CN115959644A - Method for preparing high-performance lithium iron phosphate by sectional sintering - Google Patents
Method for preparing high-performance lithium iron phosphate by sectional sintering Download PDFInfo
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- CN115959644A CN115959644A CN202211725757.8A CN202211725757A CN115959644A CN 115959644 A CN115959644 A CN 115959644A CN 202211725757 A CN202211725757 A CN 202211725757A CN 115959644 A CN115959644 A CN 115959644A
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- iron phosphate
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- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 title claims abstract description 70
- 238000000034 method Methods 0.000 title claims abstract description 35
- 238000005245 sintering Methods 0.000 title claims abstract description 25
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 67
- 229910052742 iron Inorganic materials 0.000 claims abstract description 31
- 238000001354 calcination Methods 0.000 claims abstract description 27
- 239000002243 precursor Substances 0.000 claims abstract description 26
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims abstract description 24
- 239000002002 slurry Substances 0.000 claims abstract description 24
- 239000002019 doping agent Substances 0.000 claims abstract description 21
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 19
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 19
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 18
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 18
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 15
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims abstract description 14
- 229910052698 phosphorus Inorganic materials 0.000 claims abstract description 14
- 239000011574 phosphorus Substances 0.000 claims abstract description 14
- 239000004408 titanium dioxide Substances 0.000 claims abstract description 12
- 238000001035 drying Methods 0.000 claims abstract description 10
- 229910000398 iron phosphate Inorganic materials 0.000 claims abstract description 10
- 230000008569 process Effects 0.000 claims abstract description 10
- 239000012298 atmosphere Substances 0.000 claims abstract description 8
- 239000000203 mixture Substances 0.000 claims abstract description 8
- 239000002904 solvent Substances 0.000 claims abstract description 5
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 239000002245 particle Substances 0.000 claims description 22
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 16
- 238000010438 heat treatment Methods 0.000 claims description 14
- 239000005955 Ferric phosphate Substances 0.000 claims description 11
- 229940032958 ferric phosphate Drugs 0.000 claims description 11
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims description 11
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 9
- 238000001694 spray drying Methods 0.000 claims description 9
- 239000002994 raw material Substances 0.000 claims description 8
- 239000002202 Polyethylene glycol Substances 0.000 claims description 7
- CZMRCDWAGMRECN-UGDNZRGBSA-N Sucrose Chemical compound O[C@H]1[C@H](O)[C@@H](CO)O[C@@]1(CO)O[C@@H]1[C@H](O)[C@@H](O)[C@H](O)[C@@H](CO)O1 CZMRCDWAGMRECN-UGDNZRGBSA-N 0.000 claims description 7
- 229930006000 Sucrose Natural products 0.000 claims description 7
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 7
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 7
- 229920001223 polyethylene glycol Polymers 0.000 claims description 7
- 239000005720 sucrose Substances 0.000 claims description 7
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 claims description 6
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 claims description 6
- KWGKDLIKAYFUFQ-UHFFFAOYSA-M lithium chloride Chemical compound [Li+].[Cl-] KWGKDLIKAYFUFQ-UHFFFAOYSA-M 0.000 claims description 6
- IIPYXGDZVMZOAP-UHFFFAOYSA-N lithium nitrate Chemical compound [Li+].[O-][N+]([O-])=O IIPYXGDZVMZOAP-UHFFFAOYSA-N 0.000 claims description 6
- SNKMVYBWZDHJHE-UHFFFAOYSA-M lithium;dihydrogen phosphate Chemical compound [Li+].OP(O)([O-])=O SNKMVYBWZDHJHE-UHFFFAOYSA-M 0.000 claims description 6
- 229910052739 hydrogen Inorganic materials 0.000 claims description 4
- 229910052760 oxygen Inorganic materials 0.000 claims description 4
- 229930091371 Fructose Natural products 0.000 claims description 3
- 239000005715 Fructose Substances 0.000 claims description 3
- RFSUNEUAIZKAJO-ARQDHWQXSA-N Fructose Chemical compound OC[C@H]1O[C@](O)(CO)[C@@H](O)[C@@H]1O RFSUNEUAIZKAJO-ARQDHWQXSA-N 0.000 claims description 3
- WQZGKKKJIJFFOK-GASJEMHNSA-N Glucose Natural products OC[C@H]1OC(O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-GASJEMHNSA-N 0.000 claims description 3
- 229910000147 aluminium phosphate Inorganic materials 0.000 claims description 3
