CN111540901A - Method for preparing lithium iron phosphate (LEP) by using lithium iron (III) phosphate - Google Patents
Method for preparing lithium iron phosphate (LEP) by using lithium iron (III) phosphate Download PDFInfo
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Abstract
A process for preparing lithium iron phosphate (LEP) from lithium iron (III) phosphate by Li3Fe2(PO4)3And the molar ratio of iron in the iron source is = (1.01-1.05): 1, and the raw materials are mixed, and simultaneously, the carbon source and the doped metal oxide are mixed according to 8-15% of the total mixture amount to obtain the mixture; adding the ingredients into a ball mill for ball milling, removing iron by using a permanent magnet in the ball milling process, conventionally drying the material after iron removal, and sintering under the protection of inert gas, wherein the sintering system comprises a conversion temperature of 430-470 ℃, a correction temperature of 720-780 ℃, and a curing temperature of 640-680 DEG CAnd then cooling to below 95 ℃ and discharging, and then obtaining a lithium iron phosphate product through conventional crushing and packaging. The method has the advantages of short process flow, and the obtained iron phosphate has the characteristics of good product uniformity, high purity and the like and has excellent electrical property.
Description
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to a method for preparing lithium iron phosphate (LEP) by using lithium iron phosphate (III).
Background
Lithium iron phosphate (LiFePO)4LFP for short) is used as the anode material of the lithium ion battery, the theoretical specific capacity is 170 mAh.g < -1 >, the actual specific capacity exceeds 140 mAh.g < -1 > (0.2C, 25 ℃), and the lithium ion battery has the advantages of low price, good thermal stability, environmental protection, high safety and excellent cycle performance. At present, lithium iron phosphate is widely applied to the fields of electric buses, special vehicles and the like, the price of the lithium iron phosphate drops to 5 ten thousand along with the drop of the price of lithium carbonate, but the preparation of lithium batteries is still expensive, and the lithium batteries have strong competitiveness only when the price of 1WH of the lithium batteries is lower than 0.8 yuan in the future, so that the performance of the lithium iron phosphate needs to be improved, and the price of the lithium iron phosphate needs to be continuously reduced.
At present, the existing technology for preparing lithium iron phosphate by using low-temperature lithiation iron phosphate needs to use an organic solvent (such as absolute ethyl alcohol) and the mother solution is difficult to recycle, thereby causing waste. Meanwhile, most of lithium source-lithium-containing compounds used for lithiation in the preparation methods are simple inorganic substances, the solubility in organic solvents is not high, the solvent amount is large during mass preparation, heating is needed, the energy consumption is high, and the cost is high.
The patent CN 102104149A discloses a lithium iron phosphate composite anode material in a lithium ion battery and a preparation method thereof, the invention adopts raw materials containing lithium, iron and phosphorus to prepare lithium iron phosphate, then the lithium iron phosphate is uniformly mixed with nanowires, and the nanowire composite lithium iron phosphate anode material is prepared by annealing, so that the nanowire composite lithium iron phosphate anode material has excellent conductivity, and improves the reversible capacity, the rate capability and the cycle life of the battery. GuoxiuWang et al, university of horizontal Dragon hillock, Canada, prepared a one-dimensional lithium iron phosphate nanowire which was not coated with carbon by a hydrothermal method in an article published by Journal of Power sources in 2008, and the specific capacity of the nanowire was up to 140mAh/g, which indicates that the shape control of the lithium iron phosphate has a positive effect on improving the performance of the battery; then, researchers successfully synthesize lithium iron phosphate nanorods, nanosheets, nanodiscs and the likeA nanostructure is provided. Researchers have doped the prepared lithium iron phosphate in an attempt to improve its physicochemical properties, such as "Effect of thermal treatment on the properties of electrospun LiFePO", published by Changhean Zhang et al, university of east China4The carbon nanafiber composite cathode materials for lithium-ion batteries uses a mixed solution of a lithium iron phosphate precursor and polyacrylonitrile as a reaction solution, a nanowire is prepared in an electrostatic spinning mode, and then the nanowire is subjected to two-stage heating and carbonization to obtain the lithium iron phosphate/C composite material which has better electrical property, the initial discharge capacity of the material at 0.5 ℃ is 146.3 mAh/g, and the material still has better stability after being circulated for 100 circles, which means that the electrical property of the doped lithium iron phosphate can be properly improved. The traditional preparation method of the lithium iron phosphate by the solid phase method or the liquid phase method is further characterized in that the performance of the product is improved to a certain extent by a nanowire composite technology or a doping means, the cost is overhigh due to multiple sintering, and the whole preparation process is complex and tedious.
