CN111540901B - Method for preparing lithium iron phosphate (LEP) by using lithium iron phosphate (III) - Google Patents
Method for preparing lithium iron phosphate (LEP) by using lithium iron phosphate (III) Download PDFInfo
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
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- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
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- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/37—Phosphates of heavy metals
- C01B25/375—Phosphates of heavy metals of iron
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- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
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- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M10/00—Secondary cells; Manufacture thereof
- H01M10/05—Accumulators with non-aqueous electrolyte
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- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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Abstract
A method for preparing lithium iron phosphate (LEP) by using lithium iron phosphate (III) according to Li 3 Fe 2 (PO 4 ) 3 And iron in iron source = (1.01-1.05), 1 adding raw material, at the same time adding carbon source and doped metal oxide according to 8-15% of total dosage to obtain the dosage; adding ingredients into a ball mill for ball milling, removing iron by using a permanent magnet in the ball milling process, conventionally drying the iron-removed material, sintering under the protection of inert gas, wherein the sintering system is divided into a conversion temperature of 430-470 ℃, a correction temperature of 720-780 ℃ and a solidification temperature of 640-680 ℃, cooling to below 95 ℃ and discharging from the furnace, and conventionally crushing and packaging to obtain a lithium iron phosphate product. The method has the characteristics of short process flow, good uniformity, high purity and the like of the obtained ferric phosphate, and has excellent electrical properties.
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) 4 Abbreviated as LFP) is used as a positive electrode material of the lithium ion battery, the theoretical specific capacity of the positive electrode material is 170mAh g < -1 >, the actual specific capacity exceeds 140mAh g < -1 > (0.2C, 25 ℃), and the positive electrode material 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 is reduced to 5 ten thousand along with the price reduction of lithium carbonate, but the preparation of a lithium battery is still more expensive, and only the lithium battery is manufactured to have the price of 1WH lower than 0.8 yuan in the future, the lithium iron phosphate has stronger competitiveness, so that the performance of the lithium iron phosphate is required to be improved, and the price is required to be continuously reduced.
At present, the existing technology for preparing lithium iron phosphate by adopting low-temperature lithiation of ferric phosphate requires an organic solvent (such as absolute ethyl alcohol and the like), and the mother solution is difficult to recycle and reuse, thus causing waste. Meanwhile, most of lithium sources-lithium-containing compounds used in the preparation methods are simple inorganic matters, the solubility in organic solvents is low, the amount of solvents needed in mass preparation is large, heating is needed, and the energy consumption and the cost are high.
Patent CN 102104149a discloses a lithium iron phosphate composite positive electrode 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 annealed material is used for preparing the nanowire composite lithium iron phosphate positive electrode material, so that the material has excellent conductivity, and the reversible capacity, the multiplying power performance and the cycle life of the battery are improved. Guoxiu Wang et al, university of WULONG, canada, published in Journal of PowerSources in 2008, prepared one-dimensional lithium iron phosphate nanowires without carbon coating by a hydrothermal method, and the specific capacity of the one-dimensional lithium iron phosphate nanowires is up to 140mAh/g, which shows that the shape control of the lithium iron phosphate has positive influence on improving the performance of the battery; then, researchers succeed in synthesizing various nano structures such as lithium iron phosphate nano rods, nano sheets, nano discs and the like. The prepared lithium iron phosphate was doped by researchers in an attempt to improve its physicochemical properties, such as Changhuan Zhang et al, university of east China, entitled "Effect of thermal treatment on the properties of electrospun LiFePO 4 Carbon nanofiber composite cathode materials for lithium-ion batteries article, a mixed solution of a lithium iron phosphate precursor and polyacrylonitrile is used as a reaction solution, nanowires are prepared in an electrostatic spinning mode, and then two sections of heating and carbonization are carried out to obtain a lithium iron phosphate/C composite material, the material has good electrical properties, the initial discharge capacity of the material at 0.5 ℃ is 146.3 mAh/g, and the material still has good stability after 100 circles, so that the electrical properties of the doped lithium iron phosphate can be properly improved. The traditional solid-phase method or liquid-phase method for preparing lithium iron phosphate is characterized in that the performance of the product is improved to a certain extent by a nanowire compounding technology or doping means, the cost is too high due to multiple sintering, and the whole preparation process is complex and tedious.
