CN113772650B - Preparation method and application of lithium iron phosphate - Google Patents
Preparation method and application of lithium iron phosphate Download PDFInfo
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- CN113772650B CN113772650B CN202111107692.6A CN202111107692A CN113772650B CN 113772650 B CN113772650 B CN 113772650B CN 202111107692 A CN202111107692 A CN 202111107692A CN 113772650 B CN113772650 B CN 113772650B
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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 102
- 238000002360 preparation method Methods 0.000 title claims abstract description 31
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims abstract description 58
- 238000000034 method Methods 0.000 claims abstract description 53
- 239000000463 material Substances 0.000 claims abstract description 46
- 239000011268 mixed slurry Substances 0.000 claims abstract description 42
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 37
- 239000005955 Ferric phosphate Substances 0.000 claims abstract description 30
- 229940032958 ferric phosphate Drugs 0.000 claims abstract description 30
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims abstract description 30
- 239000002245 particle Substances 0.000 claims abstract description 28
- 238000003786 synthesis reaction Methods 0.000 claims abstract description 28
- 230000008569 process Effects 0.000 claims abstract description 26
- 229910052742 iron Inorganic materials 0.000 claims abstract description 25
- 229910019142 PO4 Inorganic materials 0.000 claims abstract description 23
- 239000012065 filter cake Substances 0.000 claims abstract description 23
- 239000010452 phosphate Substances 0.000 claims abstract description 23
- 238000005406 washing Methods 0.000 claims abstract description 23
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 claims abstract description 22
- 239000000203 mixture Substances 0.000 claims abstract description 21
- 235000003891 ferrous sulphate Nutrition 0.000 claims abstract description 20
- 239000011790 ferrous sulphate Substances 0.000 claims abstract description 20
- 229910000359 iron(II) sulfate Inorganic materials 0.000 claims abstract description 20
- 238000001035 drying Methods 0.000 claims abstract description 19
- 239000011812 mixed powder Substances 0.000 claims abstract description 19
- 238000001354 calcination Methods 0.000 claims abstract description 18
- 238000002156 mixing Methods 0.000 claims abstract description 17
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 claims abstract description 16
- 229910001416 lithium ion Inorganic materials 0.000 claims abstract description 16
- 230000032683 aging Effects 0.000 claims abstract description 12
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N iron oxide Inorganic materials [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims abstract description 10
- NDLPOXTZKUMGOV-UHFFFAOYSA-N oxo(oxoferriooxy)iron hydrate Chemical compound O.O=[Fe]O[Fe]=O NDLPOXTZKUMGOV-UHFFFAOYSA-N 0.000 claims abstract description 10
- 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 abstract description 9
- 239000008103 glucose Substances 0.000 claims abstract description 9
- 238000000227 grinding Methods 0.000 claims abstract description 9
- 229910018119 Li 3 PO 4 Inorganic materials 0.000 claims abstract description 8
- 238000012216 screening Methods 0.000 claims abstract description 8
- 239000007788 liquid Substances 0.000 claims abstract description 4
- 238000004321 preservation Methods 0.000 claims abstract description 4
- 238000000926 separation method Methods 0.000 claims abstract description 3
- 238000006243 chemical reaction Methods 0.000 claims description 27
- 229910052698 phosphorus Inorganic materials 0.000 claims description 20
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 20
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 16
- 238000001694 spray drying Methods 0.000 claims description 16
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 claims description 15
- 239000011574 phosphorus Substances 0.000 claims description 15
- 239000006227 byproduct Substances 0.000 claims description 13
- 238000001914 filtration Methods 0.000 claims description 12
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 11
- SURQXAFEQWPFPV-UHFFFAOYSA-L iron(2+) sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Fe+2].[O-]S([O-])(=O)=O SURQXAFEQWPFPV-UHFFFAOYSA-L 0.000 claims description 11
- 238000004519 manufacturing process Methods 0.000 claims description 11
- 235000010215 titanium dioxide Nutrition 0.000 claims description 11
- 239000013078 crystal Substances 0.000 claims description 9
- 230000001681 protective effect Effects 0.000 claims description 9
- 229910052757 nitrogen Inorganic materials 0.000 claims description 8
- 229910000398 iron phosphate Inorganic materials 0.000 claims description 7
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 claims description 6
- MNNHAPBLZZVQHP-UHFFFAOYSA-N diammonium hydrogen phosphate Chemical compound [NH4+].[NH4+].OP([O-])([O-])=O MNNHAPBLZZVQHP-UHFFFAOYSA-N 0.000 claims description 6