At present, the synthesis technology of the lithium iron phosphate anode material has various process technical routes, and the industrialized technical routes include an iron oxide red route, a ferrous oxalate route, a hydrothermal synthesis route and an iron orthophosphate route. The lithium iron phosphate prepared by the ferric orthophosphate route has the advantages of good electrical property, low impurity content, relatively simple process steps and the like, and gradually becomes a technical trend of industry unification. However, the iron phosphate prepared in the prior art has the problems of purity fluctuation, undefined crystal structure and the like, and the obtained product lithium iron phosphate has the defects of poor processing effect and low electrochemical performance due to low compaction density, low tap density and high specific surface area, so that the lithium iron phosphate material with excellent performance is prepared by changing raw and auxiliary materials, improving the preparation process of the iron phosphate and optimizing technical conditions to overcome the defect of the lithium iron phosphate.
Disclosure of Invention
The invention aims to provide a method for preparing lithium iron phosphate (LEP) by using lithium iron (III) phosphate, aiming at the defects of the prior art, the preparation method can be used for preparing the lithium iron phosphate anode material only by one-time sintering, the process is simple, the flow is short, the cost is low, and the prepared lithium iron phosphate anode material has high compaction density, good crystallinity and excellent electrical property.
The technical scheme of the invention is as follows:
a method of preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate, comprising the steps of:
A. preparing materials: according to Li3Fe2(PO4)31, adding raw materials, adding a carbon source accounting for 8-15% of the total ingredient amount of the lithium iron phosphate (III) and the iron source according to the mass percent, and adding a doped metal oxide, wherein the mass percent of the doped metal oxide is 0.03-0.30% of the total ingredient amount of the lithium iron phosphate (III) and the iron source to form ingredients;
B. ball milling: and B, adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is (2.2-3.8): 1, and removing magnetic substances by using a permanent magnet during ball milling to obtain the material without the magnetic substances.
C. And (3) sintering: b, sintering the material subjected to magnetic substance removal obtained in the step B under the protection of inert gas after conventional drying, wherein the sintering system comprises the steps of converting lithium iron phosphate at the temperature of 430-;
as a further improvement of the invention, the carbon source in the step A comprises one or more of starch, glucose, sucrose, citric acid, polyethylene glycol and the like; the doped metal oxide includes one of aluminum oxide, magnesium oxide, and the like.
As a further improvement of the present invention, the iron source in step a includes ferrous oxide, ferric hydroxide, ferrous hydroxide, ferric carbonate, ferric oxalate, ferric acetate, etc. in addition to ferric oxide.
The doping material is added in the form of oxide, hydroxide, carbonate or organic salt, so that anions such as sulfate radicals and chloride ions are prevented from being brought into the lithium iron phosphate product, and the compaction density and the electrical property of the product are improved; the nitrogen oxides generated in the sintering process of nitrate ions are reduced, so that the environment is polluted, and the production cost is increased.
As a further improvement of the invention, the ball milling in the step B is divided into coarse milling and fine milling, the coarse milling and the fine milling are respectively subjected to permanent magnet iron removal, the material contains 0.35-0.45ppm of magnetic substances, and the particle size D50= 0.3-0.5 μm after the fine milling.
As a further improvement of the invention, the sintering schedule in the step C is as follows: firstly, heating from room temperature to 200 ℃ at a constant speed for 2h, and then heating from 200 ℃ to a conversion temperature at a constant speed for 4-6 h; then raising the temperature from the conversion temperature to 550 ℃ at a constant speed, wherein the temperature raising time is 3h, and then raising the temperature from 550 ℃ to the correction temperature at a constant speed, and the temperature raising time is 5-7 h; and then, uniformly cooling from the corrected temperature to the curing temperature for 5-6h, cooling to below 95 ℃, discharging, and performing conventional crushing and packaging to obtain a lithium iron phosphate product.
As a further improvement of the invention, in the step C, when the temperature is raised to the conversion temperature of 430-470 ℃, the temperature is kept for 5-8 h; when the temperature is increased to the correction temperature of 720-780 ℃, the temperature is kept for 8-12h, and when the temperature is reduced to the curing temperature of 640-680 ℃, the temperature is kept for 5-7 h; the cooling time is 15-20 h.