At present, the lithium iron phosphate cathode material synthesis technology has a plurality of technological routes, and the industrial technological routes of the lithium iron oxide red route, the ferrous oxalate route, the hydrothermal synthesis route and the orthophosphoric acid railway route are obtained. The lithium iron phosphate prepared by the orthophosphoric acid railway line has the advantages of good electrical property, low impurity content, relatively simple process steps and the like, and gradually becomes a unified technical trend of the industry. However, the iron phosphate prepared in the prior art has the problems of fluctuation in purity, undefined crystal structure and the like, and the obtained product lithium iron phosphate has the defects of poor processing effect due to low compaction density, low tap density and higher specific surface area, so that the electrochemical performance is lower, and in order to overcome the defect of lithium iron phosphate, the preparation process of the original auxiliary material is changed, the preparation process of the iron phosphate is improved, and the technical condition is optimized, so that the lithium iron phosphate material with excellent performance is prepared.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a method for preparing lithium iron phosphate (LEP) by using lithium iron phosphate (III), wherein the preparation method can prepare the lithium iron phosphate positive electrode material by sintering once, and the prepared lithium iron phosphate positive electrode material has the advantages of simple process, short flow, low cost, high compaction density, good crystallinity and excellent electrical property.
The technical scheme of the invention is as follows:
a method for preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate, comprising the steps of:
A. and (3) batching: according to Li 3 Fe 2 (PO 4 ) 3 And the mole ratio of iron in the iron source is (1.01-1.05) 1, raw materials are added, meanwhile, carbon sources accounting for 8-15% of the total amount of lithium iron (III) phosphate and the iron source in percentage by mass are added, and then doped metal oxide is added, wherein the mass percentage of the doped metal oxide accounts for 0.03-0.30% of the total amount of lithium iron (III) phosphate and the iron source in percentage by mass, so as to form ingredients;
B. ball milling: and (C) 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 for removing the magnetic substances.
C. Sintering: sintering the material except the magnetic substance obtained in the step B under the protection of inert gas after being dried, wherein the sintering system is divided into a lithium iron phosphate conversion temperature of 430-470 ℃, a correction temperature of 720-780 ℃ and a solidification temperature of 640-680 ℃, and then cooling to below 95 ℃ and discharging to obtain a lithium iron phosphate product;
as a further improvement of the present invention, the carbon source in the step a includes one or more of starch, glucose, sucrose, citric acid, polyethylene glycol, etc.; 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 the step a includes ferrous oxide, ferric hydroxide, ferrous hydroxide, ferric carbonate, ferric oxalate, ferric acetate, and the like, in addition to ferric oxide.
The doping materials are added in the form of oxides, hydroxides, carbonates or organic salts, so that anions such as sulfate radical, chloride ion and the like 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 to pollute the environment, and the production cost is increased.
As a further improvement of the invention, ball milling in the step B is divided into coarse milling and fine milling, permanent magnet iron removal is respectively carried out on the coarse milling and the fine milling, the materials contain 0.35-0.45ppm of magnetic substances, and the particle size D50=0.3-0.5 μm of the materials after fine milling.
As a further improvement of the present invention, the sintering schedule in the step C is: firstly, uniformly heating from room temperature to 200 ℃, wherein the heating time is 2 hours, and then uniformly heating from 200 ℃ to the conversion temperature, wherein the heating time is 4-6 hours; then the temperature is increased to 550 ℃ from the conversion temperature at a constant speed, the heating time is 3 hours, and then the temperature is increased to the correction temperature from 550 ℃ at a constant speed, and the heating time is 5-7 hours; and then cooling from the correction temperature to the solidification temperature at a constant speed for 5-6h, cooling to below 95 ℃ and discharging, and carrying out conventional crushing and packaging to obtain the lithium iron phosphate product.
