CN110436431B - Preparation method of lithium iron phosphate cathode material and lithium ion battery - Google Patents
Preparation method of lithium iron phosphate cathode material and lithium ion battery Download PDFInfo
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Abstract
The invention provides a preparation method of a lithium iron phosphate anode material, which comprises the following steps: (1) adding a first lithium source, a phosphorus source, an iron source and a first carbon source into a first solvent containing a complexing agent to obtain a mixed solution, uniformly stirring at the temperature of 400-450 ℃, and drying and crushing to obtain a precursor I; (2) uniformly mixing iron phosphate particles and a second lithium source according to a molar ratio of 1 (1.03-1.1), then adding a second carbon source, a second solvent and doped metal salt, fully mixing, grinding for 3-8 hours, drying and crushing to obtain a precursor II; (3) uniformly mixing the precursor I and the precursor II according to the mass ratio of 1 (0.5-3) to obtain a mixed precursor; then sintering at high temperature in an inert or reducing atmosphere to obtain a lithium iron phosphate crude product; (4) and crushing and drying the crude lithium iron phosphate product in an air flow mill, and then collecting to obtain the lithium iron phosphate anode material. The invention also provides a lithium ion battery.
Description
Technical Field
The invention relates to the field of lithium ion batteries, in particular to a preparation method of a lithium iron phosphate anode material and a lithium ion battery.
Background
Lithium ion batteries are internationally recognized as ideal energy storage and output power sources due to their high volumetric energy density, mass energy density and excellent cycle performance, and increasingly show their important roles in various fields. The quality of energy density is one of important indexes for measuring the lithium ion battery, the compaction density influences the energy density of the battery to a great extent, theoretically, the energy density of the battery is in direct proportion to the compaction density, and the larger the compaction density is, the higher the battery capacity is. At present, lithium iron phosphate on the market is generally low in compaction density, and is generally 2.2-2.3g/cm3To (c) to (d); in addition, multiple sintering exists in the preparation process of the traditional solid-phase method or liquid method of lithium iron phosphate, so that the cost is too high, and the whole preparation process is complex and tedious.
Disclosure of Invention
In view of the above, the present invention provides a preparation method of a lithium iron phosphate positive electrode material and a lithium ion battery, the preparation method of the lithium iron phosphate positive electrode material can prepare the lithium iron phosphate positive electrode material only by one-time sintering, the process method is simple, the cost is low, and the prepared lithium iron phosphate positive electrode material has high compacted density, good crystallinity and large energy density per unit volume.
Specifically, in a first aspect, the invention provides a preparation method of a lithium iron phosphate positive electrode material, which comprises the following steps:
(1) adding a first lithium source, a phosphorus source, an iron source and a first carbon source into a first solvent containing a complexing agent to obtain a mixed solution, uniformly stirring at the temperature of 400-450 ℃, and drying and crushing to obtain a precursor I;
(2) uniformly mixing iron phosphate particles and a second lithium source according to a molar ratio of 1 (1.03-1.1), then adding a second carbon source, a second solvent and doped metal salt, fully mixing, grinding for 3-8 hours, and drying and crushing to obtain a precursor II, wherein the mass percentage content of the second carbon source is 2.9-8.7%;
(3) placing the precursor I and the precursor II in a mixer according to the mass ratio of 1 (0.5-3) and uniformly mixing to obtain a mixed precursor; then sintering at high temperature in an inert or reducing atmosphere to obtain a lithium iron phosphate crude product;
(4) and (3) crushing and drying the crude lithium iron phosphate product in an air flow mill by using the heated high-temperature compressed air as a crushing and drying air source, and then collecting to obtain the lithium iron phosphate anode material.
Optionally, in the step (1), the first lithium source includes one or more of lithium phosphate, lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate, and lithium oxalate. For example, in one embodiment of the present invention, the first lithium source may be lithium phosphate or lithium carbonate. In another embodiment of the present invention, the first lithium source may be lithium carbonate and lithium hydroxide.
Optionally, the source of phosphorus comprises one or more of phosphoric acid, diammonium phosphate, and monoammonium phosphate.