As a further optimization of the invention, in the stage of conversion temperature, the temperature is firstly raised to 450-470 ℃ and kept for 4-5h, and then is lowered to 430 ℃ and kept for 1-2 h; and then the temperature is raised to the correction temperature.
With Li3Fe2(PO4)3And Fe2O3The method for preparing lithium iron phosphate (LFP) by using + carbon source as raw material is carried out mechanism analysis, as shown in figure 1-Li3Fe2(PO4)3And Fe2O3FIG. 1 shows the thermogravimetric analysis of post-sintering of carbon + source, which is shown in FIG. 1: exothermic peak formed by lithium iron phosphate crystal form, namely Li3Fe2(PO4)3And Fe2O3The temperature for converting into the lithium iron phosphate (LFP) is 430-470 ℃, and the reaction belongs to an exothermic reaction; the thermogravimetric curve (representing the weight change of the material) shows that the lithium iron phosphate is perfect after 600 degrees of crystallization, and experimental research shows that the lithium iron phosphate is completely crystallizedThe good correction temperature is 720-780 ℃, and the finished lithium iron phosphate is solidified at 640-680 ℃, so that the obtained lithium iron phosphate has perfect crystal lattice, carbon is uniformly distributed among all particles to form compact carbon coating, the compaction density of the product can reach 2.6g/mL and is far higher than the conventional compaction density of 2.3g/mL, the BET of the product is controllable and is generally less than 18m2And the product has better processing performance.
In the sintering system in the step C, the inert gas comprises: nitrogen, helium, neon, and the like; controlling the oxygen concentration to be 10-100ppm and the micro-positive pressure in the furnace to be 10-100 Pa; and (4) after the material is discharged from the furnace, conventionally crushing and packaging the material to obtain a lithium iron phosphate product.
In the ball milling process, lithium iron phosphate (III), iron oxide and a carbon source are fully mixed by adopting a dispersant sodium dodecyl benzene sulfonate, so that the agglomeration of the iron oxide which is easy to generate colloidal materials is avoided, the crystallization purity of the lithium iron phosphate is higher, the crystal lattice is more perfect, and the electrochemical performance of the product is improved; magnetic iron removal is carried out in the ball milling stage, at the moment, the material granularity is finer, the wrapping around the magnetic substance is removed as much as possible, the removal of the magnetic substance is more thorough and is close to half of the content of like products in the existing market, meanwhile, the special iron removal process is reduced, and the production cost is reduced; meanwhile, ball-milling and drying processes are used for ball-shaped granulation, so that the tap density and the compaction density are increased, and the energy density in unit volume is higher; the sintering system process comprises the stages of converting temperature, correcting temperature and curing temperature, the ferric phosphate iron crystal lattice is complete, the carbon coating is more complete, the Li ion migration rate is rapidly improved, and the electrochemical performance is more excellent.
The invention has the beneficial effects that:
1. the raw materials of the invention are lithium iron (III) phosphate and ferric oxide, certainly include a defective lithium iron phosphate (LFP) raw material which can generate the lithium iron (III) phosphate and ferric oxide by a certain technical means, and simultaneously include a purer lithium iron phosphate anode material which is disassembled from the lithium iron phosphate battery and separated. Therefore, with the coming of the charge reporting period of a large number of lithium iron phosphate batteries, the lithium iron phosphate batteries have wide raw materials, and the project belongs to the field of green and environment-friendly circular economy.
2. The magnetic material is removed more thoroughly by magnetic iron removal in the ball milling stage, and the iron removal process is reduced; the spray granulation and sintering process carries out compact carbon coating on the lithium iron phosphate through three stages of conversion temperature, correction temperature and curing temperature, carbon is uniformly distributed among particles, the defects of the lithium iron phosphate are prevented, the purity of the product lithium iron phosphate is ensured, and by the technology, the lithium iron phosphate material with high conductivity and low internal resistance can be obtained, and the electrical property is excellent. The lithium iron phosphate prepared by the process can be compacted to 2.5-2.6g/mL, the 1C discharge capacity exceeds 142mAh/g, the normal-temperature circulation can reach 3000 circles, and the performance of the lithium iron phosphate is equivalent to that of the medium-high-end lithium iron phosphate on the market. Can be well applied to the energy storage industry and the power battery industry.