- 238000010438 heat treatment Methods 0.000 claims description 6
- 239000004254 Ammonium phosphate Substances 0.000 claims description 4
- 229910000148 ammonium phosphate Inorganic materials 0.000 claims description 4
- 235000019289 ammonium phosphates Nutrition 0.000 claims description 4
- 229940116007 ferrous phosphate Drugs 0.000 claims description 4
- 229910000155 iron(II) phosphate Inorganic materials 0.000 claims description 4
- SDEKDNPYZOERBP-UHFFFAOYSA-H iron(ii) phosphate Chemical compound [Fe+2].[Fe+2].[Fe+2].[O-]P([O-])([O-])=O.[O-]P([O-])([O-])=O SDEKDNPYZOERBP-UHFFFAOYSA-H 0.000 claims description 4
- 229910001209 Low-carbon steel Inorganic materials 0.000 claims description 3
- 229910052786 argon Inorganic materials 0.000 claims description 3
- CWYNVVGOOAEACU-UHFFFAOYSA-N Fe2+ Chemical compound [Fe+2] CWYNVVGOOAEACU-UHFFFAOYSA-N 0.000 claims description 2
- 229910001448 ferrous ion Inorganic materials 0.000 claims description 2
- 229910052734 helium Inorganic materials 0.000 claims description 2
- 239000001307 helium Substances 0.000 claims description 2
- SWQJXJOGLNCZEY-UHFFFAOYSA-N helium atom Chemical compound [He] SWQJXJOGLNCZEY-UHFFFAOYSA-N 0.000 claims description 2
- 239000002105 nanoparticle Substances 0.000 claims description 2
- 230000009467 reduction Effects 0.000 claims description 2
- 150000003013 phosphoric acid derivatives Chemical class 0.000 claims 1
- BAUYGSIQEAFULO-UHFFFAOYSA-L iron(2+) sulfate (anhydrous) Chemical compound [Fe+2].[O-]S([O-])(=O)=O BAUYGSIQEAFULO-UHFFFAOYSA-L 0.000 abstract description 18
- 230000015572 biosynthetic process Effects 0.000 abstract description 16
- 238000009826 distribution Methods 0.000 abstract description 8
- 239000010405 anode material Substances 0.000 abstract description 6
- 230000008901 benefit Effects 0.000 description 11
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 10
- 102220043159 rs587780996 Human genes 0.000 description 10
- 229910052799 carbon Inorganic materials 0.000 description 9
- 238000005056 compaction Methods 0.000 description 9
- 239000007774 positive electrode material Substances 0.000 description 9
- 230000000052 comparative effect Effects 0.000 description 8
- 238000001514 detection method Methods 0.000 description 8
- 238000004806 packaging method and process Methods 0.000 description 7
- 238000001878 scanning electron micrograph Methods 0.000 description 7
- 239000000843 powder Substances 0.000 description 6
- 238000003756 stirring Methods 0.000 description 6
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 5
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 5
- 235000011114 ammonium hydroxide Nutrition 0.000 description 5
- 238000011946 reduction process Methods 0.000 description 5
- 239000002351 wastewater Substances 0.000 description 5
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 4
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 4
- LFVGISIMTYGQHF-UHFFFAOYSA-N ammonium dihydrogen phosphate Chemical compound [NH4+].OP(O)([O-])=O LFVGISIMTYGQHF-UHFFFAOYSA-N 0.000 description 4
- 229910000387 ammonium dihydrogen phosphate Inorganic materials 0.000 description 4
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 4
- 229910052808 lithium carbonate Inorganic materials 0.000 description 4
- 235000019837 monoammonium phosphate Nutrition 0.000 description 4
- 239000007800 oxidant agent Substances 0.000 description 4
- 230000001590 oxidative effect Effects 0.000 description 4
- 230000001698 pyrogenic effect Effects 0.000 description 4
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 description 3
- 239000003337 fertilizer Substances 0.000 description 3
- 238000003837 high-temperature calcination Methods 0.000 description 3
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 description 3
- YOBAEOGBNPPUQV-UHFFFAOYSA-N iron;trihydrate Chemical compound O.O.O.[Fe].[Fe] YOBAEOGBNPPUQV-UHFFFAOYSA-N 0.000 description 3
- 229910052744 lithium Inorganic materials 0.000 description 3
- 230000004048 modification Effects 0.000 description 3
- 238000012986 modification Methods 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000004064 recycling Methods 0.000 description 3
- 238000012360 testing method Methods 0.000 description 3
- 229910000388 diammonium phosphate Inorganic materials 0.000 description 2
- 235000019838 diammonium phosphate Nutrition 0.000 description 2
- 238000005265 energy consumption Methods 0.000 description 2
- 238000004146 energy storage Methods 0.000 description 2
- 238000005516 engineering process Methods 0.000 description 2
- 230000007613 environmental effect Effects 0.000 description 2
- 238000003912 environmental pollution Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 238000010902 jet-milling Methods 0.000 description 2
- 229910001386 lithium phosphate Inorganic materials 0.000 description 2
- 239000011164 primary particle Substances 0.000 description 2
- 238000001223 reverse osmosis Methods 0.000 description 2
- 239000013589 supplement Substances 0.000 description 2
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 description 2
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- 239000005696 Diammonium phosphate Substances 0.000 description 1