The iron source may include one or more of ferric oxide, ferric phosphate, ferrous citrate, ferrous oxalate, and ferrous sulfate.
Optionally, the first carbon source comprises one or more of carbon nanotubes, graphite, phenolic resin, sucrose, glucose, ascorbic acid, and starch.
Optionally, the first solvent comprises at least one of deionized water, methanol, ethanol, acetone, and isopropyl alcohol.
Further, the first carbon source may include at least two of carbon nanotubes, graphite, phenolic resin, sucrose, glucose, ascorbic acid, and starch. For example, in one embodiment of the present invention, the carbon source is glucose and ascorbic acid. Or in another embodiment of the present invention, the carbon source is glucose, carbon nanotubes and phenolic resin.
Optionally, in step (1), the molar ratio of the first lithium source, the phosphorus source, and the iron source is (1-3) to 1: 1; the mass percentage of the first carbon source is 5-10%.
For example, the first carbon source accounts for 5% by mass, or 8% by mass, or 10% by mass of the precursor (r).
Optionally, the complexing agent is citric acid; the molar ratio of the complexing agent to the iron source is (0.5-3): 1.
Optionally, in the step (1), the stirring time of the stirring process is 120-145 min. The stirring process is a constant-temperature stirring process.
Optionally, in the step (1), the pH of the mixed solution is 7.0 to 9.0. In the step (1), under the pH condition of 7.0-9.0 and the temperature of 400-450 ℃, all raw materials in the mixed solution react to form nano-scale precipitates, and the precursor (i) with the nano-scale particle size is obtained after drying and crushing treatment.
Optionally, the particle size of the precursor (i) is 0.1-0.6 μm.
Further, optionally, the particle size of the precursor (i) is 0.4-0.6 μm
Optionally, in the step (2), the second lithium source includes one or more of lithium phosphate, lithium carbonate, lithium nitrate, lithium hydroxide, lithium acetate, and lithium oxalate. In the present invention, the first lithium source and the second lithium source may be the same or different.
Optionally, the doped metal salt comprises magnesium sulfate (MgSO)4) Aluminum sulfate (Al)2(SO4)3) Titanium nitrate (Ti (NO)3)4) And niobium pentoxide (Nb)2O5) One or more of (a). For example, in one embodiment of the present invention, the doped metal salt is Nb2O5Or Ti (NO)3)4And the like.
Further, optionally, the doped metal salt includes at least two of magnesium sulfate, aluminum sulfate, titanium nitrate, and niobium pentoxide. For example, in one embodiment of the present invention, the doped metal salt is titanium nitrate and niobium pentoxide. In another embodiment of the present invention, the doped metal salt is aluminum sulfate, titanium nitrate and niobium pentoxide.
Optionally, in the precursor (II), the mass percentage of the doped metal salt is 0.12-0.41%.
Optionally, the second carbon source comprises one or more of carbon nanotubes, graphite, phenolic resin, sucrose, glucose, ascorbic acid, and starch. In the present invention, the first carbon source and the second carbon source may be the same or different.
Optionally, the second solvent comprises at least one of deionized water, methanol, ethanol, acetone, and isopropyl alcohol. In the present invention, the second solvent is different from the first solvent. For example, when the first solvent is methanol and/or deionized water, the second solvent may be ethanol, or acetone.
Optionally, in step (2), the particle size of the iron phosphate particles is 1.1-2.5 μm.
In the process of the step (2), through the full grinding process of each raw material in the second solvent, the raw materials comprising iron phosphate particles, a second lithium source, a second carbon source, doped metal salt and the like can be promoted to be fully mixed; wherein, the doping elements in the doped metal salt can be dispersed more uniformly; then drying and crushing to obtain the precursor II with uniform particle size and uniformly distributed components.
Optionally, the particle size of the precursor (c) is 1.1-2.5 μm.
Further, optionally, the particle size of the precursor (C) is 1.5-2.5 μm. The particle size of the precursor (II) is larger than that of the precursor (I).