3. The invention is particularly applied to the raw materials of the waste lithium iron phosphate positive electrode material, has the advantages of reasonable process, low manufacturing cost, environmental protection, no toxicity and the like, has the electrochemical performance meeting the requirements of olivine type lithium iron phosphate batteries sold in the market, and has very wide application prospect.
Drawings
FIG. 1 Li3Fe2(PO4)3And Fe2O3Thermogravimetric analysis of post-sintering of + carbon source
FIG. 2 is Li3Fe2(PO4)3With Fe2O3XRD pattern after ball milling and drying
Fig. 3 is a 0.2C charging and discharging curve diagram of the lithium iron phosphate cathode material prepared in the embodiment 1
Fig. 4 is a 1C cycle curve diagram of the lithium iron phosphate cathode material prepared in this embodiment 1
Fig. 5 is a graph illustrating the cycle performance of the repaired lithium iron phosphate positive electrode material in this embodiment 4
Fig. 6 is a graph showing rate performance of the repaired lithium iron phosphate positive electrode material of this example 5
FIG. 7 is a process flow diagram of the present invention.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It is to be understood that the specific examples described herein are merely illustrative of the present invention and are not intended to limit the present invention, and the present invention encompasses other embodiments and modifications thereof within the scope of the technical spirit thereof.
In the present invention, Li is sometimes added depending on the material3Fe2(PO4)3The preparation steps of the method can be reduced, or the steps of magnetic iron removal and the like can be reduced, or the step of screening lithium iron phosphate can be added, but the method can also be applied as long as the basic process flow is not changed.
An embodiment of the present invention provides a method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate, please refer to fig. 6. The invention is further illustrated by the following specific examples.
Example 1
Step A, mixing materials according to Li3Fe2(PO4)3With Fe2O3The molar ratio of the medium iron is 1.01:1, and Li is added3Fe2(PO4)3With Fe2O3Preparing raw materials, and simultaneously taking Li in percentage by mass3Fe2(PO4)3With Fe2O3Adding starch in 15% of the total mass of the raw materials, and adding aluminum oxide, wherein the mass percent of the aluminum oxide is Li3Fe2(PO4)3With Fe2O30.30% of the total mass of (a).
And B, ball milling, namely adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is 2.2:1, adding 0.02g/L anionic dispersant sodium dodecyl benzene sulfonate, and removing iron by using a permanent magnet in the process, wherein the content of magnetic substances in the ball-milled materials is 0.35ppm, and the particle size D50=0.3 mu m.
Step C, sintering, namely sintering the materials except the magnetic substances obtained in the step B under the protection of nitrogen after conventional drying, wherein the temperature is uniformly increased at the temperature stage of each liter, the time of 200 ℃ at room temperature is 2 hours, the time of reaching the conversion temperature is 4 hours, the conversion temperature is 470 ℃, and the constant temperature is 5 hours; the time of reaching 550 ℃ is 3 hours, the time of reaching the correction temperature is 5 hours, the correction temperature is 720 ℃, the constant temperature time is 12 hours, the time of cooling to the solidification temperature after the correction temperature is 5 hours, the solidification temperature is 680 ℃, the constant temperature time is 5 hours, the time of cooling for a period is 20 hours, and the furnace is discharged at 95 ℃; the oxygen concentration is controlled to be 100ppm in the whole sintering process, and the micro-positive pressure in the furnace is controlled to be 100 Pa.
And D, performing conventional crushing and packaging on the discharged materials in the step C to obtain the following indexes of the lithium iron phosphate:
the iron phosphate lithium index of the product and the 1C cycle curve chart of figure 4 show that the compaction density is higher than that of an LFP product in the conventional market by 2.3g/mL, the first efficiency of 0.1C is far more than 95%, the first discharge of 1C reaches 151 mAh/g, the cycle efficiency of 2000 times reaches 92.3%, the first discharge of 1C is far more than 85% required by a common manufacturer, and the magnetic material reaches half of the requirement of the conventional manufacturer.
Example 2
Step A, mixing materials according to Li3Fe2(PO4)3And Fe2(C2O4)3· 5H2The raw materials are added according to the molar ratio of O =1.05:1, meanwhile, polyethylene glycol accounting for 8% of the total amount of the raw materials is added according to the mass percentage, and the aluminum oxide accounting for 0.03% of the mass percentage is weighed.
