CN108529584B - Preparation method of high-density lithium iron phosphate cathode material - Google Patents

Preparation method of high-density lithium iron phosphate cathode material Download PDF

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CN108529584B
CN108529584B CN201810370235.8A CN201810370235A CN108529584B CN 108529584 B CN108529584 B CN 108529584B CN 201810370235 A CN201810370235 A CN 201810370235A CN 108529584 B CN108529584 B CN 108529584B
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iron phosphate
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谢香兰
杨安臣
肖水龙
熊杜娟
罗邵滨
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JIANGXI KINGLI TECHNOLOGY CO LTD
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Abstract

The invention provides a preparation method of a high-density lithium iron phosphate positive electrode material, which mainly comprises the following steps: mixing reducing iron powder and ferric orthophosphate according to a certain proportion to obtain a composite iron source; then adding deionized water into ball milling equipment, sequentially adding a lithium source, a composite iron source, a phosphorus source, a carbon source and a surfactant, and forming slurry after ball milling; the obtained slurry is injected into a diaphragm filter press for solid-liquid separation to obtain a precursor with the solid content of more than 85 percent; drying the precursor in a flash dryer to obtain a powdery precursor with the liquid content of less than 1%; and sintering the precursor powder in a kiln with protective atmosphere, cooling, and then performing jet milling to obtain the lithium iron phosphate powder. The method has the advantages of simple process, low cost and good electrochemical performance of the product.

Description

Preparation method of high-density lithium iron phosphate cathode material
Technical Field
The invention belongs to the field of green energy materials, particularly relates to the technical field of lithium batteries, and particularly relates to a preparation method of a high-density lithium iron phosphate positive electrode material.
Background
The lithium ion battery has the advantages of high specific energy, high working voltage, low self-discharge rate, long cycle life, no pollution and the like, and becomes a hotspot for power battery development. The positive electrode material, which is an important component of the lithium ion battery, is a key factor for determining the safety, capacity and price of the battery. At present, the anode material for the industrialized power lithium ion battery is mainly a lithium iron phosphate and high nickel ternary material, wherein the demand of the lithium iron phosphate material is larger.
The method is characterized in that iron phosphate, lithium carbonate and a carbon source are used as raw materials, deionized water is used as a dispersing agent, a spherical powdery precursor is obtained after centrifugal spray drying after wet ball milling and high-speed superfine grinding, the precursor is hollow spherical after centrifugal spray drying, the lithium iron phosphate material is still hollow spherical after sintering, and after air flow crushing, part of hollow spheres with larger particle size can be crushed, but the phenomenon of carbon coating on the surface of lithium iron phosphate crystal particles is stripped during crushing, and part of the hollow spheres with small particle size are still hollow spherical. Due to the existence of the hollow spherical material, the material density is low, the material is difficult to disperse in the processing process of a battery cell factory, the processing performance is poor, the phenomena of powder falling and peeling caused by rebounding of the pole piece after the pole piece is rolled to the roller are avoided, and the pole piece compaction density is low. At present, the problem of stripping hollow spheres and carbon is solved by adopting a precursor crushing mode in the industry, but after the precursor is crushed, materials are fine and bulky, the sintering capacity can be greatly reduced, and the mass and heat transfer effect in the sintering process is further influenced due to the fact that the materials are fine and the specific surface and the gaps are large.
The drying link in the preparation process of lithium iron phosphate is yet to be explored continuously, and particularly in the process of preparing lithium iron phosphate by wet mixing, the drying process is more important. Insufficient drying can cause the material to be uneven, and the material can be coagulated in the sintering process, so that the performance of the lithium iron phosphate positive electrode material is influenced. In addition, the drying efficiency is low, which indirectly results in high production cost.
Disclosure of Invention
The invention aims to provide a method for preparing a high-density lithium iron phosphate cathode material with excellent performance, and effectively solves the technical problems of poor performance of lithium iron phosphate prepared in the prior art, low solid content of slurry in the preparation process, insufficient drying of a precursor, high preparation cost and great pollution.