- 229910010710 LiFePO Inorganic materials 0.000 description 1
- BFNBIHQBYMNNAN-UHFFFAOYSA-N ammonium sulfate Chemical compound N.N.OS(O)(=O)=O BFNBIHQBYMNNAN-UHFFFAOYSA-N 0.000 description 1
- 229910052921 ammonium sulfate Inorganic materials 0.000 description 1
- 235000011130 ammonium sulphate Nutrition 0.000 description 1
- 238000000498 ball milling Methods 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 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 description 1
- 238000004364 calculation method Methods 0.000 description 1
- 238000003763 carbonization Methods 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000011248 coating agent Substances 0.000 description 1
- 238000000576 coating method Methods 0.000 description 1
- 230000018044 dehydration Effects 0.000 description 1
- 238000006297 dehydration reaction Methods 0.000 description 1
- 238000009831 deintercalation Methods 0.000 description 1
- 238000011161 development Methods 0.000 description 1
- 230000018109 developmental process Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 239000000706 filtrate Substances 0.000 description 1
- 238000010304 firing Methods 0.000 description 1
- 239000013505 freshwater Substances 0.000 description 1
- 229910052739 hydrogen Inorganic materials 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- -1 iron ion Chemical class 0.000 description 1
- 239000006012 monoammonium phosphate Substances 0.000 description 1
- 239000010450 olivine Substances 0.000 description 1
- 229910052609 olivine Inorganic materials 0.000 description 1
- 239000003208 petroleum Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 230000035484 reaction time Effects 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 239000010865 sewage Substances 0.000 description 1
- 238000007873 sieving Methods 0.000 description 1
- 238000003746 solid phase reaction Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 230000002194 synthesizing effect Effects 0.000 description 1
- 238000004065 wastewater treatment Methods 0.000 description 1
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- C01—INORGANIC CHEMISTRY
- C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
- C01B25/26—Phosphates
- C01B25/45—Phosphates containing plural metal, or metal and ammonium
-
- H—ELECTRICITY
- 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
- H01M10/052—Li-accumulators
- H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
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- 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
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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Abstract
The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a preparation method and application of lithium iron phosphate. The preparation method comprises the following steps: mixing ferrous sulfate solution and phosphate solution, carrying out synthesis reaction, ageing the solution after the synthesis reaction, carrying out solid-liquid separation on the aged solution, washing a filter cake, drying, calcining, crushing, screening and removing iron to obtain an anhydrous ferric phosphate and ferric oxide mixture; mixing the mixture and Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, grinding the mixed slurry to obtain nano-scale mixed slurry, and drying the nano-scale mixed slurry to obtain mixed powder material; and (3) roasting the mixed powder material at 700-800 ℃ under heat preservation, and crushing to obtain the lithium iron phosphate. The method realizes one-step synthesis of anhydrous ferric phosphate in an inorganic system, and the obtained anhydrous ferric phosphate has good dispersibility and uniform particle size distribution, and is convenient for controlling the process of the rear-end lithium iron phosphate and optimizing the performance parameters.
Description
Technical Field
The invention relates to the technical field of preparation of lithium ion battery anode materials, in particular to a preparation method and application of lithium iron phosphate.
Background
With the increasing exhaustion of petroleum resources, development of electric automobiles is imperative. At present, the most critical technology of electric vehicles is to develop a secondary battery which is cheap, safe and environment-friendly. Lithium ion batteries are recognized as the best candidates for electric vehicle power batteries because of their combination of high voltage, high specific energy, high power, and the like. For lithium ion batteries, the positive electrode material is a key factor in determining its electrochemical performance, safety performance, energy density, and price cost. Goodenough et al reported olivine LiFePO for the first time in 1997 4 Is a reversible lithium intercalation-deintercalation characteristic. The lithium ion battery anode material has the advantages of good safety performance, long cycle life, wide raw material sources, environmental friendliness and the like, and is always a hot spot for research and development of the lithium ion battery anode material.