And B, ball milling, namely adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the liquid-solid ratio in the ball milling process is 3.8:1, adding 0.08g/L anionic dispersant sodium dodecyl benzene sulfonate, removing iron by using a permanent magnet in the process, and the content of magnetic substances in the ball-milled materials is 0.45ppm and the particle size D50=0.5 mu m.
Step C, sintering, namely sintering the material except the magnetic substances obtained in the step B under the protection of helium after conventional drying, wherein the temperature is uniformly increased in each liter of temperature stage, the time from room temperature to 200 ℃ is 2 hours, the time from the room temperature to the conversion temperature is 6 hours, the conversion temperature is 430 ℃, and the constant temperature time is 8 hours; the time of reaching 550 ℃ is 3 hours, the time of reaching the correction temperature is 7 hours, the correction temperature is 780 ℃, the constant temperature time is 8 hours, the time of cooling to the solidification temperature after the correction temperature is 6 hours, the solidification temperature is 640 ℃, the constant temperature time is 7 hours, the cooling time is 15 hours, and the product is discharged at 90 ℃; the oxygen concentration is controlled to be 10ppm in the whole sintering process, and the micro-positive pressure in the furnace is controlled to be 10 Pa.
And D, performing conventional crushing and packaging on the discharged materials in the step C to obtain the following indexes of the lithium iron phosphate:
the indexes of the product lithium iron phosphate show that the compaction density is higher than that of an LFP product on the conventional market by 2.3g/mL, the first efficiency of 0.1C is far more than 95%, the first discharge of 1C reaches 153 mAh/g, the cycle efficiency of 2000 times reaches 91.5%, the first discharge of 1C is far more than 85% of that of a common manufacturer, and the magnetic substance reaches half of that of the conventional manufacturer.
Example 3
Step A, mixing materials according to Li3Fe2(PO4)3The raw materials are mixed with FeO according to the mol ratio =1.03:2, glucose is mixed according to the mass percent accounting for 11 percent of the total mixture amount, and the magnesium oxide with the mass percent accounting for 0.20 percent is weighed.
And B, ball milling, namely adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is 2.8:1, a permanent magnet is used for removing iron during ball milling, the content of magnetic substances in the materials after ball milling is 0.40ppm, and the particle size D50= 0.4 μm.
Step C, sintering, namely drying the materials of the demagnetizing substances obtained in the step B in a conventional manner, sintering under the protection of neon, and uniformly heating at a constant speed at a temperature of each liter, wherein the time from room temperature to 200 ℃ is 2 hours, the time from the room temperature to the conversion temperature is 5 hours, the conversion temperature is 450 ℃, and the constant temperature is 6 hours; the time of reaching 550 ℃ is 3 hours, the time of reaching the correction temperature is 6 hours, the correction temperature is 750 ℃, the constant temperature time is 10 hours, the time of cooling to the solidification temperature after the correction temperature is 5.5 hours, the solidification temperature is 660 ℃, the constant temperature time is 6 hours, then the cooling time is 18 hours, and the furnace is discharged at 85 ℃; the oxygen concentration is controlled to be 50ppm in the whole sintering process, and the micro-positive pressure in the furnace is controlled to be 30 Pa.
And D, performing conventional crushing and packaging on the discharged materials in the step C to obtain the following indexes of the lithium iron phosphate:
the indexes of the product lithium iron phosphate show that the compaction density is higher than that of an LFP product on the conventional market by 2.3g/mL, the first efficiency of 0.1C is far more than 95%, the first discharge of 1C reaches 154 mAh/g, the cycle efficiency of 2000 times reaches 92.0%, the first discharge of 1C is far more than 85% of that of a common manufacturer, and the magnetic substance reaches half of that of the conventional manufacturer.
Example 4
Step A, roasting, namely detecting the components of the lithium iron phosphate secondary powder generated in the purchased production process, wherein the molar ratio of P to Fe to Li =1:1.02:1.04, and the rest impurities are as follows: roasting the detected lithium iron phosphate secondary powder with trace Al, Mg, Ca and the like to obtain Li3Fe2(PO4)3And Fe2O3And (3) mixing.
And step B, mixing, namely adding cane sugar into the mixture obtained in the step A according to the mass percentage accounting for 12% of the total mixture amount, and weighing magnesium oxide with the mass percentage of 0.15%.