- 229960005070 ascorbic acid Drugs 0.000 claims description 3
- 235000010323 ascorbic acid Nutrition 0.000 claims description 3
- 239000011668 ascorbic acid Substances 0.000 claims description 3
- WQZGKKKJIJFFOK-VFUOTHLCSA-N beta-D-glucose Chemical compound OC[C@H]1O[C@@H](O)[C@H](O)[C@@H](O)[C@@H]1O WQZGKKKJIJFFOK-VFUOTHLCSA-N 0.000 claims description 3
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 3
- 229910000388 diammonium phosphate Inorganic materials 0.000 claims description 3
- 235000019838 diammonium phosphate Nutrition 0.000 claims description 3
- SZVJSHCCFOBDDC-UHFFFAOYSA-N ferrosoferric oxide Chemical compound O=[Fe]O[Fe]O[Fe]=O SZVJSHCCFOBDDC-UHFFFAOYSA-N 0.000 claims description 3
- 239000008103 glucose Substances 0.000 claims description 3
- 150000002506 iron compounds Chemical group 0.000 claims description 3
- 229910001386 lithium phosphate Inorganic materials 0.000 claims description 3
- 239000007774 positive electrode material Substances 0.000 claims description 3
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims description 3
- RAQDACVRFCEPDA-UHFFFAOYSA-L ferrous carbonate Chemical compound [Fe+2].[O-]C([O-])=O RAQDACVRFCEPDA-UHFFFAOYSA-L 0.000 claims description 2
- 235000014413 iron hydroxide Nutrition 0.000 claims description 2
- NCNCGGDMXMBVIA-UHFFFAOYSA-L iron(ii) hydroxide Chemical compound [OH-].[OH-].[Fe+2] NCNCGGDMXMBVIA-UHFFFAOYSA-L 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 28
- 239000013078 crystal Substances 0.000 abstract description 11
- BMTOKWDUYJKSCN-UHFFFAOYSA-K iron(3+);phosphate;dihydrate Chemical compound O.O.[Fe+3].[O-]P([O-])([O-])=O BMTOKWDUYJKSCN-UHFFFAOYSA-K 0.000 abstract description 6
- 239000012535 impurity Substances 0.000 abstract description 4
- 238000002360 preparation method Methods 0.000 abstract description 4
- 239000010405 anode material Substances 0.000 abstract description 2
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 10
- 238000000227 grinding Methods 0.000 description 8
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 7
- 229910001416 lithium ion Inorganic materials 0.000 description 6
- 238000012986 modification Methods 0.000 description 5
- 230000004048 modification Effects 0.000 description 5
- 238000001816 cooling Methods 0.000 description 4
- 239000012299 nitrogen atmosphere Substances 0.000 description 4
- 238000010298 pulverizing process Methods 0.000 description 4
- 239000011248 coating agent Substances 0.000 description 3
- 238000000576 coating method Methods 0.000 description 3
- 238000005056 compaction Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- -1 dihydrate ferric phosphate Chemical class 0.000 description 3
- 238000011031 large-scale manufacturing process Methods 0.000 description 3
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 230000002708 enhancing effect Effects 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 238000001228 spectrum Methods 0.000 description 2
- 230000003213 activating effect Effects 0.000 description 1
- 230000004075 alteration Effects 0.000 description 1
- 230000004888 barrier function Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000003795 chemical substances by application Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 238000002425 crystallisation Methods 0.000 description 1
- 230000008025 crystallization Effects 0.000 description 1
- 238000000354 decomposition reaction Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 239000007772 electrode material Substances 0.000 description 1
- 238000004146 energy storage Methods 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 229960004887 ferric hydroxide Drugs 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000011261 inert gas Substances 0.000 description 1
- 230000002401 inhibitory effect Effects 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- WTFXARWRTYJXII-UHFFFAOYSA-N iron(2+);iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[O-2].[Fe+2].[Fe+3].[Fe+3] WTFXARWRTYJXII-UHFFFAOYSA-N 0.000 description 1
- IEECXTSVVFWGSE-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide Chemical compound [OH-].[O-2].[Fe+3] IEECXTSVVFWGSE-UHFFFAOYSA-M 0.000 description 1
- LDHBWEYLDHLIBQ-UHFFFAOYSA-M iron(3+);oxygen(2-);hydroxide;hydrate Chemical compound O.[OH-].[O-2].[Fe+3] LDHBWEYLDHLIBQ-UHFFFAOYSA-M 0.000 description 1
- YPJCVYYCWSFGRM-UHFFFAOYSA-H iron(3+);tricarbonate Chemical compound [Fe+3].[Fe+3].[O-]C([O-])=O.[O-]C([O-])=O.[O-]C([O-])=O YPJCVYYCWSFGRM-UHFFFAOYSA-H 0.000 description 1
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 1
- 238000010902 jet-milling Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 229910021645 metal ion Inorganic materials 0.000 description 1
- 238000003801 milling Methods 0.000 description 1
- 229910052757 nitrogen Inorganic materials 0.000 description 1