For example, the particle size of the precursor (i) may be 0.1 μm, or 0.3 μm, or 0.5 μm, or 0.6 μm, or 0.8 μm. The particle size of the precursor (II) can be 1.1 mu m, or 1.5 mu m, or 1.8 mu m, or 2.0 mu m, or 2.5 mu m.
In the invention, precursors (I) and precursors (II) with different particle sizes are mixed; the characteristic that the particle size of the precursor I is small is utilized, the precursor I can be effectively embedded into gaps among particles, and the precursor II and the particles are fully mixed; after further high-temperature sintering and jet milling, the energy density of the product in unit volume can be greatly improved, so that the compacted density of the product is higher, and a lithium iron phosphate anode material product is obtained. And meanwhile, in the mixing and sintering process of the precursor I with smaller particle size, the doping elements can be further and better uniformly dispersed, and finally the lithium iron phosphate anode material with more uniform distribution, better performance and higher compaction density of the doping elements is obtained.
In the invention, a nanometer-scale precursor can be formed due to the reaction in the step (1); when the doped metal salt is added in the step (1), carbon and the doped element can coat the surface of the precursor, and the growth direction of crystals can be limited in the subsequent sintering process, so that the electrical property of the lithium iron phosphate anode material is poorer than that of the product prepared by the method of adding the doped metal salt in the step (2).
Further, optionally, the mass ratio of the precursor (i) to the precursor (ii) is 1 (0.5-1.5).
Further, optionally, the mass ratio of the precursor (i) to the precursor (ii) is 1 (2-3).
In the invention, the precursor I and the precursor II in the mass ratio range can realize more compact embedding, which is beneficial to improving the distribution uniformity of doped metal salt and the compaction density of a lithium iron phosphate anode material product.
Optionally, in the step (3), the inert or reducing atmosphere may include, but is not limited to, an atmosphere of nitrogen, argon, or carbon monoxide.
Optionally, in the high-temperature sintering process, sintering is performed in a temperature rise mode of 20-40 ℃/h, the sintering temperature is 200-900 ℃, and the sintering time is 10-25 hours.
Optionally, in the step (4), in the air flow milling process, the air flow temperature is 160-.
In the invention, the D97 particle size of the lithium iron phosphate anode material is 4-8 μm; the compacted density of the lithium iron phosphate anode material is 2.43-2.52g/cm3。
In the invention, the molar percentage content of the doped metal element in the lithium iron phosphate anode material is 0.04-0.82%. The molar percentage of the doped metal element may be 0.04%, or 0.14%, or 0.28%, or 0.41%, or 0.64%, or 0.82%. The doped metal elements in the molar percentage content range can further improve the electrical property of the lithium iron phosphate anode material, improve the migration rate of Li ions and reduce the concentration polarization of the Li ions in the charging and discharging process.
In a second aspect, the invention further provides a lithium ion battery, which includes the lithium iron phosphate positive electrode material prepared by the preparation method in the first aspect of the invention.
Further, the lithium ion battery comprises a positive electrode, a negative electrode, a diaphragm and electrolyte, wherein the positive electrode comprises the lithium iron phosphate positive electrode material prepared by the preparation method of the first aspect.
In the lithium ion battery provided by the second aspect of the invention, the lithium ion migration rate in the lithium ion battery is high, the concentration polarization phenomenon of the lithium ions in the charging and discharging process is weak, and the lithium ion battery has high rate capability. Besides the application in lithium ion batteries, the lithium iron phosphate cathode material can also be used as the cathode material of other types of batteries.
In conclusion, the beneficial effects of the invention include the following aspects:
(1) the preparation method of the lithium iron phosphate anode material provided by the invention has the advantages that the process production flow is simplified, the lithium iron phosphate anode material can be prepared only by one-time sintering, the energy consumption is low, the cost is low, the large-scale industrial production can be realized, and the lithium iron phosphate anode material with high efficiency and stable product quality can be obtained.