And C, ball milling, namely adding the ingredients obtained in the step B into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is 2.6:1, a permanent magnet is used for removing iron during ball milling, the content of magnetic substances in the ball-milled materials is 0.41ppm, and the particle size D50=0.35 μm.
D, sintering, namely sintering the materials except the magnetic substances obtained in the step C under the protection of nitrogen after conventional drying, wherein the temperature is uniformly increased in each liter of temperature stage, the time from the room temperature to 200 ℃ is 2 hours, the time from the room temperature to the conversion temperature is 4.5 hours, the conversion temperature is 460 ℃, and the constant temperature time is 6 hours; the time of reaching 550 ℃ is 3 hours, the time of reaching the correction temperature is 5.5 hours, the correction temperature is 740 ℃, the constant temperature time is 9 hours, the time of cooling to the solidification temperature after the correction temperature is 5.2 hours, the solidification temperature is 670 ℃, the constant temperature time is 5.5 hours, then the cooling time is 16 hours, and the furnace is discharged at 92 ℃; the oxygen concentration is controlled to be 80ppm in the whole sintering process, and the micro-positive pressure in the furnace is controlled to be 40 Pa.
And D, performing conventional crushing and packaging on the discharged materials in the step C to obtain the following indexes of the lithium iron phosphate:
the indexes of the lithium iron phosphate product and the 1C cycle curve chart of figure 5 show that the compaction density is higher than that of an LFP product in the conventional market by 2.3g/mL, the first efficiency of 0.1C is far more than 95%, the first discharge of 1C reaches 151 mAh/g, the cycle efficiency of 2000 times reaches 92.1%, the first discharge of 1C is far more than 85% required by a common manufacturer, and the magnetic material reaches half of the requirement of the conventional manufacturer; no matter from the evaluation of the processing performance of the product or the evaluation of the electrochemical capacity of the product, the product is better than the product of patent 2018108877359, and the electrochemical capacity of the product performance 1C produced by patent 2018108877359 is about 145 mAh/g.
Example 5
Step A, roasting, namely performing component detection on waste lithium iron phosphate powder which is disassembled from waste lithium iron phosphate batteries from different factories, has different defects and different particle sizes, wherein the molar ratio of P to Fe to Li is =1:0.96:0.75, and the rest impurities are as follows: the contents of Al and F are respectively 0.41% and 0.28%, iron carbonate and lithium carbonate are added into the detected waste lithium iron phosphate powder according to the molar ratio of P: Fe: Li =1:1:1.03, and the mixture is roasted after ball milling to obtain Li3Fe2(PO4)3And Fe2O3And (3) mixing.
And step B, mixing materials, namely mixing sucrose into the mixture obtained in the step A according to the mass percentage accounting for 12 percent of the total mixture.
And C, ball milling, namely adding the ingredients obtained in the step B into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is 3.2:1, a permanent magnet is used for removing iron during ball milling, the content of magnetic substances in the ball-milled materials is 0.39ppm, and the particle size D50=0.36 μm.
D, sintering, namely sintering the material except the magnetic substances obtained in the step C under the protection of nitrogen after conventional drying, wherein the temperature is uniformly increased at the temperature stage of each liter, the time of 200 ℃ at room temperature is 2 hours, the time of reaching the conversion temperature is 4.8 hours, the conversion temperature is 460 ℃, and the constant temperature time is 5.8 hours; the time of reaching 550 ℃ is 3 hours, the time of reaching the correction temperature is 6.2 hours, the correction temperature is 762 ℃, the constant temperature time is 11 hours, the time of cooling to the solidification temperature after the correction temperature is 5.2 hours, the solidification temperature is 666 ℃, the constant temperature time is 6.3 hours, then the cooling time is 17.8 hours, and the furnace is discharged at the temperature of below 94 ℃; the whole sintering process controls the oxygen concentration to be 60ppm and the micro-positive pressure in the furnace to be 70 Pa.