- 230000006911 nucleation Effects 0.000 description 1
- 238000010899 nucleation Methods 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 239000008213 purified water Substances 0.000 description 1
- 230000009257 reactivity Effects 0.000 description 1
- 238000007670 refining Methods 0.000 description 1
- 238000001878 scanning electron micrograph Methods 0.000 description 1
- 238000004626 scanning electron microscopy Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Images
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
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- Battery Electrode And Active Subsutance (AREA)
Abstract
The invention discloses a method for preparing high-performance lithium iron phosphate by segmented sintering, which is characterized by comprising the following steps of: s1, mixing iron phosphate dihydrate, a lithium source, a phosphorus source, a carbon source, titanium dioxide and an iron source dopant in a solvent, and sanding the mixture to obtain slurry; s2, drying the slurry to obtain a lithium iron phosphate precursor; and S3, performing three-section high-temperature sectional calcination on the lithium iron phosphate precursor in an inert atmosphere, and then crushing to obtain the high-rate lithium iron phosphate anode material. According to the method, the iron phosphate precursor dihydrate iron phosphate is selected as a main iron source, the precursor preparation step is omitted, the industrial cost is reduced, a proper iron source dopant is added, new impurities are not introduced, the electrical property of the material is improved, the segmented sintering process is adopted, crystal grains are refined, and the comprehensive performance of the lithium iron phosphate material is further improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a method for preparing high-performance lithium iron phosphate by sectional sintering.
Background
Lithium ion batteries are widely used in the fields of automobile power, large-scale energy storage, portable equipment and the like at present as one of marketable products of new energy technology. The lithium iron phosphate becomes a mainstream lithium ion battery anode material by virtue of excellent structural stability, ultra-long cycle service life, excellent safety performance and environmental protection. However, with the application of lithium iron phosphate in the field of power, the electrochemical performance of the lithium iron phosphate is difficult to meet the market demand, and the improvement of the electrical performance of the lithium iron phosphate material on the premise of large-scale production is the key point of future development.
The lithium iron phosphate material is safe, environment-friendly, low in price, high in theoretical capacity as an electrode material, good in structural stability and long in cycle life. However, the material has poor conductivity and low lithium removal/insertion capacity, so that the actual capacity of the material is lower than a theoretical value, and the carbon coating and metal ion doping can effectively improve the conductivity of the lithium iron phosphate and increase the charge-discharge specific capacity of the lithium iron phosphate. The lithium iron phosphate material developed by the iron phosphate process by using a carbothermic method has excellent performance and higher compaction density, but the rate capability of the lithium iron phosphate material still cannot meet the requirements of the power market.
Disclosure of Invention
The invention aims to provide a method for preparing high-performance lithium iron phosphate by sintering in sections to overcome the defects in the prior art.
The purpose of the invention is realized by the following technical scheme:
a method for preparing high-performance lithium iron phosphate by segmented sintering comprises the following steps:
s1, mixing iron phosphate dihydrate, a lithium source, a phosphorus source, a carbon source, titanium dioxide and an iron source dopant in a solvent, and sanding the mixture to obtain slurry; the iron source dopant accounts for 500-10000 ppm of the finished product; the iron source dopant is an iron compound containing one or more elements of C, H, O;
s2, drying the slurry to obtain a lithium iron phosphate precursor;
s3, performing high-temperature sectional calcination on the lithium iron phosphate precursor in an inert atmosphere, and then crushing to obtain a high-rate lithium iron phosphate positive electrode material; the high-temperature sectional calcining process comprises the following steps:
(4) Preserving the heat for 2 to 4 hours at the temperature of between 260 and 290 ℃;
(5) Preserving the heat for 2 to 3 hours at the temperature of between 620 and 680 ℃;
(6) Keeping the temperature for 5-7 h at 720-800 ℃.