Specifically, aiming at the defects of the prior art, the invention provides the following technical scheme:
a preparation method of a high-density lithium iron phosphate positive electrode material comprises the following steps:
A. mechanical activation: firstly, weighing reducing iron powder and ferric orthophosphate according to a certain proportion, and uniformly mixing the weighed reducing iron powder and ferric orthophosphate to obtain a composite iron source; then adding a certain amount of deionized water into ball milling equipment, adding a lithium source, a composite iron source, a phosphorus source, a carbon source and a surfactant according to a certain proportion, and forming slurry after ball milling;
B. solid-liquid separation: b, pumping the slurry obtained in the step A into a membrane filter press for solid-liquid separation to obtain a filter cake-shaped precursor with the solid content of more than 85%;
C. and (3) flash evaporation drying: putting the precursor obtained in the step B into a flash dryer for drying to obtain a powdery precursor;
D. dynamic sintering: and sintering the precursor powder in a kiln with protective atmosphere, cooling, and then performing jet milling to obtain the lithium iron phosphate powder.
Preferably, the particle size D50 of the reducing iron powder in the composite iron source is 1 to 2 μm, the primary particle of ferric orthophosphate is 50 to 200nm, and the mixing molar ratio of the reducing iron powder to the ferric orthophosphate is 1: 10-1: 1, preferably 1: 5-1: 1.
preferably, in the step a, the ball milling time is 4-8 hours, the solid content of the slurry obtained by ball milling is 52-68%, the particle size of the slurry is controlled to be 1.0-2.0 μm, and the ratio of Li: fe: the molar ratio of P is (1-1.2): (0.96-1.2): 1.
preferably, the liquid content of the precursor after flash drying in step C is less than 1%.
Preferably, the weight of the carbon source added in the step A is 8-12% of the theoretical generation amount of the lithium iron phosphate, and the addition amount of the surfactant is 8-20% of the addition amount of the lithium source.
Preferably, the lithium source in step a is selected from one or more of lithium carbonate, lithium stearate and lithium dihydrogen phosphate; the phosphorus source is selected from lithium dihydrogen phosphate and/or ferric orthophosphate in a composite iron source, and the carbon source is selected from one or more of lithium stearate, magnesium stearate, stearic acid, glucose and phenolic resin; the surfactant is one or more selected from cetyl trimethyl ammonium bromide, polysorbate, alkylphenol polyoxyethylene and fatty alcohol polyoxyethylene.
Preferably, the protective atmosphere in step D is selected from one or more of nitrogen, argon and helium.
Preferably, the sintering in the step D is divided into two sections of high-temperature calcination, wherein the first section is calcined at the constant temperature of 400-500 ℃ for 2-4 hours, and the second section is calcined at the heat preservation of 650-800 ℃ for 6-10 hours.
Preferably, the particle size D50 of the lithium iron phosphate powder obtained by crushing in the step D is controlled to be 1.5-4 um, the D90 is controlled to be less than 12um, and the carbon content is controlled to be 1.4 +/-0.3 wt%.
The invention also provides a lithium iron phosphate anode material which is prepared by the preparation method.
Compared with the prior art, the invention has the advantages that:
(1) the composite iron source is obtained by mixing the reducing iron powder with the particle size D50 of 1-2 microns and the ferric orthophosphate with primary particles of 50-200 nm according to a proportion, the iron powder has higher density, the lithium iron phosphate synthesized by the composite iron source has higher tap density compared with other raw materials, and the composite iron source has excellent electrochemical performance by matching with the nanoscale ferric orthophosphate, and meanwhile, the density of the lithium iron phosphate material can be further improved due to the grading of the large and small particles.
(2) The surfactant is added into the raw materials, so that the viscosity of the raw material mixture can be reduced, the solid content of the slurry after ball milling is high, the subsequent solid-liquid separation and drying operation is facilitated, and the production period is shortened. In addition, the surfactant can better promote the uniform distribution of particles and improve the electrochemical performance of the lithium iron phosphate cathode material.
