CN113651303B - Preparation method of nano flaky ferric phosphate and LiFePO prepared by using same 4 C positive electrode active material - Google Patents
Preparation method of nano flaky ferric phosphate and LiFePO prepared by using same 4 C positive electrode active material Download PDFInfo
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Abstract
The invention discloses a preparation method of nano flaky ferric phosphate and LiFePO prepared by using the same 4 a/C positive electrode active material comprising the steps of: 1) Adding ferrous iron oxide into phosphoric acid solution, then adding oxidant, and reacting at a constant temperature to obtain ferric phosphate dihydrate slurry; 2) Washing, filtering, drying and roasting the dihydrate ferric phosphate slurry to obtain nano flaky ferric phosphate; 3) Mixing and wet-milling nano flaky ferric phosphate, a lithium source and an organic carbon source, mixing lithium and coating carbon, and drying to obtain a precursor; 4) Sintering the precursor in protective atmosphere to obtain LiFePO 4 and/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 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 ferric phosphate and LiFePO prepared by using the same 4 and/C positive electrode active material.
Background
With irreversible consumption of fossil energy, new energy is becoming an indispensable part of people's life, with lithium ion batteries being most commonly used. The lithium iron phosphate anode material has good electrochemical performance, stable charge and discharge platform, no toxicity, no pollution, long cycle life and good safety performance, and can be used in a high-temperature environment. Accordingly, the lithium iron phosphate cathode materials have been widely studied by those skilled in the art. The lithium iron phosphate positive electrode material has the defects of larger tap density fluctuation, lower compaction density, poor electronic conductivity, low lithium ion diffusion rate and the like, and the morphology feature and electrochemical performance of the lithium iron phosphate material are determined to a great extent by taking the ferric phosphate as a precursor mainly used for synthesizing the lithium iron phosphate of the positive electrode material. Therefore, improvement of various properties of lithium iron phosphate by controlling iron phosphate has also become a trend in this field.
At present, the preparation process of the iron phosphate generally takes soluble ferrous sulfate as a raw material, and iron phosphate precursors with certain agglomerates are obtained through a coprecipitation process, wherein metal salts containing anions (sulfate radical, nitrate radical 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 wastewater is required to be treated, and the process cost is increased. Therefore, there is a need to develop a synthetic technique with high atomic 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 ferric phosphate and LiFePO prepared by using the same 4 Preparation method of/C positive electrode active material by solid-liquid phase conversionPreparing nano flaky ferric phosphate, and improving the morphological distribution of the product lithium iron phosphate through the flaky ferric phosphate, thereby improving the electrochemical performance and physical performance of the final lithium iron phosphate.
A method for preparing nano flaky ferric phosphate, which comprises the following steps:
1) Adding ferrous iron oxide into phosphoric acid solution, then adding oxidant, and reacting at a constant temperature to obtain ferric phosphate dihydrate slurry;
2) Washing, filtering, drying and roasting the dihydrate ferric phosphate slurry to obtain the nano flaky ferric phosphate.
Preferably, in step 1), the concentration of the phosphoric acid solution is 1-2mol/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 chemical 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.
Preferably, in step 1), the oxidant is 30wt% H 2 O 2 The addition amount is 1-2 times of the theoretical amount of ferrous iron in the iron oxide.
Preferably, in the step 1), the pH value of the heat preservation reaction is 1-2, the temperature is 60-90 ℃ and the time is 0.5-5h. In the invention, the whole process of preparing the ferric phosphate dihydrate is carried out under heating, and the ferric phosphate fully reacts under the stirring action to form uniform white thick ferric phosphate slurry.
Preferably, in step 2), the calcination temperature is 500-600℃and the time is 2-6 hours. In the invention, the dihydrate ferric phosphate is sintered at high temperature, and crystal water in the dihydrate ferric phosphate is removed, so that the nano flaky ferric phosphate is obtained.