(2) The preparation method of the lithium iron phosphate cathode material provided by the invention respectively prepares a precursor (i) with smaller particle size and a precursor (ii) with larger particle size and containing doping elements, and the precursor are well combined in an embedded and large-particle and small-particle mixing mode to obtain a lithium iron phosphate finished product with larger energy density, higher compaction density and more stable performance in unit volume.
(3) The lithium iron phosphate anode material prepared by the preparation method provided by the invention has the advantages that the doped metal elements are uniformly distributed, and the compaction density is higher; the lithium ion battery prepared by the lithium iron phosphate anode material has the advantages that the migration rate of Li ions is rapidly improved, the concentration polarization of the Li ions in the charging and discharging process is effectively reduced, and the high-rate discharging coulomb efficiency is obviously improved.
Drawings
Fig. 1 is a flowchart illustrating a preparation process of a lithium iron phosphate positive electrode material according to an embodiment of the present invention;
fig. 2 is a scanning electron microscope image of the lithium iron phosphate positive electrode material in embodiment 1 of the present invention;
fig. 3 is another scanning electron microscope image of the lithium iron phosphate positive electrode material in embodiment 1 of the present invention;
fig. 4 is an XRD spectrum of the lithium iron phosphate positive electrode material in example 1 of the present invention.
Detailed Description
While the following is a description of the preferred embodiments of the present invention, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention.
As shown in fig. 1, in an embodiment of the present invention, a preparation method of a lithium iron phosphate positive electrode material is provided, which includes the following steps:
s01, adding a first lithium source, a phosphorus source, an iron source and a first carbon source into a first solvent containing a complexing agent to obtain a mixed solution, uniformly stirring at the temperature of 400-450 ℃, and drying and crushing to obtain a precursor I;
s02, uniformly mixing iron phosphate particles and a second lithium source according to a molar ratio of 1 (1.03-1.1), adding a second carbon source, a second solvent and doped metal salt, fully mixing, grinding for 3-8 hours, and drying and crushing to obtain a precursor, wherein the mass percentage content of the second carbon source is 2.9-8.7%;
s03, placing the precursor I and the precursor II in a mixer according to the mass ratio of 1 (0.5-3) and uniformly mixing to obtain a mixed precursor; then sintering at high temperature in an inert or reducing atmosphere to obtain a lithium iron phosphate crude product;
and S04, crushing and drying the lithium iron phosphate crude product in an air flow mill by using the heated high-temperature compressed air as a crushing and drying air source, and then collecting to obtain the lithium iron phosphate anode material.
The following examples are intended to illustrate the invention in more detail.
Example 1
A preparation method of a lithium iron phosphate positive electrode material comprises the following steps:
(1) adding lithium carbonate, ammonium dihydrogen phosphate and ferrous oxalate into a reaction kettle according to a molar ratio of 0.5:1:1, adding a proper amount of glucose and a proper amount of methanol, adjusting the pH to 7.0, heating and stirring at the temperature of 420 ℃ for 125min until the mixture is uniform, reacting to form a complex, drying at the temperature of 120 ℃ by using a dryer, and crushing by using a crusher until the particle size of powder is within the range of 0.1-D90-0.6 mu m to obtain a precursor I;
(2) iron phosphate particles and lithium carbonate are selected to be mixed and stirred uniformly according to the molar ratio of 1:1.036, and glucose with the mass percentage of 6.9%, methanol with the mass percentage of 4.3% and MgSO 0.26% are added4After fully mixing, grinding for 7.5h, drying at 120 ℃ by using a dryer, and crushing by using a crusher until the particle size is within the range of 1.1-2.5 mu m from D90 to obtain a precursor II;
(3) uniformly mixing the precursor I and the precursor II prepared in the steps (1) and (2) in a horizontal mixer according to the mass ratio of 1:1.195 to obtain a precursor mixture; then, high-temperature sintering is carried out in a nitrogen environment, the sintering temperature is 640 ℃, the temperature rising efficiency is controlled to be 40 ℃/h, the temperature rising mode is gradually increased, and the sintering time is 22.5 hours;
(4) and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97, and collecting the material to obtain the lithium iron phosphate anode material.