(3) The liquid content of precursor powder obtained by flash evaporation drying is low, the problem of precursor hollow spheres obtained by spray drying is solved, the obtained precursor is high-density spherical or irregular spherical particles, and the lithium iron phosphate anode material prepared from the precursor is excellent in electrochemical performance.
(4) The invention has the characteristics of continuous production process, uniform product property and stable quality, and the process is simple and feasible and is suitable for industrial production.
Drawings
FIG. 1 is an electron micrograph (SEM) of the lithium iron phosphate powder prepared in example 1;
FIG. 2 is an SEM image of the lithium iron phosphate powder prepared in example 2;
fig. 3 is an SEM image of the lithium iron phosphate powder prepared in comparative example 1.
Detailed Description
The invention provides a preparation method of a high-density lithium iron phosphate positive electrode material, which comprises the following steps:
A. mechanical activation: adding a certain amount of deionized water into ball milling equipment, and then adding a lithium source, a composite iron source, a phosphorus source, a carbon source and a surfactant in proportion, wherein the weight ratio of Li: fe: the molar ratio of P is (1-1.2): (0.96-1.2): 1, the weight of the carbon source is 8-12 wt% of the theoretical generation amount of the lithium iron phosphate, and the weight of the surfactant is 8-20 wt% of the addition amount of the lithium source; the composite iron source is obtained by mixing reduced iron powder with the D50 of 1-2 microns and ferric orthophosphate with primary particles of 50-200 nm according to the molar ratio of 1: 10-1: 1 (preferably 1: 5-1: 1), and forming mixed slurry after high-speed ball milling for 4-8 hours, wherein the solid content of the slurry is 52-68%;
B. solid-liquid separation: pumping the obtained slurry into a diaphragm filter press by using a diaphragm pump for solid-liquid separation to obtain a filter cake-shaped precursor with the solid content of more than 85 percent;
C. and (3) flash evaporation drying: placing the filter cake-shaped precursor obtained in the step B into a flash evaporation dryer for drying to obtain a powdery precursor with the liquid content of less than 1%;
D. dynamic sintering: and sintering the precursor powder in a kiln with protective atmosphere, wherein the sintering is divided into two sections, the first section is calcined at 400-500 ℃ for 2-4 hours, and the second section is calcined at 650-800 ℃ for 6-10 hours. After calcining, naturally cooling the material to room temperature, and then performing jet milling to obtain lithium iron phosphate powder, wherein the particle size D50 of the lithium iron phosphate powder is controlled to be 1.5-4 um, the D90 is less than 12um, and the carbon content is controlled to be 1.4 +/-0.3 wt%.
The lithium iron phosphate anode material prepared by the method has high density, and the battery prepared by the anode material has high capacitance.
The present invention is illustrated by the following specific examples. The reagents and equipment used in the present invention are commercially available.
Example 1
Ferric orthophosphate (FePO) with a primary particle size of 50nm4)300.00 kg of the iron powder is mixed with 11.14 kg of metal iron powder with the particle size D50 of 2um to obtain a composite iron source, 400 kg of deionized water is added into a ball mill, 73.52 kg of lithium carbonate, the composite iron source, 20.68 kg of lithium dihydrogen phosphate, 41.47 kg of stearic acid and hexadecyl as a surfactant are addedAnd (3) placing 18.84 kg of trimethyl ammonium bromide into a ball mill, and carrying out ball milling to prepare slurry, wherein the ball milling time is 4 hours, and the particle size of the slurry is controlled to be 1.5 microns, so that homogeneous mixed slurry with the solid content of 65% is obtained. Then pumping the ball-milled slurry into a diaphragm type filter press by using a diaphragm pump for filter pressing, wherein the filter pressing time is 1.5 hours, and obtaining a precursor with the water content of below 15%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, the air outlet temperature is 70 ℃, and precursor powder with the water content of 0.8% is obtained after drying; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering system is two-stage high-temperature calcination, the first stage is 500 ℃, and the constant temperature time is 2 hours; the second stage is 740 ℃, and the heat preservation and sintering are carried out for 10 hours; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 1.28g/cm3Powder compacted density of 2.75g/cm3The carbon content was 1.42%, and the specific surface area was 12.65g/m2The particle size D50 was 2.52 μm, D90 was less than 12 μm. Fig. 1 is an SEM image of the lithium iron phosphate powder prepared in this example, and it can be seen from the SEM image that the surface of the material is round and smooth, the particle size distribution is uniform, and the subsequent processability of the material is improved.