In the invention, ferrous iron oxide and oxidant are added into phosphoric acid solution in turn to generate oxidation-reduction reaction, so as to obtain white superfine ferric phosphate dihydrate slurry, and then the white superfine ferric phosphate slurry is washed, filtered, dried and dehydrated at high temperature to obtain light yellow ferric phosphate powder. The invention adopts the solid-liquid phase synthesis thought to oxidize ferrous ions, realizes the phase transformation and the structural reconstruction of iron source components, and is favorable for synthesizing the nano flaky ferric phosphate which is uniform and consistent, has obvious crystal face orientation growth characteristics and good sintering activity and has the flaky thickness of about 50 nm.
The invention also provides LiFePO 4 The positive electrode active material is prepared from the nano flaky ferric phosphate, and specifically comprises the following components:
1) Mixing and wet-milling nano flaky ferric 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) in a protective atmosphere to obtain LiFePO 4 and/C positive electrode active material.
According to the invention, the nano flaky ferric phosphate is mixed with a carbon source and a lithium source by utilizing 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, a uniform precursor slurry is prepared, after the precursor slurry is dried, the precursor is sintered at high temperature, the crystallization performance of the material is perfected, the crystal phase purity is improved, the grain size is reduced, meanwhile, the construction of a conductive carbon network layer is realized on the particle surface, and LiFePO is effectively improved 4 The material has the inherent defects of low lithium ion diffusion rate and poor electronic conductivity, and finally prepares LiFePO with stable structure and excellent electrochemical performance, wherein the primary particle diameter is about 0.2-1 mu m 4 and/C material.
Preferably, in step 1), the molar ratio of iron in the nano-sheet 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 is LiFePO 4 The carbon content of the positive electrode material/C is 1.0-2.0 wt%.
Preferably, in the step 1), the wet grinding medium is alcohol, the rotating speed is 400-600r/min, and the time is 2-4h.
Preferably, in the step 2), the protective atmosphere is nitrogen, argon-hydrogen mixed gas or nitrogen-hydrogen mixed gas atmosphere.
Preferably, in step 2), the sintering temperature is 600 ℃ to 750 ℃; the sintering time is 4-15h.
The sheet thickness of the iron phosphate material prepared by the invention is about 50nm, and the smaller primary particle size shortens the diffusion distance of lithium ions in the solid phase synthesis process, so that the material has good electrochemical performance. Further, it was found that LiFePO 4 The primary particle size of the material/C 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 LiFePO 4 and/C positive electrode active material.
The invention has the advantages that:
1. the invention adopts widely available ferroferric oxide or ferrous oxide in steelmaking converter ash as an iron source, prepares nano flaky ferric phosphate by a solid-liquid phase conversion method, and has simple reaction conditions and convenient operation. The method realizes the high-efficiency utilization of mineral raw materials or smelting waste materials, prepares the flaky ferric phosphate, and ensures that the prepared final product lithium iron phosphate has good electrochemical performance.
2. According to the technical scheme, the synthesis process is simple, the phosphate mother liquor after washing and filtering of the ferric phosphate dihydrate slurry can be recycled, no waste water is generated in the whole synthesis process, and green production is realized.
3. The invention adopts the solid-liquid phase synthesis thought to oxidize ferrous ions, realizes the phase transformation and structure reconstruction of iron source components, and is favorable for synthesizing the nano flaky ferric phosphate which is uniform and consistent, has obvious crystal face orientation growth characteristics and good sintering activity. The research shows that the sheet thickness of the synthesized ferric phosphate material is about 50nm, the smaller primary particle diameter shortens the diffusion distance of lithium ions in the solid phase synthesis, and Li + The ion migration rate is favorable for lattice recombination and LiFePO in the synthesis process 4 The formation of the lithium iron phosphate material ensures the electrochemical performance of the lithium iron phosphate material and is beneficial to the processing performance.