Preferably, in the total raw materials in step S1, the molar ratio of total lithium, total iron and total phosphorus is (1.00 to 1.20): (0.93-0.99): 1.
Preferably, the lithium source is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium chloride and lithium dihydrogen phosphate; the phosphorus source is one or a combination of more of phosphoric acid, iron phosphate, lithium dihydrogen phosphate and diammonium hydrogen phosphate.
Preferably, the carbon source is one or more selected from glucose, sucrose, fructose, polyethylene glycol and ascorbic acid.
Preferably, the iron source dopant in step S1 is one or more selected from the group consisting of red iron oxide, yellow iron oxide, black iron oxide, ferric hydroxide and ferric carbonate.
Preferably, the particle diameter of the D50 slurry after sanding in the step S1 is controlled to be 0.30-0.45 μm.
Preferably, in the step S1, the total amount of the carbon source accounts for 10-20% of the mass of the finished lithium iron phosphate, and the amount of the titanium dioxide accounts for 1000-5000 ppm of the mass of the finished product.
Preferably, the drying in the step S2 is spray drying, the air inlet temperature is 180-250 ℃, and the air outlet temperature is 80-110 ℃.
Preferably, the three sections of the high-temperature sectional calcination in the step S3 have heating rates of 1-5 ℃/min, 1-5 ℃/min and 3-15 ℃/min respectively.
Preferably, the pulverization in step S3 is carried out by jet milling, and the particle diameter D50 after the milling is controlled to be 0.8 to 1.5 μm.
According to the method, the iron phosphate precursor dihydrate iron phosphate is selected as a main iron source, the precursor preparation step is omitted, the industrial cost is reduced, a proper iron source dopant is added, new impurities are not introduced, the electrical property of the material is improved, the segmented sintering process is adopted, crystal grains are refined, and the comprehensive performance of the lithium iron phosphate material is further improved. The method is simple to operate, easy to implement and convenient for large-scale production, can be directly improved on the basis of the existing iron phosphate process, and is suitable for large-scale popularization and use.
Drawings
Fig. 1 is an SEM image of a finished lithium iron phosphate product of example 1;
fig. 2 is an XRD pattern of the finished lithium iron phosphate of example 1.
Detailed Description
The invention provides a method for preparing high-performance lithium iron phosphate by sectional sintering, which comprises the following steps:
s1, mixing iron phosphate dihydrate, a lithium source, a phosphorus source, a carbon source, titanium dioxide and an iron source dopant in a solvent, and sanding the mixture to obtain slurry; the iron source dopant accounts for 500-10000 ppm of the finished product; the iron source dopant is an iron compound containing one or more elements of C, H, O;
s2, drying the slurry to obtain a lithium iron phosphate precursor;
s3, performing high-temperature sectional calcination on the lithium iron phosphate precursor in an inert atmosphere, and then crushing to obtain a high-rate lithium iron phosphate positive electrode material; the high-temperature sectional calcining process comprises the following steps:
(7) Preserving the heat for 2 to 4 hours at the temperature of between 260 and 290 ℃;
(8) Preserving the heat for 2 to 3 hours at the temperature of between 620 and 680 ℃;
(9) Keeping the temperature for 5 to 7 hours at the temperature of between 720 and 800 ℃.
The method adopts the ferric phosphate dihydrate and the iron source dopant as the iron source, wherein the ferric phosphate dihydrate is the iron phosphate precursor, and the iron source is selected to save the steps of flash evaporation, roasting, crushing and the like of ferric phosphate preparation. The main element of the dopant is Fe, the other elements are O, H, C and the like, and other impurities cannot be introduced into the lithium iron phosphate finished product after high-temperature reaction. The selected dopant and the dihydrate ferric phosphate are the same iron source, but the dopant and the dihydrate ferric phosphate have different reactivity, so that local defects are formed in the synthesized lithium iron phosphate material, and the charge and discharge performance of the material is enhanced. And the titanium dioxide is added into the raw materials, so that the method has the advantages of inhibiting the growth of crystal grains, improving the conductivity of the material and improving the low-temperature performance of the material. And then, sanding is carried out, so that the raw material slurry is fully dispersed and uniformly mixed, precursor particles are refined, the precursor is uniformly coated by a carbon source, and the product with a proper particle size is obtained after calcination. And drying and calcining to obtain a lithium iron phosphate product.