Test experiments:
the lithium iron phosphate powder material prepared in example 1 was subjected to a charge and discharge test under the following half-cell test conditions: the test of the battery is carried out at room temperature (25 ℃), and the test voltage is 2.5-4.0 v; the positive plate is prepared as follows: NMP (N-2-methyl pyrrolidone) is used as a solvent and a dispersing agent, 80% (mass ratio) of the prepared lithium iron phosphate powder positive electrode material, 10% of super P (super conductive carbon black) and 10% of an adhesive (polyvinylidene fluoride and PVDF) are uniformly mixed to prepare slurry, the solid content of the slurry is 45%, then the slurry is coated on an aluminum foil with the thickness of 20 mu m to prepare a film, and the film is dried in vacuum at 120 ℃ and then punched into a 10mm sheet to prepare a positive electrode sheet. A lithium metal sheet is used as a negative electrode, a Celgard 2400 membrane (a commercially available membrane) is used as a membrane, and an electrolyte is 1mol/L LiPF6(EC + DME), assembled in a glove box filled with high purity argon to give a simulated half cell. The prepared half cell was subjected to charge and discharge tests, and the results were obtainedIt was found that the half-cell capacity was 161.3mAh/g at 0.2C and 151.6mAh/g at 1C.
Example 2
Ferric orthophosphate (FePO) with primary particle size of 100nm4)150.00 kg of the iron source is mixed with 11.14 kg of metal iron powder with the particle size D50 of 1um to obtain a composite iron source, 250 kg of deionized water is added into a ball mill, 44.33 kg of lithium carbonate, the composite iron source, 15.78 kg of stearic acid and 6.65 kg of hexadecyl trimethyl ammonium bromide are placed into the ball mill for ball milling to prepare slurry, the ball milling time is 6 hours, the particle size of the slurry is controlled to be 1.0 micron, and the homogeneous mixed slurry with the solid content of 60% is obtained. Then pumping the ball-milling slurry into a diaphragm filter press by using a diaphragm pump for filter pressing for 2.0 hours to obtain a precursor with the liquid content of 12%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, the air outlet temperature is 70 ℃, and precursor powder with the liquid content of 0.5% is obtained after drying; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering is divided into two sections of high-temperature calcination, the first section is 400 ℃, and the constant temperature time is 4 hours; the second section is at 800 ℃, and the sintering is carried out for 6 hours under the condition of heat preservation; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 1.32g/cm3Powder compacted density of 2.78g/cm3The carbon content is 1.30%, and the specific surface area is 12.31g/m2The particle size D50 was 2.64 μm, D90 was less than 12 μm. Fig. 2 is an SEM image of the lithium iron phosphate powder prepared in this example, and it can be seen from the SEM image that the surface of the material is round and smooth, the particle size distribution is uniform, and the subsequent processability of the material is improved.
At the same time, the lithium iron phosphate powder material prepared in example 2 was subjected to charge and discharge tests under the same half-cell test conditions as in example 1. The test result shows that the half-cell capacity is 157.8mAh/g at 0.2C and 148.1mAh/g at 1C.