Drawings
FIG. 1 is an XRD pattern of iron phosphate dihydrate prepared in example 1 of the invention, and of iron phosphate;
FIG. 2 is an SEM image of the iron phosphate prepared according to example 1 of the present invention;
FIG. 3 is a graph showing the cycle 100 performance of lithium iron phosphate prepared in example 1 of the present invention;
FIG. 4 is an SEM image of the iron phosphate prepared according to example 2 of the present invention;
FIG. 5 is an SEM image of lithium iron phosphate prepared according to example 2 of the invention;
FIG. 6 is a graph of the cycle 200 performance of lithium iron phosphate prepared in example 2 of the present invention;
FIG. 7 is an SEM image of the iron phosphate prepared according to example 3 of the present invention;
FIG. 8 is an SEM image of lithium iron phosphate prepared according to example 3 of the invention;
FIG. 9 is a graph of the cycle 200 performance of lithium iron phosphate prepared in example 3 of the present invention;
FIG. 10 is an SEM image of the iron phosphate of example 4 of the present invention;
FIG. 11 is a graph of the cycle 100 performance of lithium iron phosphate prepared in example 4 of the present invention;
FIG. 12 is an SEM image of lithium iron phosphate prepared according to example 5 of the invention;
FIG. 13 is a graph showing the cycle 80 performance of the lithium iron phosphate prepared in comparative example 1 of the present invention;
FIG. 14 is a graph showing the cycle 80 of the lithium iron phosphate prepared in comparative example 2 of the present invention;
FIG. 15 is a graph showing the cycle 100 of the lithium iron phosphate prepared in comparative example 3 according to the present invention;
FIG. 16 is an SEM image of lithium iron phosphate of comparative example 4 of the present invention;
fig. 17 is a graph showing the rate performance of lithium iron phosphate prepared in comparative example 4 of the present invention at 0.1C, 0.2C, 0.5C, 1C, 2C, 5C rates.
Detailed Description
The invention is further described below with reference to examples and figures.
The testing process of the positive electrode material comprises the following steps: the material was fabricated into a CR2025 button cell for charge and discharge cycle testing. The electrode is prepared by adopting a film coating method, N-methyl-2-pyrrolidone (NMP) is taken as a solvent, active substances, acetylene black and PVDF are respectively weighed according to the mass ratio of 8:1:1, uniformly mixed, coated on the pretreated aluminum foil, and placed in a vacuum drying oven to be dried at 120 ℃ to obtain the positive plate. In a glove box filled with argon, a button cell is assembled by taking a metal lithium sheet as a negative electrode, dissolving 1 mol.L-1 LiPF6 in Ethylene Carbonate (EC) +dimethyl carbonate (DMC) +ethyl methyl carbonate (EMC) (the volume ratio is 1:1:1) as an electrolyte, taking a Celgard2400 porous polypropylene film as a diaphragm, and performing electrochemical test on a Land electrochemical instrument.
Example 1
0.24mol of 85% phosphoric acid is weighed into a beaker and 240ml of deionized water is added to dilute the phosphoric acid, the molar quantity of the phosphoric acid is 2 times (relative to the iron source), 0.04mol of ferroferric oxide is weighed and slowly added into the diluted phosphoric acid, the diluted phosphoric acid is stirred and heated in a water bath at the temperature of 80 ℃ for 5-30min, and then 0.03mol of 30% hydrogen peroxide is slowly added, wherein the hydrogen peroxide is 1.5 times of the theoretical quantity. After fully reacting in water bath, converting into white slurry, carrying out suction filtration, washing with water, air drying to obtain ferric phosphate dihydrate, roasting in a muffle furnace at 550 ℃ for 4 hours to obtain flaky ferric phosphate, and analyzing the two by using X-ray powder diffraction, wherein the phase is FePO as shown in figure 1 4 ·2H 2 O (a) and FePO 4 (b) A. The invention relates to a method for producing a fibre-reinforced plastic composite The calcined product of this example was scanned by a scanning electron microscope, and as shown in fig. 2, the morphology of the calcined product was in the form of laminated sheets with relatively uniform distribution, the thickness of the sheets was about 50nm, and the smaller primary particle size shortened the diffusion distance of lithium ions during solid phase synthesis. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the yellow product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. As shown in figure 3, the positive electrode material has better electrochemical performance, and when constant-current charge-discharge test is carried out between 2.5 and 4.1V at a constant temperature and 1C multiplying power, the specific discharge capacity of the product is 145.2mAh g -1 。