As a further improvement of the invention, in the step C, when the temperature is raised to 430-470 ℃, the temperature is kept for 5-8 hours; when the temperature is raised to the correction temperature of 720-780 ℃, the temperature is kept for 8-12h, and when the temperature is lowered to the curing temperature of 640-680 ℃, the temperature is kept for 5-7h; the cooling time is 15-20h.
As a further optimization of the invention, in the conversion temperature stage, the temperature is firstly increased to 450-470 ℃ and kept for 4-5 hours, and then is reduced to 430 ℃ and kept for 1-2 hours; and then the temperature is raised to the correction temperature.
By Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 Mechanism analysis of lithium iron phosphate (LFP) prepared from+ carbon source as raw material is shown in FIG. 1-Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 As shown in the analysis chart of the synthetic thermogravimetry of the post-sintering of +carbon source, it can be derived from fig. 1: exothermic peaks formed by lithium iron phosphate crystal forms, i.e. Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 The temperature of conversion to lithium iron phosphate (LFP) is 430-470 ℃, the reaction is exothermic; the thermal weight curve (representing the weight change of the materials) shows that the lithium iron phosphate is perfect after 600 DEG, the experimental study shows that the correction temperature for perfect crystallization of the lithium iron phosphate is 720-780 ℃, the perfect lithium iron phosphate is solidified by 640-680 ℃, the obtained lithium iron phosphate has perfect crystal lattice, carbon is uniformly distributed among particles and forms compact carbon coating, the compaction density of the product can reach 2.6g/mL and is far higher than the conventional compaction density of 2.3 g/mL, and the BET of the product is controllable and is generally less than 18m 2 And/g, the processability of the product is better.
In the sintering system in the step C, the inert gas comprises the following components: gases such as nitrogen, helium, neon, etc.; controlling the oxygen concentration to be 10-100ppm and the micro positive pressure in the furnace to be 10-100Pa; and (5) conventionally crushing and packaging the discharged materials to obtain a lithium iron phosphate product.
In the ball milling process, the dispersing agent sodium dodecyl benzene sulfonate is adopted to fully mix the lithium iron (III) phosphate, the ferric oxide and the carbon source, so that the agglomeration of the ferric oxide which is easy to produce colloid 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; the magnetic iron removal is carried out in the ball milling stage, at the moment, the granularity of the material is finer, the wrapping around the magnetic substance is removed as much as possible, the removal of the magnetic substance is more thorough, the content of the magnetic substance is close to half of that 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 adopted to carry out spherical granulation, so that the tap density and the compaction density are increased, and the energy density per unit volume is higher; the sintering system process comprises the steps of conversion temperature, correction temperature and curing temperature, the ferric iron phosphate has complete crystal lattice, the carbon coating is more perfect, the migration rate of Li ions 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, and certainly comprise the defective lithium iron phosphate (LFP) raw materials which can generate the lithium iron (III) phosphate and the ferric oxide by a certain technical means, and also comprise the purer lithium iron phosphate anode materials which are disassembled from the lithium iron phosphate battery and separated. Therefore, the method has the advantages of wide raw materials and environment-friendly circular economy along with the arrival of the expense report period of a large number of lithium iron phosphate batteries.
2. The invention removes the iron through the magnetism of the ball milling stage, the magnetic substance is removed more thoroughly, and meanwhile, the iron removing procedure is reduced; the spray granulation and sintering processes carry out tight carbon coating on the lithium iron phosphate through three stages of conversion temperature, correction temperature and solidification temperature, carbon is uniformly distributed among particles, meanwhile, the defect of the lithium iron phosphate is prevented, the purity of the product lithium iron phosphate is ensured, and the lithium iron phosphate material with high conductivity and low internal resistance can be obtained through the technology, 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 cycle can reach 3000 circles, and the performance is equivalent to that of middle-high-end lithium iron phosphate on the market. Can be well applied in the energy storage industry and the power battery industry.