Example 3
150.00 kg of ferric orthophosphate (FePO4) with the primary particle size of 200nm and 56.00 kg of metal iron powder with the particle size D50 of 1um are mixed to obtain a composite iron source, 200 kg of deionized water is added into a ball mill, and 38.64 kg of lithium carbonate, the composite iron source,And (3) placing 15.78 kg of lithium stearate and 4.35 kg of polysorbate in a ball mill, and carrying out ball milling to prepare slurry, wherein the ball milling time is 8 hours, and the particle size of the slurry is controlled to be 1.0 micron, so that the homogeneous mixed slurry with the solid content of 68% is obtained. Then pumping the ball-milling slurry into a diaphragm filter press by using a diaphragm pump for filter pressing for 2.0 hours to obtain a precursor with the liquid content of 15%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, the air outlet temperature is 70 ℃, and precursor powder with the liquid content of 0.5% is obtained after drying; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering is divided into two sections of high-temperature calcination, the first section is 450 ℃, and the constant temperature time is 4 hours; the second section is 650 ℃, and the sintering is carried out for 10 hours under the condition of heat preservation; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 1.18g/cm3Powder compacted density of 2.68g/cm3The carbon content is 1.37%, and the specific surface area is 12.70g/m2The particle size D50 was 2.26 μm and D90 was less than 12 μm.
At the same time, the lithium iron phosphate powder material prepared in example 3 was subjected to charge and discharge tests under the same half-cell test conditions as in example 1. The test result shows that the half-cell capacity is 154.2mAh/g at 0.2C and 146.5mAh/g at 1C.
Example 4
200.00 kg of ferric orthophosphate (FePO4) with the primary particle size of 200nm and 31.59 kg of metal iron powder with the particle size D50 of 1um are mixed to obtain a composite iron source, 350 kg of deionized water is added into a ball mill, 49.15 kg of lithium carbonate, the composite iron source, 66.38 kg of lithium dihydrogen phosphate, 12.12 kg of phenolic resin and 11.55 kg of polysorbate are placed into the ball mill and are ball-milled to prepare slurry, the ball-milling time is 5 hours, the particle size of the slurry is controlled to be 1.5 microns, and homogeneous mixed slurry with the solid content of 65% is obtained. Then pumping the ball-milling slurry into a diaphragm filter press by using a diaphragm pump for filter pressing for 1.5 hours to obtain a precursor with the liquid content of 10%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, and the air outlet temperature is 70 ℃; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering,the sintering is divided into two sections of high-temperature calcination, wherein the first section is 500 ℃, and the constant temperature time is 3 hours; the second section is 750 ℃, and the sintering is carried out for 8 hours under the condition of heat preservation; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 1.29g/cm3Powder compacted density of 2.77g/cm3The carbon content is 1.39%, and the specific surface area is 12.95g/m2The particle size D50 was 1.60 μm, D90 was less than 12 μm.
At the same time, the lithium iron phosphate powder material prepared in example 4 was subjected to charge and discharge tests under the same half-cell test conditions as in example 1. The test result shows that the half-cell capacity is 157.8mAh/g at 0.2C and 148.5mAh/g at 1C.
Example 5
Ferric orthophosphate (FePO) with primary particle size of 100nm4)200.00 kg of the iron source is mixed with 31.59 kg of metal iron powder with the particle size D50 of 2um to obtain a composite iron source, 300 kg of deionized water is added into a ball mill, 44.35 kg of lithium carbonate, the composite iron source, 18.94 kg of glucose and 8.87 kg of alkylphenol ethoxylate are placed into the ball mill for ball milling to prepare slurry, the ball milling time is 6 hours, the particle size of the slurry is controlled to be 1.5 microns, and the homogeneous mixed slurry with the solid content of 62% is obtained. Then pumping the ball-milling slurry into a diaphragm filter press by using a diaphragm pump for filter pressing for 2.0 hours to obtain a precursor with the liquid content of 10%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, the air outlet temperature is 70 ℃, and precursor powder with the liquid content of 0.6% is obtained after drying; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering is divided into two sections of high-temperature calcination, the first section is 400 ℃, and the constant temperature time is 4 hours; the second section is 760 ℃, and the sintering is carried out for 5 hours under the condition of heat preservation; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 1.31g/cm3Powder compacted density of 2.79g/cm3The carbon content was 1.43%, and the specific surface area was 11.97g/m2The particle size D50 was 3.50 μm, and D90 was less than 12 μm.