And D, performing conventional crushing and packaging on the discharged materials in the step D to obtain the following indexes of the lithium iron phosphate:
the iron phosphate lithium index and rate performance curve diagram of the product shows that the compaction density is higher than that of an LFP product in the conventional market by 2.3g/mL, the first efficiency of 0.1C is far more than 95%, the first discharge of 1C reaches 146mAh/g, the cycle efficiency of 2000 times reaches 90.7%, the first discharge of 1C is far more than 85% of that of a common manufacturer, and the magnetic material reaches half of that of the conventional manufacturer; no matter from the evaluation of the processing performance of the product or the evaluation of the electrochemical capacity of the product, the product is superior to patent 2018108877359, and particularly when the lithium iron phosphate waste contains a certain amount of impurities Cu and F, the product performance, particularly the electrochemical capacity of 1C, produced by patent 2018108877359 is below 135 mAh/g, so that the product performance produced by the method is more excellent, and the adaptability of the raw material is wider; meanwhile, the content of F in the product is obviously lower than that of F in the raw materials, and the method also has the function of removing impurities.
Meanwhile, the method fundamentally solves the problem of consistency of products obtained after the lithium iron phosphate waste powder is repaired, which is difficult to solve by other methods.
In the embodiment, waste lithium iron phosphate powder with the contents of Al and F impurities of 0.41% and 0.28% respectively separated from waste lithium iron phosphate batteries is pretreated to obtain Li3Fe2(PO4)3And Fe2O3The obtained product lithium iron phosphate cathode material is prepared, the multiplying power performance curve diagram of which is shown in fig. 6, and the multiplying power performance can be obtained from fig. 5: 0.2-150.7 mAh/g, 0.5-148.3 mAh/g, 1C-144.3mAh/g, 2C-137.3mAh/g, 5C-123.7 mAh/g. Meanwhile, the invention also shows that the invention has stronger adaptability and can be popularized and applied.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included therein.
Claims (8)
1. A method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate, comprising the steps of:
A. preparing materials: according to Li3Fe2(PO4)31, adding raw materials, adding a carbon source accounting for 8-15% of the total ingredient amount of the lithium iron phosphate (III) and the iron source according to the mass percent, and adding a doped metal oxide, wherein the mass percent of the doped metal oxide is 0.03-0.30% of the total ingredient amount of the lithium iron phosphate (III) and the iron source to form ingredients;
B. ball milling: b, adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the liquid-solid ratio during ball milling is (2.2-3.8): 1, and removing magnetic substances by using a permanent magnet during ball milling to obtain a material without the magnetic substances;
C. and (3) sintering: and D, sintering the material subjected to the magnetic substance removal in the step B under the protection of inert gas after conventional drying, wherein the sintering system comprises the steps of converting the lithium iron phosphate at the temperature of 430-.
2. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, wherein: in the step A, the carbon source is one or more of starch, glucose, sucrose, citric acid and polyethylene glycol; the doped metal oxide is one of aluminum oxide and magnesium oxide.
3. A method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, wherein: in the step A, the iron source is one or more of ferric oxide, ferrous oxide, ferric hydroxide, ferrous hydroxide, ferric carbonate, ferric oxalate and ferric acetate.
4. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, wherein: and B, performing ball milling in the step B, wherein the ball milling is divided into coarse milling and fine milling, the coarse milling and the fine milling are respectively used for removing magnetic substances by using a permanent magnet, so that the content of magnetic substances in the material is controlled to be 0.35-0.45ppm, and the grain diameter D50 of the material after the fine milling is 0.3-0.5 mu m.
5. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, wherein: in the step C, the sintering system is that temperature is increased and decreased at constant speed in a segmented manner in each stage when the temperature changes, the time from room temperature to 200 ℃ is 2 hours, and the time from the room temperature to the conversion temperature is 4-6 hours; the time from the conversion temperature to 550 ℃ is 3h, and then the time to the correction temperature is 5-7 h; the time from the temperature correction to the solidification temperature is 5-6 h.
6. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1 or 5, wherein: and C, respectively keeping the conversion temperature, the correction temperature and the curing temperature for 5-8h, 8-12h and 5-7h, and then cooling for 15-20 h.
7. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 5, wherein: in the stage of conversion temperature, firstly raising the temperature to 450-470 ℃ and keeping the temperature for 4-5h, and then lowering the temperature to 430 ℃ and keeping the temperature for 1-2 h; and then the temperature is raised to the correction temperature.
8. The method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, wherein: in the sintering system in the step C, the inert gas is one of nitrogen, helium and neon; controlling the oxygen concentration to be 10-100ppm and the micro-positive pressure in the furnace to be 10-100Pa during sintering; and (4) after the material is discharged from the furnace, conventionally crushing and packaging the material to obtain a lithium iron phosphate product.
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