Fig. 2 and 3 are scanning electron micrographs of lithium iron phosphate cathode material finished products prepared in example 1; as can be seen from fig. 2 and 3, the particle size of the finished lithium iron phosphate cathode material is D97 of which the particle size is not less than 5.15 μm, the lithium iron phosphate cathode material has uniform morphology and size, and the crystal phases are arranged closely. It can be seen from the X-ray diffraction (XRD) characterization chart of the finished lithium iron phosphate cathode material, referring to fig. 4, that the position of the peak is substantially coincident with the peak of pure-phase lithium iron phosphate, and no impurity peak appears, the finished lithium iron phosphate cathode material prepared by the preparation method shows pure-phase lithium iron phosphate, and the lithium iron phosphate lattice is not destroyed by doping metal elements, so that the doping of metal elements is very successful.
Example 2
A preparation method of a lithium iron phosphate positive electrode material comprises the following steps:
(1) adding lithium hydroxide, phosphoric acid and ferrous sulfate into a reaction kettle according to the mol ratio of 3:1:1, then adding a proper amount of carbon nano tube and ethanol, adjusting the pH to 7.0, heating at the temperature of 420 ℃, simultaneously stirring for 125min till uniformity, reacting to form a complex, drying at the temperature of 120 ℃ by using a dryer, and crushing by using a crusher until the particle size of powder is within the range of 0.4-D90-0.6 mu m to obtain a precursor I;
(2) iron phosphate particles and lithium hydroxide are selected to be mixed and stirred uniformly according to the proportion of 1:1.036, and glucose with the mass percentage of 6.9 percent, methanol with the mass percentage of 4.3 percent and Ti (NO) with the mass percentage of 0.26 percent are added3)4After fully mixing, grinding for 7.5h, drying at 120 ℃ by using a dryer, and crushing by using a crusher until the particle size is within the range of 1.5 mu m to 2.5 mu m from D90 to obtain a precursor II;
(3) uniformly mixing the precursor I and the precursor II prepared in the steps (1) and (2) in a horizontal mixer according to the mass ratio of 1:1.195 to obtain a precursor mixture; then placing the mixture in a nitrogen condition for high-temperature sintering, wherein the reaction temperature is 640 ℃, the temperature-raising efficiency is controlled to be 40 ℃/h, the temperature-raising mode is gradually raised, and the sintering time is 22.5 hours;
(4) and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97, so as to obtain the lithium iron phosphate cathode material.
Example 3
A preparation method of a lithium iron phosphate positive electrode material comprises the following steps:
(1) adding lithium acetate and ferric phosphate into a reaction kettle according to a molar ratio of 3:1, adding a proper amount of sucrose and ethanol, adjusting the pH to 8.0, heating at 420 ℃ and stirring for 125min to be uniform, reacting to form a complex, drying at 120 ℃ by using a dryer, and crushing by using a crusher until the particle size of powder is within the range of 0.1-D90-0.5 mu m to obtain a precursor I;
(2) iron phosphate particles and lithium acetate are selected according to the molar ratio of 1:1.036 to be mixed and stirred uniformly, and then 6.9 mass percent of glucose, 4.3 mass percent of methanol and 0.26 mass percent of Al are added2(SO4)3After fully mixing, grinding for 7.5 hours, drying in a dryer, and crushing by a crusher until the particle size is within the range of 1.1 mu m to 2.0 mu m from D90 to obtain a precursor II;
(3) uniformly mixing the precursor I and the precursor II prepared in the steps (1) and (2) in a horizontal mixer according to the mass ratio of 1:1.195 to obtain a precursor mixture; then, high-temperature sintering is carried out under the condition of nitrogen, the reaction temperature is 640 ℃, the temperature rising efficiency is controlled to be 40 ℃/h, the temperature rising mode is gradually increased, and the sintering time is 22.5 hours;
(4) and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97, and collecting the material to obtain the lithium iron phosphate anode material.
