain a positive plate. In a glove box filled with argon, a button cell is assembled by taking a metal lithium sheet as a negative electrode, 1 mol.L-1 LiPF6 dissolved in Ethylene Carbonate (EC), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC) (the volume ratio is 1:1:1) as an electrolyte and a Celgard2400 porous polypropylene membrane as a diaphragm, and electrochemical tests are carried out on a Land electrochemical instrument.
Example 1
Weighing 0.24mol of 85% phosphoric acid with concentration into a beaker, adding 240ml of deionized water to dilute the phosphoric acid, wherein the molar weight of the phosphoric acid is excessive by 2 times (relative to an iron source), weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted phosphoric acid, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and slowly adding 0.03mol of 30% hydrogen peroxide after 5-30min, wherein the hydrogen peroxide is 1.5 times of the theoretical amount. Stirring in water bath, reacting to obtain white slurry, vacuum filtering, washing with water, air drying to obtain ferric phosphate dihydrate, calcining at 550 deg.C in muffle furnace for 4 hr to obtain sheet ferric phosphate, and analyzing the two by X-ray powder diffraction, as shown in FIG. 1, the phase is FePO4·2H2O (a) and FePO4(b) In that respect Scanning the calcined product of this embodiment by using a scanning electron microscope, as shown in fig. 2, the morphology of the calcined product is a laminated sheet with uniform distribution, the thickness of the sheet is about 50nm, and the diffusion distance of lithium ions during solid phase synthesis is shortened by the smaller primary particle size. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then placing the yellow product in an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. The anode material has better electrochemical performance through detection, as shown in figure 3, when constant-current charge and discharge test is carried out at constant temperature and under the multiplying power of 1C between 2.5V and 4.1V, the specific discharge capacity of a product is 145.2mAh g-1。
Example 2
Weighing 0.24mol of 85% phosphoric acid with concentration into a beaker, adding 240ml of deionized water to dilute the phosphoric acid, wherein the molar weight of the phosphoric acid is excessive by 2 times (relative to an iron source), weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted phosphoric acid, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and after 5-30min, slowly adding 0.04mol of 30% hydrogen peroxide, wherein the hydrogen peroxide accounts for 2 times of the theoretical amount. Stirring in a water bath, fully reacting, converting into white slurry, performing suction filtration, washing, and air drying to obtain ferric phosphate dihydrate, and roasting in a muffle furnace at 550 ℃ for 4 hours to obtain the flaky ferric phosphate.
The calcined product of this example was scanned by a scanning electron microscope, and as shown in fig. 4, the morphology of the calcined product was also a laminated sheet with uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then placing the yellow product in an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. LiFePO obtained in this example was scanned by a scanning electron microscope4the/C product, as shown in FIG. 5, has a relatively uniform morphology of approximately 0.5 μm flaky spheroidal particles and a relatively uniform distribution. Under constant temperature, the specific discharge capacity of the product 1C after 200 times of circulation is 150.1mAh g-1As shown in fig. 6, the capacity retention rate was 93.6%, and the synthesized product had excellent cycle properties.
Example 3
Weighing 0.3mol of 85% phosphoric acid with concentration into a beaker, adding 300ml of deionized water to dilute the phosphoric acid, wherein the molar excess of the phosphoric acid is 2.5 times (relative to an iron source), weighing 0.04mol of ferroferric oxide, slowly adding the weighed ferroferric oxide into the diluted phosphoric acid, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and slowly adding 0.04mol of 30% hydrogen peroxide after 5-30min, wherein the hydrogen peroxide is 2 times of the theoretical amount. Stirring in a water bath, fully reacting, converting into white slurry, performing suction filtration, washing, and air drying to obtain ferric phosphate dihydrate, and roasting in a muffle furnace at 550 ℃ for 4 hours to obtain the flaky ferric phosphate. The product of this example was scanned using a scanning electron microscope, as shown in FIG. 7The appearance of the material is a laminated sheet shape with uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then placing the yellow product in an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. LiFePO continuously prepared by the embodiment through scanning by using a scanning electron microscope4The morphology of the/C product is spherical-like particles with a relatively uniform distribution of about 0.3 μm, as shown in FIG. 8. Under constant temperature, the specific discharge capacity of the product 1C after 200 times of circulation is 152.7mAh g-1As shown in fig. 9, the capacity retention rate is 95.79%, the capacity is not attenuated basically, and the synthesized product has excellent cycle performance.