3. The invention is especially applied to the raw materials of waste lithium iron phosphate anode materials, has the advantages of reasonable process, low manufacturing cost, environmental protection, no toxicity and the like, and has the electrochemical performance meeting the requirements of olivine lithium iron phosphate battery materials sold in the market, and the application prospect is very wide.
Drawings
FIG. 1Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 Synthetic thermogravimetric analysis of sintering after +carbon source
FIG. 2 is Li 3 Fe 2 (PO 4 ) 3 With Fe 2 O 3 XRD pattern after ball milling and drying
FIG. 3 is a 0.2C charge/discharge curve of the lithium iron phosphate cathode material prepared in example 1
FIG. 4 is a graph showing the cycle of 1C of the lithium iron phosphate cathode material prepared in example 1
FIG. 5 is a graph showing the cycle performance of the lithium iron phosphate cathode material after the repair of example 4
FIG. 6 is a graph showing the rate performance of the lithium iron phosphate cathode material after repair of example 5
Fig. 7 is a process flow diagram of the present invention.
Detailed Description
In order to make the technical problems, technical schemes and beneficial effects solved by the invention more clear, the invention is further described in detail below with reference to the embodiments. It should be understood that the specific examples described herein are for the purpose of illustrating the present invention only and are not intended to limit the present invention, and the present invention includes other embodiments and modifications thereof within the scope of the technical ideas thereof.
In the present invention, li is sometimes increased depending on the material 3 Fe 2 (PO 4 ) 3 The preparation steps of the method are reduced, or the steps of magnetic iron removal and the like are reduced, or the screening step of lithium iron phosphate is added, but the method can be applied as long as the basic process flow is unchanged.
An embodiment of the present invention provides a method for preparing lithium iron phosphate (LEP) using lithium iron phosphate (iii), see fig. 6. The invention is further illustrated by the following specific examples.
Example 1
Step A, batching according to Li 3 Fe 2 (PO 4 ) 3 With Fe 2 O 3 The molar ratio of the middle iron is 1.01:1, li 3 Fe 2 (PO 4 ) 3 With Fe 2 O 3 Preparing raw materials, and simultaneously, the mass percentage of the raw materials is Li 3 Fe 2 (PO 4 ) 3 With Fe 2 O 3 15% of the total mass of the mixture is added with starch and alumina, the mass percentage of the alumina is Li 3 Fe 2 (PO 4 ) 3 With Fe 2 O 3 0.30% of the total mass of (b).
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 of anionic dispersant sodium dodecyl benzene sulfonate, removing iron by using a permanent magnet in the process, and the magnetic substance content in the materials after ball milling is 0.35ppm and the particle size D50=0.3 mu m.
Step C, sintering, namely sintering the material except the magnetic substance obtained in the step B under the protection of nitrogen after the material is dried, heating at a constant speed in each heating stage, wherein the time from the room temperature to 200 ℃ is 2 hours, the time from the room temperature to the conversion temperature is 4 hours, the conversion temperature is 470 ℃, and the constant temperature is 5 hours; then the time to 550 ℃ is 3 hours, the time to the correction temperature is 5 hours, the correction temperature is 720 ℃, the constant temperature is 12 hours, the time from the cooling to the solidifying temperature after the correction temperature is 5 hours, the solidifying temperature is 680 ℃, the constant temperature is 5 hours, the cooling 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 100Pa.
And C, crushing and packaging the discharged materials in the step, wherein the obtained lithium iron phosphate has the following indexes:
from the index of lithium iron phosphate and the 1C circulation chart of FIG. 4, the compaction density is higher than that of LFP product 2.3 g/mL in the conventional market, the initial efficiency of 0.1C is far more than 95%, the initial discharge of 1C is up to 151 mAh/g, the circulation efficiency of 2000 times is up to 92.3%, the required efficiency of the conventional manufacturer is far more than 85%, and the magnetic substance is half of the required efficiency of the conventional manufacturer.