And the calcination mode selected by the application is sectional gradient calcination, so that the method has the advantages of enhancing the coating effect of the carbon layer and refining grains. The first stage sintering is to evaporate the crystal water from ferric phosphate dihydrate, and the evaporated crystal water is carried away by the inert gas (such as nitrogen) flowing through the roller kiln. The second stage sintering is used for activating the precursor, promoting the nucleation of crystal grains, promoting the decomposition of a carbon source and enhancing the coating effect of the carbon layer. The third stage sintering is to make the raw materials fully react and improve the crystallization degree of crystal grains.
Therefore, the iron phosphate precursor dihydrate iron phosphate is selected as the main iron source, the precursor preparation step is omitted, the industrial cost is reduced, the appropriate iron source dopant is added, new impurities are not introduced, the electrical property of the material is improved, the segmented sintering process is adopted, crystal grains are refined, and the comprehensive performance of the lithium iron phosphate material is further improved. The method is simple to operate, easy to implement and convenient for large-scale production, can be directly improved on the basis of the existing iron phosphate process, and is suitable for large-scale popularization and use.
Preferably, the solvent is purified water.
Preferably, in the total raw materials in step S1, the molar ratio of total lithium, total iron and total phosphorus is (1.00 to 1.20): (0.93-0.99): 1. Of the three raw materials, lithium is slightly excessive according to the chemical formula composition, and iron is conversely less in dosage, the excessive lithium is firstly because lithium is volatilized at high temperature, and part of lithium cannot enter into an ion crystal lattice in an ionic state, so that capacity is lost; meanwhile, the lithium is used as a fluxing agent, and the excessive burning of particles can be inhibited by proper excess, so that the lithium ions in the battery can be removed/inserted. The main function of the small amount of iron is to generate iron vacancies in the crystal lattice so as to reduce the diffusion energy barrier of lithium ions, increase the transmission rate of the lithium ions in a one-dimensional channel and improve the rate capability of the battery. It is worth noting that spray drying is adopted for subsequent drying, if filter pressing drying, ordinary drying in an oven and the like are adopted, more raw material lithium is lost, and therefore the generation amount of lithium iron phosphate is influenced, the loss of spray drying lithium is small, and the air inlet temperature of the spray drying is preferably 180-250 ℃, and the air outlet temperature is preferably 80-110 ℃.
Preferably, the lithium source is one or more selected from lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium chloride, lithium dihydrogen phosphate and the like; the phosphorus source is one or more of phosphoric acid, iron phosphate, lithium dihydrogen phosphate, diammonium hydrogen phosphate and the like.
Preferably, the carbon source is one or more selected from glucose, sucrose, fructose, polyethylene glycol, ascorbic acid and the like.
Preferably, the iron source dopant in step S1 is one or more selected from iron-containing compounds such as iron oxide red, iron oxide yellow, iron oxide black, iron hydroxide and iron carbonate.
Preferably, the particle size of the slurry D50 after sanding in the step S1 is controlled to be 0.30-0.45 μm.
Preferably, in the step S1, the total amount of the carbon source accounts for 10-20% of the mass of the finished lithium iron phosphate, and the amount of the titanium dioxide accounts for 1000-5000 ppm of the mass of the finished product.
Preferably, the three-stage heating rates of the high-temperature stage calcination in the step S3 are respectively 1-5 ℃/min, 1-5 ℃/min and 3-15 ℃/min.
Preferably, the pulverization in step S3 is jet pulverization, and the particle diameter D50 after pulverization is controlled to 0.8 to 1.5. Mu.m. The lithium iron phosphate material is required to have higher pole piece compaction density for obtaining higher energy density (the material evaluation stage is mostly reflected by the powder compaction density side). As a result of practical production experience, controlling the particle size distribution within this range (D50 of about 0.8 to 1.5 μm) helps to achieve higher compacted densities, and excessive or insufficient particle size D50 can result in a loss of compacted density of the material.
Example 1
(1) 5688.2g of ferric phosphate dihydrate, 1275.0g of lithium carbonate, 176.2g of sucrose, 454.4g of polyethylene glycol, 19.0g of titanium dioxide and 11.4g of iron oxide red are respectively weighed and mixed in 12kg of pure water, firstly coarse ground in a coarse grinding machine until the average particle size D50 of the slurry is 1.9 μm, and then fine ground in a fine grinding machine until the average particle size D50 of the slurry is 0.43 μm. Wherein, the molar ratio of the lithium element, the iron element and the phosphorus element is 1.01.