Example 4
Weighing 0.36mol of 85% phosphoric acid with concentration in a beaker, adding 360ml of deionized water to dilute the phosphoric acid, wherein the molar amount of the phosphoric acid is excessive by 3 times (relative to an iron source), weighing 0.12mol of ferrous oxide and slowly adding the ferrous oxide into the diluted phosphoric acid, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and after 5-30min, slowly adding 0.12mol of 30% hydrogen peroxide, wherein the hydrogen peroxide accounts for 2 times of the theoretical amount. Stirring in a water bath, fully reacting, converting into white slurry, performing suction filtration, washing, and air drying to obtain ferric phosphate dihydrate, and roasting in a muffle furnace at 550 ℃ for 4 hours to obtain the flaky ferric phosphate. The product of this example was scanned by a scanning electron microscope, and as shown in fig. 10, the appearance was similar to that described above, and the product was a laminated sheet with a uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then placing the yellow product in an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. Under constant temperature, the specific discharge capacity of the product 1C after 100 times of circulation is 124.1mAh g-1As shown in fig. 11.
Example 5
Considering that the ferric phosphate precipitation mother liquor can be continuously recycled as a phosphorus-containing solution, weighing and slowly adding 0.04mol of ferroferric oxide into the residual phosphoric acid in the example 2, continuously weighing and adding 200ml of deionized water, heating and stirring in water bath at 80 ℃, slowly adding 0.04mol of hydrogen peroxide and 30% of hydrogen peroxide after 5-30min, stirring in water bath for full reaction to obtain white slurry, performing suction filtration, water washing and blast drying to obtain ferric phosphate dihydrate, and roasting in a muffle furnace at 600 ℃ for 4h to obtain the ferric phosphate. The product of this example was scanned by a scanning electron microscope, and as shown in fig. 12, the morphology thereof was also a laminated sheet with a uniform distribution.
Comparative example 1
Compared with the example 1, the difference is that no hydrogen peroxide is added in the heating process.
Weighing 0.24mol of 85% phosphoric acid with concentration into a beaker, adding 240ml of deionized water to dilute the phosphoric acid, wherein the molar weight of the phosphoric acid is excessive by 2 times (relative to an iron source), weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted phosphoric acid, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and after stirring and reacting in the water bath, the solution is black and is not converted into white slurry. And (4) carrying out suction filtration, air drying and roasting at 550 ℃ in a muffle furnace for 4 hours to obtain an iron phosphate mixture. 10g of the above product were taken, 0.03315mol of Li2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then putting the product into an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. At constant temperature, the specific discharge capacity of the product at 1C is only 73.5mAh g-1The performance was not good as shown in fig. 13.
Comparative example 2
The only difference compared to example 2 is that the phosphorus source used is monoammonium phosphate.
Weighing 0.24mol of monoammonium phosphate into a beaker, adding 240ml of deionized water to dissolve and dilute the monoammonium phosphate, wherein the molar excess of the monoammonium phosphate is 3 times (relative to an iron source), weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted monoammonium phosphate, stirring and heating the mixture in a water bath at the temperature of 80 ℃, and slowly adding 0.04mol of 30% hydrogen peroxide after 5-30min, wherein the hydrogen peroxide is 2 times of the theoretical amount. And after the mixture is stirred in a water bath and fully reacts, the solution is gray black, and is subjected to suction filtration, water washing and forced air drying, and then is roasted for 4 hours at 550 ℃ in a muffle furnace to obtain an iron phosphate mixture. Taking 10g of the aboveProduct, 0.03315mol Li2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then putting the product into an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. At constant temperature, the specific discharge capacity of the product at 1C is 93.7mAh g-1As shown in fig. 14.
Comparative example 3
Compared with example 4, the difference is only that the iron source used is different, namely iron oxide Fe2O3。
0.36mol of 85% phosphoric acid with a concentration of 0.36mol is weighed into a beaker and 360ml of deionized water is added to dilute the phosphoric acid, the molar excess of the phosphoric acid is 3 times (relative to the iron source), 0.06mol of iron oxide is weighed and slowly added into the diluted phosphoric acid, the mixture is stirred and heated in a water bath at the temperature of 80 ℃, and after 5-30min, 0.24mol of 30% hydrogen peroxide is slowly added, wherein the hydrogen peroxide accounts for 2 times of the theoretical amount. After the reaction was stirred in a water bath, the color remained reddish brown. And carrying out suction filtration and forced air drying, and then roasting in a muffle furnace at 550 ℃ for 4h to obtain an iron phosphate mixture. 10g of the above product were taken, 0.03315mol of Li2CO3Ball milling 0.22g of PEG and 1g of cyclodextrin (the medium is alcohol, and the rotating speed is 400r/min) for 4h, and then blowing and drying. Then putting the product into an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO4and/C. At constant temperature, the specific discharge capacity of the product at 1C is 90mAh g-1Left and right, and poor cycle performance, as shown in fig. 15.