Example 2
Step A, proportioning according to the following weight ratioLi 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 (C 2 O 4 ) 3 · 5H 2 The raw materials are mixed in a molar ratio of O=1.05:1, meanwhile polyethylene glycol accounting for 8% of the total mixing amount by mass percent is mixed in, and alumina accounting for 0.03% by mass 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 3.8:1, adding 0.08g/L of anionic dispersant sodium dodecyl benzene sulfonate, removing iron by using a permanent magnet in the process, and the magnetic substance content in the materials after ball milling is 0.45ppm and the particle size D50=0.5 mu m.
Step C, sintering, namely sintering the material except the magnetic substance obtained in the step B under the protection of helium after the material is dried, heating at a constant speed in each heating stage, wherein 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 is 8 hours; then the time to 550 ℃ is 3 hours, the time to the correction temperature is 7 hours, the correction temperature is 780 ℃, the constant temperature is 8 hours, the time from the cooling to the solidifying temperature after the correction temperature is 6 hours, the solidifying temperature is 640 ℃, the constant temperature is 7 hours, the cooling period is 15 hours, and the furnace is taken out from the furnace 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 10Pa.
And C, crushing and packaging the discharged materials in the step, wherein the obtained lithium iron phosphate has the following indexes:
the compaction density is higher than 2.3 g/mL of LFP product in the conventional market, the initial efficiency of 0.1C is far more than 95%, the initial discharge of 1C reaches 153 mAh/g, the cycle efficiency of 2000 times reaches 91.5%, the compaction density is far more than 85% required by common factories, and the magnetic substance is half of that required by the conventional factories.
Example 3
Step A, batching according to Li 3 Fe 2 (PO 4 ) 3 And FeO molar ratio = 1.03:2, while adding grape at 11% mass percent of total ingredientsSugar and 0.20% by mass of magnesium oxide were 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, permanent magnets are used for iron removal during ball milling, the magnetic substance content in the materials after ball milling is 0.40ppm, and the particle size D50=0.4 mu m.
Step C, sintering, namely sintering the material except the magnetic substance obtained in the step B under the protection of neon after the material is dried, heating at a constant speed in each heating stage, 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; then the time from the corrected temperature to the solidified temperature is 3 hours, the time from the corrected temperature to the solidified temperature is 6 hours, the corrected temperature is 750 ℃, the constant temperature is 10 hours, the time from the corrected temperature to the solidified temperature is 5.5 hours, the solidified temperature is 660 ℃, the constant temperature is 6 hours, the cooling period is 18 hours, and the furnace is taken out from the furnace at 85 ℃; the oxygen concentration is controlled to be 50ppm in the whole sintering process, and the micro positive pressure in the furnace is 30Pa.
And C, crushing and packaging the discharged materials in the step, wherein the obtained lithium iron phosphate has the following indexes:
the compaction density is higher than 2.3 g/mL of LFP product in the conventional market, the initial efficiency of 0.1C is far more than 95%, the initial discharge of 1C reaches 154 mAh/g, the cycle efficiency of 2000 times reaches 92.0%, the compaction density is far more than 85% required by the conventional manufacturer, and the magnetic substance is half of that required by the conventional manufacturer.
Example 4
Step A, roasting, namely detecting components of lithium iron phosphate secondary powder generated in the purchased production process, wherein P is Fe, li=1:1.02:1.04 (molar ratio), and the balance of impurities: micro amount of Al, mg, ca and the like, roasting the detected lithium iron phosphate secondary powder to obtain Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 And (3) a mixture.
And B, proportioning, namely adding 12 mass percent of sucrose into the mixture obtained in the step A according to the total proportioning amount, and weighing magnesium oxide with the mass percent of 0.15 percent.
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, permanent magnets are used for iron removal during ball milling, the magnetic substance content in the materials after ball milling is 0.41ppm, and the particle size D50=0.35 mu m.