(2) And (2) spray-drying the slurry obtained in the step (1) at the air inlet temperature of 240 ℃ and the air outlet temperature of 90 ℃ to obtain a lithium iron phosphate precursor.
(3) Placing the lithium iron phosphate precursor in a box-type atmosphere furnace, heating to 290 ℃ at the speed of 2 ℃/min for calcining for 3h under the protection of a flowing nitrogen atmosphere, heating to 650 ℃ at the speed of 2 ℃/min for calcining for 2h, and heating to 760 ℃ at the speed of 10 ℃/min for calcining for 5h. After natural cooling, the lithium iron phosphate material is obtained by crushing to an average particle size D50 of 1.1 μm, and SEM and XRD analysis is carried out on a sample, and the results are shown in figures 1 and 2. The XRD spectrum shows that the synthesized material has sharp peak shape and good crystal growth, and the peak spectrum corresponds to lithium iron phosphate. SEM shows that the primary particles of the lithium iron phosphate material are in a sphere-like shape, and the particle size of the primary particles is about 100-200 nm.
Example 2
(1) 4822.4g ferric phosphate dihydrate, 1080.9g lithium carbonate, 149.4g sucrose, 385.2g polyethylene glycol, 16.1g titanium dioxide and 10.9g iron oxide yellow are respectively weighed and mixed in 10kg pure water, firstly coarse ground in a coarse grinding machine until the average particle size D50 of the slurry is 1.8 μm, and then fine ground in a fine grinding machine until the average particle size D50 of the slurry is 0.42 μm. Wherein, the molar ratio of the lithium element, the iron element and the phosphorus element is 1.01.
(2) And (2) spray-drying the slurry obtained in the step (1) at the air inlet temperature of 240 ℃ and the air outlet temperature of 90 ℃ to obtain a lithium iron phosphate precursor.
(3) Placing the lithium iron phosphate precursor in a box-type atmosphere furnace, heating to 290 ℃ at the speed of 2 ℃/min for calcining for 3h under the protection of a flowing nitrogen atmosphere, heating to 650 ℃ at the speed of 2 ℃/min for calcining for 2h, and heating to 760 ℃ at the speed of 10 ℃/min for calcining for 5h. And after natural cooling, crushing the mixture to obtain the lithium iron phosphate material, wherein the average particle size D50 of the lithium iron phosphate material is 1.0 mu m.
Example 3
(1) 5341.2g of ferric phosphate dihydrate, 1206.2g of lithium carbonate, 167.2g of sucrose, 431.2g of polyethylene glycol, 18.7g of titanium dioxide and 15.8g of iron oxide red are respectively weighed and mixed in 11kg of pure water, firstly coarse ground in a coarse grinding machine until the average grain size D50 of the slurry is 1.9 μm, and then fine ground in a fine grinding machine until the average grain size D50 of the slurry is 0.42 μm. Wherein, the molar ratio of the lithium element, the iron element and the phosphorus element is 1.01.
(2) And (2) spray-drying the slurry obtained in the step (1) at the air inlet temperature of 240 ℃ and the air outlet temperature of 90 ℃ to obtain a lithium iron phosphate precursor.
(3) Placing the lithium iron phosphate precursor in a box-type atmosphere furnace, heating to 270 ℃ at the speed of 2 ℃/min for calcining for 3h under the protection of a flowing nitrogen atmosphere, heating to 680 ℃ at the speed of 2 ℃/min for calcining for 2h, and heating to 790 ℃ at the speed of 10 ℃/min for calcining for 5h. And after natural cooling, crushing the mixture to obtain the lithium iron phosphate material, wherein the average particle size D50 of the lithium iron phosphate material is 1.2 mu m.
Comparative example 1
This comparative example is compared with example 1, with the difference that no iron-containing dopant was added in step (1) and only two-stage sintering was carried out in step (3), the sintering process being specifically: heating to 290 ℃ at the speed of 2 ℃/min, calcining for 3h at constant temperature, heating to 760 ℃ at the speed of 2 ℃/min, and calcining for 7h at constant temperature.