The main current technology of lithium iron phosphate is to use anhydrous ferric phosphate as a precursor, and the anhydrous ferric phosphate is adopted to synthesize the lithium iron phosphate, which has the following advantages: 1. the operation process is simple, and the industrialization maturity is high; 2. the obtained lithium iron phosphate has high capacity and high compaction density; 3. the safety performance is good; 4 cycle life is long.
At present, conventional lithium iron phosphate synthesis generally adopts ferrous salt, phosphate and oxidant to synthesize ferric phosphate dihydrate, then the ferric phosphate dihydrate is baked and calcined at high temperature to obtain anhydrous ferric phosphate, then the anhydrous ferric phosphate, lithium carbonate, glucose and pure water are mixed according to a certain proportion, and then ball sanding, spray drying, high-temperature calcination (nitrogen protection), jet milling, iron removal and packaging are carried out to obtain the battery-grade lithium iron phosphate. The process has high maturity and is widely used. However, it has the following disadvantages:
firstly, environmental protection pressure is big in anhydrous ferric phosphate production process, and waste water treatment cost is high, and according to statistics, every ton ferric phosphate produces nearly seventy tons of waste water, and wherein contains some pollution factors such as sulfate radical, phosphate radical, ammonium root, iron ion, etc. the handling capacity is big, and the treatment cost is high.
Secondly, the anhydrous ferric phosphate production process flow is long, and the flow comprises the flow of ferric phosphate dihydrate synthesis, washing, drying, high-temperature calcination dehydration and the like, so that equipment investment is large, labor cost and energy consumption are high, and the cost of the final anhydrous ferric phosphate product is high, so that the cost of lithium iron phosphate is high.
Thirdly, lithium iron phosphate is expensive in production by lithium carbonate, and the energy consumption and the cost in the production process are high.
In view of this, the present invention has been made.
Disclosure of Invention
The first aim of the invention is to provide a preparation method of lithium iron phosphate, which is simple, has short flow, realizes a one-step synthesis process of anhydrous ferric phosphate in an inorganic system, does not use steam and oxidant in the process, has simple process flow, small wastewater production amount and low cost, and the obtained anhydrous ferric phosphate has good dispersibility and uniform particle size distribution. Meanwhile, in the pyrogenic process synthesis stage of the lithium iron phosphate material, low-cost Li is adopted 3 PO 4 And H 3 PO 4 Li which is commonly used as substitute material and has higher price 2 CO 3 The lithium ion battery anode material lithium iron phosphate prepared by the method has lower cost,the compaction density, specific capacity and other comprehensive properties of the material are guaranteed.
The second purpose of the invention is to provide the application of the lithium iron phosphate prepared by the preparation method of the lithium iron phosphate in the preparation of the lithium ion battery anode, so that the process flow is simplified, the preparation cost is saved, and the prepared lithium ion battery anode has high compacted density and specific capacity.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
a method for preparing lithium iron phosphate, comprising the following steps:
(a) Mixing ferrous sulfate solution with phosphate solution and carrying out synthesis reaction, ageing the solution after the synthesis reaction, carrying out solid-liquid separation on the aged solution, washing a filter cake, drying, calcining, crushing, screening and removing iron to obtain an anhydrous ferric phosphate and ferric oxide mixture;
(b) Mixing the mixture obtained in step (a) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, grinding the mixed slurry to obtain nano-scale mixed slurry, and drying the nano-scale mixed slurry to obtain mixed powder material;
(c) And (c) roasting the mixed powder material obtained in the step (b) at 700-800 ℃ and crushing to obtain lithium iron phosphate.
The preparation method of the lithium iron phosphate provided by the invention is simple and easy to implement, has short flow, realizes a one-step synthesis process of anhydrous ferric phosphate in an inorganic system, does not use steam and oxidant in the process, has the advantages of simplified process flow, small wastewater production amount and low cost, and the obtained anhydrous ferric phosphate has good dispersibility and uniform particle size distribution. Meanwhile, in the pyrogenic process synthesis stage of the lithium iron phosphate material, low-cost Li is adopted 3 PO 4 And H 3 PO 4 Li which is commonly used as substitute material and has higher price 2 CO 3 The lithium ion battery anode material lithium iron phosphate prepared by the method has lower cost and ensures the comprehensive properties of compact density, specific capacity and the like.