At the same time, the lithium iron phosphate powder material prepared in example 5 was subjected to charge and discharge tests under the same half-cell test conditions as in example 1. The test result shows that the half-cell capacity is 156.8mAh/g at 0.2C and 144.2mAh/g at 1C.
Comparative example 1
66.62 kg of lithium carbonate, 300 kg of ferric orthophosphate and 54.02 kg of lithium stearate are placed in a ball mill, and then 400 kg of deionized water is added for ball milling to prepare slurry, wherein the ball milling time is 2 hours, so that the homogeneous mixed slurry is obtained. Then pumping the ball-milled slurry into a diaphragm type filter press by using a diaphragm pump for filter pressing, wherein the filter pressing time is 1.0 hour, and obtaining a precursor with the water content of below 20%; then conveying the precursor into a flash evaporation dryer for drying and mixing, wherein the drying air inlet temperature is 150 ℃, and the air outlet temperature is 70 ℃; putting the precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering is divided into two sections of high-temperature calcination, the first section is 500 ℃, and the constant temperature time is 2 hours; the second stage is 740 ℃, and the heat preservation and sintering are carried out for 10 hours; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 0.83g/cm3Powder compacted density of 2.35g/cm3The carbon content was 1.72%, and the specific surface area was 14.65g/m2The particle size D50 was 3.5. mu.m. The same half-cell test conditions as in the example were used, and the results showed that the half-cell capacity was 164.5mAh/g at 0.2C and 154.8mAh/g at 1C. Fig. 3 is an SEM image of the lithium iron phosphate powder prepared in the comparative example, where the material has a large number of corners on the surface, and has a non-uniform particle size distribution, and agglomeration occurs significantly, which affects the subsequent processability of the material.
Comparative example 2
74.43 kg of lithium carbonate, 300 kg of ferric orthophosphate, 30 kg of stearic acid, 10 kg of phenolic resin and 9 kg of surfactant are placed in a ball mill, then 300 kg of deionized water is added for ball milling to prepare slurry, and the uniform mixed slurry is obtained after ball milling for 2 hours. Then pumping the ball-milling slurry into a diaphragm type filter press by using a diaphragm pump for filter pressing for 1.5 hours to obtain a precursor with the water content of 18%; then conveying the precursor into a spray dryer for drying and mixing; putting the dried precursor powder into a kiln with protective atmosphere nitrogen for sintering, wherein the sintering system is two-stage high-temperature calcination, the first stage is 400 ℃, and the constant temperature time is 4 hours; second oneThe section is 800 ℃, and the sintering is carried out for 6 hours under the condition of heat preservation; and naturally cooling to room temperature, and performing jet milling to obtain lithium iron phosphate powder. The tap density of the lithium iron phosphate is 0.94g/cm3The powder compacted density was 2.47g/cm3The carbon content was 1.15%, and the specific surface area was 11.8g/m2The particle size D50 was 3.6. mu.m. The half-cell test conditions were the same as in the example, and the results showed that the half-cell capacity was 160.5mAh/g at 0.2C and 149.2mAh/g at 1C.
The morphological characteristic data of the lithium iron phosphate powder prepared in the comparative examples and the electrochemical performance parameters of the corresponding half-cell show that the lithium iron phosphate anode material prepared by the preparation method has moderate carbon content and good conductivity; the lithium iron phosphate anode material has high tap density and compaction density while ensuring the capacitance, and is beneficial to subsequent processing.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.