Example 2
0.24mol of 85% phosphoric acid is weighed into a beaker and 240ml of deionized water is added to dilute the phosphoric acid, the molar quantity of the phosphoric acid is 2 times (relative to the iron source), 0.04mol of ferroferric oxide is weighed and slowly added into the diluted phosphoric acid, the diluted phosphoric acid is stirred and heated in a water bath at the temperature of 80 ℃ for 5-30min, and then 0.04mol of 30% hydrogen peroxide is slowly added, wherein the molar quantity of the hydrogen peroxide is 2 times of the theoretical quantity. The mixture is stirred in water bath to fully react and then is converted into white slurry, the white slurry is subjected to suction filtration, water washing and forced air drying to obtain ferric phosphate dihydrate, and then the ferric phosphate dihydrate is roasted in a muffle furnace for 4 hours at 550 ℃ 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 was also in the form of laminated sheets with a relatively uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the yellow product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. LiFePO obtained in this example was scanned using a scanning electron microscope 4 As shown in FIG. 5, the morphology of the product of the method is more uniform and the product of the method is more uniformly distributed and is approximately 0.5 mu m of flaky spheroidal particles. At constant temperature, the specific discharge capacity of the product 1C for 200 times is 150.1mAh g -1 As shown in fig. 6, the capacity retention rate was 93.6%, and the synthesized product had excellent cycle performance.
Example 3
0.3mol of 85% phosphoric acid is weighed into a beaker and 300ml of deionized water is added to dilute the phosphoric acid, the molar quantity of the phosphoric acid is 2.5 times (relative to the iron source), 0.04mol of ferroferric oxide is weighed and slowly added into the diluted phosphoric acid, the diluted phosphoric acid is stirred and heated in a water bath at the temperature of 80 ℃ for 5-30min, and then 0.04mol of 30% hydrogen peroxide is slowly added, wherein the molar quantity of the hydrogen peroxide is 2 times the theoretical quantity. The mixture is stirred in water bath to fully react and then is converted into white slurry, the white slurry is subjected to suction filtration, water washing and forced air drying to obtain ferric phosphate dihydrate, and then the ferric phosphate dihydrate is roasted in a muffle furnace for 4 hours at 550 ℃ to obtain the flaky ferric phosphate. The product of this example was scanned using a scanning electron microscope, as shown in FIG. 7, and the morphology was in the form of a laminated sheet with a relatively uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then the yellow product is placed in an atmosphere furnace and is protected by argon at 650 DEG CCalcining for 6h to obtain LiFePO 4 and/C. The LiFePO prepared in this example was scanned by a scanning electron microscope 4 As shown in FIG. 8, the morphology of the product is similar spherical particles with a relatively uniform distribution of about 0.3 μm, and the distribution is relatively uniform. At constant temperature, the specific discharge capacity of the product 1C is 152.7mAh g after 200 times of circulation -1 As shown in fig. 9, the capacity retention rate was 95.79%, the capacity was not substantially attenuated, and the synthesized product had excellent cycle performance.
Example 4
0.36mol of 85% phosphoric acid was weighed into a beaker and 360ml of deionized water was added to dilute the phosphoric acid, the molar excess of which was 3 times (relative to the iron source), 0.12mol of ferrous oxide was weighed and slowly added to the diluted phosphoric acid, heated in a water bath with stirring at 80℃for 5-30min, and after 5-30min 0.12mol of 30% hydrogen peroxide was slowly added, which was 2 times the theoretical amount. The mixture is stirred in water bath to fully react and then is converted into white slurry, the white slurry is subjected to suction filtration, water washing and forced air drying to obtain ferric phosphate dihydrate, and then the ferric phosphate dihydrate is roasted in a muffle furnace for 4 hours at 550 ℃ to obtain the flaky ferric phosphate. The product of this example was scanned by a scanning electron microscope, as shown in FIG. 10, and had a morphology similar to that described above, and was in the form of a laminated sheet with a relatively uniform distribution. 0.0663mol of ferric phosphate and 0.03315mol of Li are taken 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the yellow product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. At constant temperature, the specific discharge capacity of the product 1C for 100 times is 124.1mAh g -1 As shown in fig. 11.