Step D, sintering, namely sintering the material except the magnetic substance obtained in the step C under the protection of nitrogen after the material is dried, heating at a constant speed in each heating stage, wherein the time from 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 is 6 hours; then the temperature is 3h to 550 ℃, the time is 5.5h to the correction temperature, the temperature is 740 ℃, the constant temperature is 9h, the time from the cooling to the solidifying temperature after the correction temperature is 5.2h, the solidifying temperature is 670 ℃, the constant temperature is 5.5h, the cooling period is 16h, and the furnace is taken out from the furnace at 92 ℃; the oxygen concentration is controlled to be 80ppm in the whole sintering process, and the micro positive pressure in the furnace is 40Pa.
And C, crushing and packaging the discharged materials in the step, wherein the obtained lithium iron phosphate has the following indexes:
according to the index of the lithium iron phosphate and the 1C circulation chart of FIG. 5, the compaction density is higher than that of the LFP product in the conventional market by 2.3 g/mL, the initial efficiency of 0.1C is far more than 95%, the initial discharge of 1C is up to 151 mAh/g, the circulation efficiency of 2000 times is up to 92.1%, the required efficiency is far more than 85% of the common manufacturer, and the magnetic substance is half of the required efficiency of the conventional manufacturer; the product is superior to the patent 2018108877359 in terms of processing performance evaluation and electrochemical capacity evaluation, and the electrochemical capacity of the product with the performance 1C of the patent 2018108877359 is about 145 mAh/g.
Example 5
Step A, roasting, namely detecting components of lithium iron phosphate waste powder which is disassembled from waste lithium iron phosphate batteries delivered from different factories and has different defects and different granularity, wherein P is as follows, fe is as follows, li=1:0.96:0.75 (molar ratio), and the rest impurities are as follows: a is thatThe content of l and F are respectively 0.41 percent and 0.28 percent, iron carbonate and lithium carbonate are added into the detected lithium iron phosphate waste powder according to the molar ratio of P to Fe to Li=1 to 1 to 1.03, and the mixture is ball-milled and mixed and then baked to obtain Li 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 And (3) a mixture.
And B, compounding, namely adding 12% of the total compounding amount of the mixture obtained in the step A into sucrose according to the mass percentage.
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, permanent magnets are used for iron removal during ball milling, the magnetic substance content in the materials after ball milling is 0.39ppm, and the particle size D50=0.36 mu m.
Step D, sintering, namely sintering the material except the magnetic substance obtained in the step C under the protection of nitrogen after the material is dried, heating at a constant speed in each heating stage, wherein the time from the room temperature to 200 ℃ is 2 hours, the time from the room temperature to the conversion temperature is 4.8 hours, the conversion temperature is 460 ℃, and the constant temperature is 5.8 hours; then the temperature is 3h to 550 ℃, then the temperature is corrected to 6.2h, the temperature is corrected to 762 ℃, the constant temperature is kept for 11h, the time from the corrected temperature to the solidifying temperature is 5.2h, the solidifying temperature is 666 ℃, the constant temperature is kept for 6.3h, the cooling period is 17.8h, and the furnace is discharged below 94 ℃; the oxygen concentration is controlled to be 60ppm in the whole sintering process, and the micro positive pressure in the furnace is 70Pa.
And D, crushing and packaging the furnace discharging material in the step, wherein the obtained lithium iron phosphate has the following indexes:
according to the lithium iron phosphate index and the multiplying power performance curve chart of the product, the compaction density is higher than 2.3 g/mL of the LFP product on the conventional market, the initial efficiency of 0.1C is far more than 95%, the initial discharge of 1C is 146mAh/g, the cycle efficiency of 2000 times is 90.7%, the requirement of a common manufacturer is far more than 85%, and the magnetic substance is half of the requirement of the conventional manufacturer; the product is superior to the patent 2018108877359 in terms of processing performance evaluation and electrochemical capacity evaluation of the product, particularly when a certain amount of Cu and F impurities are contained in lithium iron phosphate waste, the product performance, particularly the electrochemical capacity of 1C, produced by the patent 2018108877359 is lower than 135 mAh/g, so that the product performance produced by the method is superior, and the raw material adaptability is wider; meanwhile, the F content in the product is obviously lower than that 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 repair of the lithium iron phosphate waste powder which is difficult to solve by other methods.