Example 4
A preparation method of a lithium iron phosphate positive electrode material comprises the following steps:
(1) adding lithium acetate and ferric phosphate into a reaction kettle according to a molar ratio of 3:1, adding a proper amount of sucrose and ethanol, adjusting the pH to 8.0, heating at 420 ℃ and stirring for 125min to be uniform, reacting to form a complex, drying at 120 ℃ by using a dryer, and crushing by using a crusher until the particle size of powder is within the range of 0.1-D90-0.5 mu m to obtain a precursor I;
(2) iron phosphate particles and lithium acetate are selected according to the molar ratio of 1:1.036 to be mixed and stirred uniformly, and then glucose with the mass percentage of 6.9 percent, methanol with the mass percentage of 4.3 percent and Nb with the mass percentage of 0.15 percent are added2O5And 0.15% of Al2(SO4)3After fully mixing, grinding for 7.5 hours, drying in a dryer, and crushing by a crusher until the particle size is within the range of 1.1 mu m to 2.0 mu m from D90 to obtain a precursor II;
(3) uniformly mixing the precursor I and the precursor II prepared in the steps (1) and (2) in a horizontal mixer according to the mass ratio of 1:1.2 to obtain a precursor mixture; then, high-temperature sintering is carried out under the condition of nitrogen, the reaction temperature is 640 ℃, the temperature rising efficiency is controlled to be 40 ℃/h, the temperature rising mode is gradually increased, and the sintering time is 22.5 hours;
(4) and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97, and collecting the material to obtain the lithium iron phosphate anode material.
Comparative example 1
A preparation method for synthesizing a lithium iron phosphate composite material by a solid phase method comprises the following steps:
mixing iron phosphate particles and lithium acetate according to the proportion of 1:1.036, stirring uniformly, and then adding 6.9 mass percent of glucose, 4.3 mass percent of methanol and 0.26 mass percent of MgSO 24After fully mixing, grinding for 7.5 hours, drying by using a dryer, and crushing by using a crusher to obtain precursor powder with the particle size of 0.1-D90-0.5 mu m, wherein the mass percentage is based on the precursor powder. Taking a proper amount of precursor powder to sinter at high temperature in a tube furnace: sintering the precursor at high temperature under the condition of nitrogen, wherein the reaction temperature is 640 ℃, the temperature raising efficiency is controlled to be 40 ℃/h, the temperature raising mode is gradually raised, and the sintering time is 22.5 h; and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97 to obtain a finished product of the lithium iron phosphate composite material.
Comparative example 2
A preparation method of liquid-phase synthesized lithium iron phosphate composite material comprises the following steps:
adding lithium hydroxide, phosphoric acid and ferrous sulfate into a reaction kettle according to the molar ratio of 3:1:1, adding a proper amount of carbon nano tube and ethanol, heating at the temperature of 420 ℃, stirring for 125min till the mixture is uniform, reacting to form a complex, drying at the temperature of 120 ℃ by using a dryer, and crushing by using a crusher to obtain precursor powder, wherein the particle size is more than 0.4 and less than D90 and less than 0.6 mu m, and the mass percentage is based on the precursor powder. Taking a proper amount of precursor powder to sinter at high temperature in a tube furnace: sintering the precursor at high temperature under the condition of nitrogen, wherein the reaction temperature is 640 ℃, the temperature raising efficiency is controlled to be 40 ℃/h, the temperature raising mode is gradually raised, and the sintering time is 22.5 h; and (3) performing jet milling on the sintered material by using heated high-temperature compressed air as a milling and drying air source by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, and the milled material has a particle size of 5.15 mu m or less than D97 to obtain a finished product of the lithium iron phosphate composite material.