Example 5
Considering that ferric phosphate precipitation mother liquor can be reused as phosphorus-containing solution, weighing 0.04mol of ferroferric oxide and slowly adding the ferroferric oxide into the rest phosphoric acid in the example 2, continuously weighing 200ml of deionized water, adding the deionized water into the solution, heating and stirring the solution in a water bath at 80 ℃ for 5-30min, slowly adding 0.04mol of 30% hydrogen peroxide, stirring the solution in the water bath for full reaction, converting the solution into white slurry, filtering the white slurry, washing the white slurry with water, and air-drying the white slurry to obtain ferric phosphate dihydrate, and roasting the ferric phosphate 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, as shown in FIG. 12, and the morphology was also in the form of a laminated sheet with a relatively uniform distribution.
Comparative example 1
The difference compared with example 1 is that hydrogen peroxide is not added during the heating process.
0.24mol of 85% phosphoric acid was weighed into a beaker and 240ml of deionized water was added to dilute the phosphoric acid, the molar excess of the phosphoric acid was 2 times (relative to the iron source), 0.04mol of ferroferric oxide was weighed and slowly added to the diluted phosphoric acid, and the solution was stirred and heated in a water bath at 80 ℃ and after the water bath stirring reaction, the solution appeared black without conversion to white slurry. And (3) carrying out suction filtration, forced air drying and roasting for 4 hours at 550 ℃ in a muffle furnace to obtain the iron phosphate mixture. 10g of the above product was taken, 0.03315mol of Li 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. At constant temperature, the specific discharge capacity of the product at 1C is only 73.5mAh g -1 The performance was poor as shown in fig. 13.
Comparative example 2
The only difference compared to example 2 is that the phosphorus source used is monoammonium phosphate.
0.24mol of monoammonium phosphate is weighed into a beaker and 240ml of deionized water is added to dissolve and dilute monoammonium phosphate, the molar quantity of monoammonium phosphate is 3 times (relative to the iron source), 0.04mol of ferroferric oxide is weighed and slowly added into diluted monoammonium phosphate, the diluted monoammonium phosphate is heated in a water bath under stirring at the temperature of 80 ℃ for 5-30min, and 0.04mol of 30% hydrogen peroxide is slowly added, wherein the hydrogen peroxide is 2 times of the theoretical quantity. After the water bath is stirred and fully reacted, the solution is gray black, and is subjected to suction filtration, water washing and forced air drying, and then baked for 4 hours at 550 ℃ in a muffle furnace, so as to obtain the iron phosphate mixture. 10g of the above product was taken, 0.03315mol of Li 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. At constant temperature, the specific volume of the product discharged at 1CThe amount was 93.7mAh g -1 As shown in fig. 14.
Comparative example 3
In comparison with example 4, the only difference is that the iron source used is iron oxide Fe 2 O 3 。
0.36mol of 85% phosphoric acid was weighed into a beaker and 360ml of deionized water was added to dilute the phosphoric acid, the molar excess of which was 3 times (relative to the iron source), 0.06mol of iron oxide was weighed and slowly added to the diluted phosphoric acid, heated in a water bath with stirring at 80℃for 5-30min, and after 5-30min 0.24mol of 30% hydrogen peroxide was slowly added, which was 2 times the theoretical amount. After stirring in water bath to react fully, the color maintains reddish brown. And (3) carrying out suction filtration and forced air drying, and roasting in a muffle furnace at 550 ℃ for 4 hours to obtain the iron phosphate mixture. 10g of the above product was taken, 0.03315mol of Li 2 CO 3 0.22g PEG and 1g cyclodextrin ball milling (medium is alcohol, rotation speed is 400 r/min) for 4h, and then blast drying. Then placing the product in an atmosphere furnace, calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. At constant temperature, the specific discharge capacity of the product at 1C is 90mAh g -1 Left and right, and the cycle performance is poor, as shown in fig. 15.