Claims (12)

1. The preparation method of the high-density lithium iron phosphate cathode material is characterized by comprising the following steps of:
A. mechanical activation: firstly, weighing reducing iron powder and ferric orthophosphate according to a certain proportion, and uniformly mixing the weighed reducing iron powder and ferric orthophosphate to obtain a composite iron source; then adding a certain amount of deionized water into ball milling equipment, adding a lithium source, a composite iron source, a phosphorus source, a carbon source and a surfactant according to a certain proportion, and forming slurry after ball milling;
B. solid-liquid separation: b, pumping the slurry obtained in the step A into a membrane filter press for solid-liquid separation to obtain a filter cake-shaped precursor with the solid content of more than 85%;
C. and (3) flash evaporation drying: putting the precursor obtained in the step B into a flash dryer for drying to obtain a powdery precursor;
D. dynamic sintering: sintering the precursor powder in a kiln with protective atmosphere, cooling, and then performing jet milling to obtain lithium iron phosphate powder;
the particle size D50 of the reducing iron powder in the composite iron source is 1-2 mu m, the primary particle of ferric orthophosphate is 50-200 nm, and the mixing molar ratio of the reducing iron powder to the ferric orthophosphate is 1: 10-1: 1.
2. the method for preparing the lithium iron phosphate positive electrode material according to claim 1, wherein the mixing molar ratio of the reducing iron powder to the ferric orthophosphate in the composite iron source is 1: 5-1: 1.
3. the preparation method of the lithium iron phosphate positive electrode material according to claim 1 or 2, wherein in the step a, the ball milling time is 4-8 hours, the solid content of the slurry obtained by ball milling is 52-68%, the particle size of the slurry is controlled to be 1.0-2.0 μm, and the ratio of Li: fe: the molar ratio of P is (1-1.2): (0.96-1.2): 1.
4. the method for preparing a lithium iron phosphate positive electrode material according to claim 3, wherein the liquid content of the precursor after flash drying in the step C is less than 1%.
5. The method for preparing a lithium iron phosphate positive electrode material according to claim 1 or 2, wherein the weight of the carbon source added in the step a is 8-12% of the theoretical production amount of lithium iron phosphate, and the addition amount of the surfactant is 8-20% of the addition amount of the lithium source.
6. The method for preparing the lithium iron phosphate cathode material according to claim 3, wherein the weight of the carbon source added in the step A is 8-12% of the theoretical production amount of the lithium iron phosphate, and the addition amount of the surfactant is 8-20% of the addition amount of the lithium source.
7. The method for preparing the lithium iron phosphate cathode material according to claim 4, wherein the weight of the carbon source added in the step A is 8-12% of the theoretical production amount of the lithium iron phosphate, and the addition amount of the surfactant is 8-20% of the addition amount of the lithium source.
8. The method for preparing the lithium iron phosphate cathode material according to claim 5, wherein the lithium source in the step A is one or more selected from lithium carbonate, lithium stearate and lithium dihydrogen phosphate; the phosphorus source is selected from lithium dihydrogen phosphate and/or ferric orthophosphate in a composite iron source, and the carbon source is selected from one or more of lithium stearate, magnesium stearate, stearic acid, glucose and phenolic resin; the surfactant is one or more selected from cetyl trimethyl ammonium bromide, polysorbate, alkylphenol polyoxyethylene and fatty alcohol polyoxyethylene.
9. The method for preparing the lithium iron phosphate cathode material according to claim 8, wherein the protective atmosphere in step D is selected from one or more of nitrogen, argon and helium.
10. The method for preparing the lithium iron phosphate cathode material according to claim 9, wherein the sintering in step D is divided into two stages of high-temperature calcination, the first stage is constant-temperature calcination at 400-500 ℃ for 2-4 hours, and the second stage is constant-temperature calcination at 650-800 ℃ for 6-10 hours.
11. The method for preparing a lithium iron phosphate positive electrode material according to claim 10, wherein the particle size D50 of the lithium iron phosphate powder obtained by crushing in step D is controlled to be 1.5 to 4um, the particle size D90 is controlled to be less than 12um, and the carbon content is controlled to be 1.4 ± 0.3 wt%.
12. A lithium iron phosphate positive electrode material characterized by being produced by the production method according to any one of claims 1 to 11.
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