Comparative example 3
A preparation method of a lithium iron phosphate composite material comprises the following steps:
(1) adding lithium carbonate, ammonium dihydrogen phosphate and ferrous oxalate into a reaction kettle according to a molar ratio of 0.5:1:1, adding a proper amount of glucose and a proper amount of methanol, adjusting the pH to 7.0, heating and stirring at the temperature of 420 ℃ for 125min until the mixture is uniform, reacting to form a complex, drying at the temperature of 120 ℃ by using a dryer, and crushing by using a crusher until the particle size of powder is within the range of 0.2-D90-0.6 mu m to obtain a precursor I;
(2) iron phosphate particles and lithium carbonate are selected to be mixed and stirred uniformly according to the molar ratio of 1:1.036, and glucose with the mass percentage of 6.9%, methanol with the mass percentage of 4.3% and MgSO 0.26% are added4After fully mixing, grinding for 10h, drying at 120 ℃ by using a dryer, and crushing by using a crusher until the particle size is within the range of 0.2 mu m to 1.0 mu m from D90 to obtain a precursor II;
(3) uniformly mixing the precursor I and the precursor II prepared in the steps (1) and (2) in a horizontal mixer according to the mass ratio of 1:1.195 to obtain a precursor mixture; then, high-temperature sintering is carried out in a nitrogen environment, the sintering temperature is 640 ℃, the temperature rising efficiency is controlled to be 40 ℃/h, the temperature rising mode is gradually increased, and the sintering time is 22.5 hours;
(4) and (3) taking the heated high-temperature compressed air as a crushing and drying air source, carrying out jet milling on the sintered material by using a jet mill, wherein the jet temperature is 160 ℃, the rotating speed of the jet mill is 1450rpm, the crushed D97 with the particle size of 5.15 mu m or less is collected, and thus the finished product of the lithium iron phosphate composite material is obtained.
Comparative example 4
A method for preparing a lithium iron phosphate composite material, which is different from the embodiment 1 of the present invention in that: adding doped metal salt in the step (1), and collecting to obtain a finished product of the lithium iron phosphate composite material, wherein other steps are the same as the step 1.
Effect example 1
The LFP products prepared in examples 1 to 4 and comparative examples 1 to 4 were subjected to powder compaction test and electrical property test. Wherein, the powder pressure test is a test result obtained by respectively weighing 1g of each group of LFP finished products under the pressure of 10 MPa. The electrical property test is to obtain the discharge capacity data of the button cell at 0.1C by using each group of LFP finished products under the same condition; see table 1 for specific comparative data; wherein, the lithium iron phosphate positive electrode materials prepared in examples 1 to 4 are experimental groups 1 to 4, respectively; the lithium iron phosphate finished products prepared by the comparative examples 1 to 4 were control groups 1 to 4, respectively.
Table 1: powder pressure test and electrical property test data sheet of each group of samples
| Sample (I) | Powder compacted density (g/cm)3) | Electrical Properties (0.1C/mAh. g)－1) |
| Control group 1 | 2.29 | 153 |
| Control group 2 | 2.28 | 152 |
| Control group 3 | 2.40 | 155 |
| Control group 4 | 2.43 | 154 |
| Experimental group 1 | 2.53 | 160 |
| Experimental group 2 | 2.52 | 162 |
| Experimental group 3 | 2.49 | 161 |
| Experimental group 4 | 2.51 | 162 |
As can be seen from the comparative data, the lithium iron phosphate positive electrode materials prepared in examples 1 to 4 of the present invention have higher compaction density than the lithium iron phosphate composite material finished products prepared by the solid phase method and the liquid phase method in the control groups 1 and 2. And the discharge capacity of 0.1C was significantly increased in the experimental groups 1 to 4, relative to the control group 1 and the control group 2. Therefore, the lithium iron phosphate anode material prepared by the preparation method in the embodiment of the invention has high compaction density, and can effectively increase discharge capacity; the overall performance of the battery composed of the lithium iron phosphate cathode material prepared in the example is higher than that of the batteries prepared in the comparative examples 1 and 2.
Comparative example 3 according to the embodiment of the present invention is substantially performed according to the preparation method described in example 1 of the present invention, and is different in that the particle size of the precursor (ii) in step (2) is made to approach the particle size of the precursor (i) by fine grinding, and the compacted density of the finally obtained product is lower than that of example 1 of the present invention after detection; the overall electrical performance of the cell was also weaker than the product prepared in example 1 of the present invention.