Comparative example 4
Compared with example 2, the difference is that phosphoric acid is not excessive and solid phase ball milling is used for direct sintering to prepare LiFePO according to stoichiometric ratio 4 /C。
Weighing 0.12mol of 85% phosphoric acid in a ball milling tank, adding 120ml of deionized water heated to 80 ℃ to dilute the phosphoric acid, weighing 0.04mol of ferroferric oxide, slowly adding the ferroferric oxide into the diluted phosphoric acid, ball milling and dispersing 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 carrying out forced air drying on the obtained slurry. Then weighing 0.06mol of Li 2 CO 3 Adding 0.4g PEG and 2g starch into a ball milling tank, dispersing with 50ml ethanol, continuously ball milling for 4 hours to obtain lithium iron phosphate precursor slurry, placing the black slurry into an atmosphere furnace, and calcining for 6 hours at 650 ℃ under the protection of argon to obtain LiFePO 4 and/C. Scanning the product of this example using a scanning electron microscope, e.gAs shown in FIG. 16, the primary particles were not uniformly distributed in size and the agglomeration between particles was severe. At constant temperature, the specific discharge capacity of the product at 1C is 130.3mAh g -1 However, the rate capability is not good, as shown in FIG. 17, the specific capacities of the materials at 0.1C, 1C and 5C for the first discharge are respectively 146.8mAh g -1 、130.3mAh g -1 、14.2mAh g -1 。
Claims (4)
1. The preparation method of the nano flaky ferric phosphate is characterized by comprising the following steps of:
1) Adding ferrous iron oxide into phosphoric acid solution, then adding oxidant, and reacting at a constant temperature to obtain ferric phosphate dihydrate slurry; the concentration of the phosphoric acid solution is 1-2mol/L; the mole ratio of phosphorus in the phosphoric acid solution to iron in the iron oxide is 2-3:1; the pH value of the heat preservation reaction is 1-2, the temperature is 60-90 ℃ and the time is 0.5-5h; the iron oxide is at least one of ferroferric oxide and ferrous oxide, the ferroferric oxide is magnetite beneficiated powder or chemical pure powder, the purity of the ferroferric oxide is more than 99%, and the purity of the ferrous oxide is more than 99%; the oxidant is 30wt% H 2 O 2 The addition amount is 1-2 times of the theoretical amount of ferrous iron in the iron oxide;
2) Washing, filtering, drying and roasting the dihydrate ferric phosphate slurry to obtain the nano flaky ferric phosphate.
2. The method for preparing nano sheet iron phosphate according to claim 1, wherein: in the step 2), the roasting temperature is 500-600 ℃ and the roasting time is 2-6h.
3. LiFePO 4 A positive electrode active material/C prepared from the nano sheet-shaped iron phosphate obtained by the preparation method of claim 1 or 2, specifically: 1) Mixing and wet-milling nano flaky ferric phosphate, a lithium source and an organic carbon source, mixing lithium and coating carbon, and drying to obtain a precursor; the molar ratio of iron in the nano flaky ferric phosphate to lithium in the lithium source is 1:1-1.03; the lithium source is lithium carbonate; the organic carbon source is polyethylene glycol, starch, cyclodextrin, and glucoseAt least one of sucrose, and organic carbon source is LiFePO 4 Adding the carbon content of the positive electrode material/C of 1.0-2.0 wt%; 2) Sintering the precursor obtained in the step 1) in a protective atmosphere to obtain LiFePO 4 A positive electrode active material; 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 4-15h.
4. A lithium ion battery positive electrode material comprising the LiFePO of claim 3 4 and/C positive electrode active material.
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| CN115353084A (en) * | 2022-07-06 | 2022-11-18 | 宜宾天原锂电新材有限公司 | Method for producing lithium iron phosphate by using ferric phosphate dihydrate as raw material through one-step method |
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