Comparative example 4
Compared with example 2, the difference is that phosphoric acid is not excessive, and LiFePO is prepared by direct sintering by using solid phase ball milling according to stoichiometric ratio4/C。
Weighing 0.12mol of 85% phosphoric acid with concentration in a ball milling tank, adding 120ml of deionized water heated to 80 ℃ to dilute the phosphoric acid, wherein the phosphoric acid is not excessive, weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted phosphoric acid, performing ball milling dispersion for 1h, slowly adding 0.04mol of 30% hydrogen peroxide, wherein the hydrogen peroxide is 2 times of the theoretical amount, continuing ball milling for 3h, and performing air blast drying on the obtained slurry. Then 0.06mol of Li is weighed2CO3，0.4gPEGAdding 2g of starch into a ball milling tank, dispersing with 50ml of ethanol, continuing ball milling for 4h to obtain lithium iron phosphate precursor slurry, then placing the black slurry into an atmosphere furnace, calcining at 650 ℃ for 6h under the protection of argon to obtain LiFePO4and/C. The product of this example was scanned by a scanning electron microscope, and as shown in FIG. 16, the primary particles had a non-uniform particle size distribution and a significant interparticle agglomeration. At constant temperature, the specific discharge capacity of the product at 1C is 130.3mAh g-1However, the rate capability is not good, as shown in FIG. 17, the first discharge specific capacity of the material at 0.1C, 1C, 5C is 146.8mAh g-1、130.3mAh g-1、14.2mAh g-1。
Claims (10)
1. A preparation method of nano flaky iron phosphate is characterized by comprising the following steps:
1) adding ferrous oxide containing ferrous iron into a phosphoric acid solution, then adding an oxidant, and carrying out heat preservation reaction to obtain dihydrate ferric phosphate slurry;
2) washing, filtering, drying and roasting the dihydrate ferric phosphate slurry to obtain the nano flaky ferric phosphate.
2. The method for preparing nano flaky iron phosphate according to claim 1, characterized in that: in the step 1), the concentration of the phosphoric acid solution is 1-2 mol/L.
3. The method for preparing nano flaky iron phosphate according to claim 1, characterized in that: in the step 1), the iron oxide is at least one of ferroferric oxide and ferrous oxide, the ferroferric oxide is magnetite beneficiated powder or chemically pure powder, the purity of the ferroferric oxide is more than 99%, and the purity of the ferrous oxide is more than 99%; the molar ratio of phosphorus in the phosphoric acid solution to iron in the iron oxide is 2-3: 1.
4. The method for preparing nano flaky iron phosphate according to claim 1, characterized in that: in step 1), the oxidant is 30 wt% of H2O2In an amount theoretically capable of oxidizing ferrous iron in the iron oxide1-2 times.
5. The method for preparing nano flaky iron phosphate according to claim 1, characterized in that: in the step 1), the pH value of the heat preservation reaction is 1-2, the temperature is 60-90 ℃, and the time is 0.5-5 h.
6. The method for preparing nano flaky iron phosphate according to claim 1, characterized in that: in the step 2), the roasting temperature is 500-600 ℃, and the time is 2-6 h.
7. LiFePO4the/C positive electrode active material is prepared from the nano flaky iron phosphate of any one of claims 1 to 6, and specifically comprises the following components:
1) mixing and wet-milling nano flaky iron phosphate, a lithium source and an organic carbon source, mixing lithium and coating carbon, and drying to obtain a precursor;
2) sintering the precursor obtained in the step 1) under a protective atmosphere to obtain LiFePO4a/C positive electrode active material.
8. The LiFePO according to claim 14a/C positive electrode active material characterized in that: in the step 1), the molar ratio of iron in the nano flaky iron phosphate to lithium in the lithium source is 1: 1-1.03; the lithium source is lithium carbonate; the organic carbon source is at least one of polyethylene glycol, starch, cyclodextrin, glucose and sucrose, and the organic carbon source is LiFePO4The carbon content of the/C anode material is 1.0-2.0wt percent.
9. The LiFePO according to claim 14a/C positive electrode active material characterized in that: in the step 2), the protective atmosphere is nitrogen, argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas atmosphere; the sintering temperature is 600-750 ℃; the sintering time is 4-15 h.
10. A lithium ion battery positive electrode material comprising the LiFePO according to any one of claims 7 to 94a/C positive electrode active material.
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