The lithium iron phosphate composite finished product prepared by comparative example 4 of the present invention was prepared by adding the doped metal salt in step (1), and example 1 of the present invention was prepared by adding the doped metal salt in step (2); by comparing the compacted densities of the lithium iron phosphate composite material and the battery and the electrical performance test results of the battery, it is obvious that the compacted density of the finished lithium iron phosphate composite material prepared in the comparative example 4 is lower than that of the product prepared in the example 1; and the overall performance of the battery composed of the finished lithium iron phosphate composite material of comparative example 4 was also lower than that of the battery composed of the lithium iron phosphate positive electrode material prepared in the inventive example 1.
In conclusion, the lithium iron phosphate anode material prepared by the preparation method provided by the invention has the advantages that the doped metal elements are uniformly distributed, and the compaction density is higher; the lithium ion battery prepared by the lithium iron phosphate anode material has the advantages that the migration rate of Li ions is rapidly improved, the concentration polarization of the Li ions in the charging and discharging process is effectively reduced, and the high-rate discharging coulomb efficiency is obviously improved.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the present invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (6)
1. A preparation method of a lithium iron phosphate positive electrode material is characterized by comprising the following steps:
(1) adding a first lithium source, a phosphorus source, an iron source and a first carbon source into a first solvent containing a complexing agent to obtain a mixed solution, uniformly stirring at the temperature of 400-450 ℃, and drying and crushing to obtain a precursor I; the grain diameter of the precursor I is 0.5-0.6 mu m; the pH value of the mixed solution is 7.0-9.0; the complexing agent is citric acid; the molar ratio of the complexing agent to the iron source is (0.5-3) to 1;
(2) uniformly mixing iron phosphate particles and a second lithium source according to a molar ratio of 1 (1.03-1.1), then adding a second carbon source, a second solvent and doped metal salt, fully mixing, grinding for 3-8 hours, and drying and crushing to obtain a precursor II, wherein the mass percentage content of the second carbon source is 2.9-8.7%; the particle size of the precursor (II) is 1.5-2.5 μm; the doped metal salt comprises one or more of magnesium sulfate, aluminum sulfate, titanium nitrate and niobium pentoxide;
(3) placing the precursor I and the precursor II in a mixer according to the mass ratio of 1 (0.5-1.5) and uniformly mixing to obtain a mixed precursor; then sintering at high temperature in an inert or reducing atmosphere to obtain a lithium iron phosphate crude product;
(4) and (3) crushing and drying the crude lithium iron phosphate product in an air flow mill by using the heated high-temperature compressed air as a crushing and drying air source, and then collecting to obtain the lithium iron phosphate anode material.
2. The preparation method according to claim 1, wherein in the step (1), the molar ratio of the first lithium source, the phosphorus source and the iron source is (1-3):1:1, and the mass percentage of the first carbon source is 5% to 10%.
3. The preparation method according to claim 1, wherein the precursor (II) contains the doping metal salt in an amount of 0.12 to 0.41 mass%.
4. The preparation method according to claim 1, wherein the lithium iron phosphate positive electrode material has a D97 particle size of 4 to 8 μm; the compacted density of the lithium iron phosphate anode material is 2.43-2.52g/cm3。
5. The preparation method according to claim 1, wherein in the high-temperature sintering process, the sintering is carried out in a heating mode of 20-40 ℃/h, the sintering temperature is 640 ℃, and the sintering time is 10-25 hours.
6. A lithium ion battery, which is characterized by comprising the lithium iron phosphate cathode material prepared by the preparation method of any one of claims 1 to 5.
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| WO2009117871A1 (en) * | 2008-03-28 | 2009-10-01 | Byd Company Limited | A method of preparing a lithium iron phosphate cathode material for lithium secondary batteries |
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| WO2009117871A1 (en) * | 2008-03-28 | 2009-10-01 | Byd Company Limited | A method of preparing a lithium iron phosphate cathode material for lithium secondary batteries |
| CN102916179A (en) * | 2012-09-29 | 2013-02-06 | 杭州金马能源科技有限公司 | Method for manufacturing industrialized high-energy lithium iron phosphate material |
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