In the embodiment, the impurity Al and F content separated from the waste lithium iron phosphate battery are respectively 0.41 percent and 0.28 percent of lithium iron phosphate waste powder, and Li is obtained after pretreatment 3 Fe 2 (PO 4 ) 3 And Fe (Fe) 2 O 3 The multiplying power performance curve of the mixture and the prepared lithium iron phosphate positive electrode material is shown in fig. 6, and the multiplying power performance of the mixture can be obtained from fig. 5: 0.2-150.7 mAh/g, 0.5-148.3 mAh/g, 1-144.3 mAh/g, 2-137.3 mAh/g, 5-123.7 mAh/g. Meanwhile, the invention has strong adaptability and can be popularized and applied.
The foregoing description of the preferred embodiments of the invention is not intended to limit the invention to the particular embodiments disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Claims (3)
1. A method for preparing lithium iron phosphate (LEP) using lithium iron phosphate (iii), comprising the steps of:
A. and (3) batching: according to Li 3 Fe 2 (PO 4 ) 3 And the mole ratio of iron in the iron source is (1.01-1.05) 1, raw materials are added, meanwhile, carbon sources accounting for 8-15% of the total amount of lithium iron (III) phosphate and the iron source in percentage by mass are added, and then doped metal oxide is added, wherein the mass percentage of the doped metal oxide accounts for 0.03-0.30% of the total amount of lithium iron (III) phosphate and the iron source in percentage by mass, so as to form ingredients; wherein the iron source is one or more of ferric oxide, ferrous oxide, ferric hydroxide, ferrous hydroxide, ferric carbonate, ferric oxalate and ferric acetate;
B. ball milling: adding the ingredients obtained in the step A into a ball mill for ball milling, wherein the ball milling is divided into coarse milling and fine milling, the coarse milling and the fine milling respectively remove magnetic substances by using permanent magnets, the magnetic substances in the materials are controlled to be 0.35-0.45ppm, and the particle size D50 of the materials after the fine milling is 0.3-0.5 mu m; the liquid-solid ratio during ball milling is (2.2-3.8): 1, and the material for removing the magnetic substance is obtained;
C. sintering: sintering the material except the magnetic substance obtained in the step B under the protection of inert gas after the material is dried, wherein the sintering system is to heat up at a constant speed in sections according to the temperature change of each stage, the time from room temperature to 200 ℃ is 2 hours, and the time from room temperature to the conversion temperature is 4-6 hours; the time from the conversion temperature to 550 ℃ is 3 hours, and the time from the conversion temperature to the correction temperature is 5-7 hours; cooling from the corrected temperature to the solidification temperature for 5-6h; the sintering system is divided into a lithium iron phosphate conversion temperature of 430-470 ℃, a correction temperature of 720-780 ℃ and a curing temperature of 640-680 ℃; in the conversion temperature stage, firstly, heating to 450-470 ℃ for 4-5h, then cooling to 430 ℃ for 1-2h, and then heating to the correction temperature; the conversion temperature, the correction temperature and the solidification temperature are respectively kept for 5-8h, 8-12h and 5-7h, then the cooling period is 15-20h, and the lithium iron phosphate is obtained after the lithium iron phosphate is cooled to below 95 ℃.
2. A method of preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, characterized by: 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 of preparing lithium iron phosphate (LEP) using lithium iron (iii) phosphate according to claim 1, characterized by: in the sintering system in the step C, the inert gas is one of helium and neon; controlling oxygen concentration to be 10-100ppm during sintering, and micro-positive pressure in the furnace to be 10-100Pa; and (5) conventionally crushing and packaging the discharged materials to obtain a lithium iron phosphate product.
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| CN102208706A (en) * | 2011-05-04 | 2011-10-05 | 合肥国轩高科动力能源有限公司 | Recycling treatment method of waste and old lithium iron phosphate battery anode materials |
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