(1) 5688.2g of ferric phosphate dihydrate, 1275.0g of lithium carbonate, 176.2g of sucrose, 454.4g of polyethylene glycol and 19.0g of titanium dioxide are respectively weighed and mixed in 12kg of pure water, firstly ground in a coarse grinding machine until the average particle size D50 of the slurry is 1.8 μm, and then ground in a fine grinding machine until the average particle size D50 of the slurry is 0.40 μm. Wherein, the molar ratio of the lithium element, the iron element and the phosphorus element is 1.02.
(2) Spray drying the slurry obtained in the step (1) at the air inlet temperature of 240 ℃ and the air outlet temperature of 90 ℃ to obtain a lithium iron phosphate precursor;
(3) And placing the lithium iron phosphate precursor into a box-type atmosphere furnace, calcining at 290 ℃ for 3h under the protection of a flowing nitrogen atmosphere, and calcining at 760 ℃ for 7h. And after natural cooling, crushing the mixture to obtain the lithium iron phosphate material, wherein the average particle size D50 of the lithium iron phosphate material is 1.1 mu m.
The results of the performance tests of the lithium iron phosphate samples obtained in examples 1 to 3 and comparative example 1 are shown in table 1.
TABLE 1 comparison of lithium iron phosphate Performance for each example
While preferred embodiments of the present invention have been described, additional variations and modifications in those embodiments may occur to those skilled in the art once they learn of the basic inventive concepts. Therefore, it is intended that the appended claims be interpreted as including preferred embodiments and all such alterations and modifications as fall within the scope of the invention. It will be apparent to those skilled in the art that various changes and modifications may be made in the present invention without departing from the spirit and scope of the invention. Thus, if such modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include such modifications and variations.
Claims (10)
1. A method for preparing high-performance lithium iron phosphate by segmented sintering is characterized by comprising the following steps:
s1, mixing ferric phosphate dihydrate, a lithium source, a phosphorus source, a carbon source, titanium dioxide and an iron source dopant in a solvent, and sanding the mixture to obtain slurry; the iron source dopant accounts for 500-10000 ppm of the finished product; the iron source dopant is an iron compound containing one or more elements of C, H, O;
s2, drying the slurry to obtain a lithium iron phosphate precursor;
s3, performing high-temperature sectional calcination on the lithium iron phosphate precursor in an inert atmosphere, and then crushing to obtain a high-rate lithium iron phosphate positive electrode material; the high-temperature sectional calcining process comprises the following steps:
(1) Preserving the heat for 2 to 4 hours at the temperature of between 260 and 290 ℃;
(2) Preserving the heat for 2 to 3 hours at the temperature of between 620 and 680 ℃;
(3) Keeping the temperature for 5 to 7 hours at the temperature of between 720 and 800 ℃.
2. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
in all raw materials in the step S1, the molar ratio of total lithium to total iron to total phosphorus is (1.00-1.20): (0.93-0.99) 1.
3. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
the lithium source is one or more of lithium carbonate, lithium hydroxide, lithium phosphate, lithium nitrate, lithium chloride and lithium dihydrogen phosphate; the phosphorus source is one or more of phosphoric acid, iron phosphate, lithium dihydrogen phosphate and diammonium hydrogen phosphate.
4. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
the carbon source is one or more of glucose, sucrose, fructose, polyethylene glycol and ascorbic acid.
5. The method for preparing high-performance lithium iron phosphate by fractional sintering according to claim 1,
and the iron source dopant in the step S1 is one or a combination of more of iron oxide red, iron oxide yellow, iron oxide black, iron hydroxide and iron carbonate.
6. The method for preparing high-performance lithium iron phosphate by fractional sintering according to claim 1,
and (2) controlling the particle size of the slurry D50 to be 0.30-0.45 mu m after sanding in the step S1.
7. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
s1, the total consumption of the carbon source accounts for 10-20% of the mass of the finished lithium iron phosphate, and the consumption of the titanium dioxide accounts for 1000-5000 ppm of the mass of the finished product.
8. The method for preparing high-performance lithium iron phosphate by the step sintering according to claim 2,
and S2, spray drying is adopted for drying, the air inlet temperature is 180-250 ℃, and the air outlet temperature is 80-110 ℃.
9. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
and the three sections of heating rates of the high-temperature sectional calcination in the step S3 are respectively 1-5 ℃/min, 1-5 ℃/min and 3-15 ℃/min.
10. The method for preparing high-performance lithium iron phosphate by segment sintering according to claim 1,
and step S3, the crushing mode is jet crushing, and the particle size D50 after crushing is controlled to be 0.8-1.5 mu m.
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