The main chemical reactions involved in the preparation method are as follows:
3FeSO 4 +2NH 4 H 2 PO 4 +4NH 3 H 2 O+4H 2 O→Fe 3 (PO 4 ) 2 ·8H 2 O↓+3(NH 4 ) 2 SO 4 ；
4Fe 3 (PO 4 ) 2 ·8H 2 O+3O 2 →8FePO 4 +2Fe 2 O 3 +32H 2 O；
8FePO 4 +2Fe 2 O 3 +3C+4Li 3 PO 4 →12LiFePO 4 +3CO 2 。
the first step of synthesizing ferrous phosphate, namely controlling the concentration, temperature, pH and mixing speed of a ferrous sulfate solution and a phosphate solution, and controlling the stirring speed, temperature and time after the ferrous sulfate solution and the phosphate solution enter a reaction kettle, so that a pure ferrous phosphate precipitate is obtained, and steam and ferrous ions are not required to be oxidized in the process.
And washing the obtained ferrous phosphate, and then drying, calcining, screening and removing iron to obtain the battery-grade anhydrous ferric phosphate and ferric oxide mixture, wherein the battery-grade anhydrous ferric phosphate and ferric oxide mixture has good dispersibility, high purity and uniform particle size distribution. Wherein, an electromagnetic dry powder iron remover with medium node field intensity as high as 13000GS is adopted for concentrated iron removal, and magnetic impurities (Fe) in the product are less than or equal to 0.5ppm.
The obtained filtrate and the washing liquid are treated step by step, the wastewater is concentrated through RO (reverse osmosis), the water cost is saved by recycling the produced fresh water, and the concentrated water is subjected to MVR (multiple effect evaporation) system to obtain byproducts of ammonium sulfate and ammonium phosphate which are high-quality fertilizer raw materials, so that the method can be used for agricultural organic fertilizers and water-soluble fertilizers, and half of the sewage treatment cost is recovered.
In the second step, in the pyrogenic synthesis stage of lithium iron phosphate material, low-cost Li is adopted 3 PO 4 And H 3 PO 4 Li which is commonly used as substitute material and has higher price 2 CO 3 The battery-grade lithium iron phosphate is obtained through ball milling, spray drying, high-temperature calcination (nitrogen protection), jet milling, iron removal and packaging.
The battery grade lithium phosphate used by the obtained lithium iron phosphate material not only solves the problem of lithium source, but also supplements a phosphorus source, and the material cost is lower than that of the battery grade lithium carbonate by more than 20 percent. Compared with the traditional process, the obtained lithium iron phosphate material has more coordinated compaction density and specific capacity and has a certain improvement.
The value of the byproduct of the anhydrous ferric phosphate is calculated through comprehensive calculation, the cost of each ton of ferric phosphate is lower than 5000 yuan by adopting the process, and the cost of each ton of ferric phosphate of the conventional process is generally 8000-10000 yuan, so that the price advantage is very obvious; the cost of each ton of lithium iron phosphate is lower than 17000 yuan, the current power type lithium iron phosphate is 3.5-3.7 ten thousand yuan/ton, the energy storage type is 2.5-2.8 ten thousand yuan/ton, and the overall price advantage is very obvious.
Preferably, the mixed powder material obtained in the step (b) is baked at 720-780 ℃ in a heat preservation way, and 730 ℃, 740 ℃, 750 ℃, 760 ℃ or 770 ℃ can be selected.
Preferably, in the step (a), the ferrous sulfate solution is prepared by dissolving, reducing, filtering and clarifying titanium white byproduct ferrous sulfate heptahydrate crystals.
The used ferrous sulfate heptahydrate crystal is a titanium white byproduct, and the problems of reasonable recycling of resources are effectively solved and the production cost is reduced due to the large amount of the titanium white byproduct, low utilization value and serious environmental pollution.
Preferably, iron powder or mild steel is used during the reduction and the pH of the solution is maintained = 3.5-4.5; the pH of the solution may also be selected to be 3.7, 3.8, 3.9, 4.1, 4.2, 4.3 or 4.4.
Preferably, the concentration of the ferrous sulfate solution is 250-310g/L, and 260g/L, 270g/L, 280g/L, 290g/L, 300g/L or 305g/L can be selected.
Preferably, in step (a), the phosphate comprises at least one of ammonium phosphate, diammonium phosphate and monoammonium phosphate.
Preferably, the pH of the phosphate solution is = 7.0-9.0; it is also possible to select 7.5, 7.8, 8.2, 8.5 or 8.8.
Preferably, the phosphate solution has a phosphorus mass concentration of 8% -12%, alternatively 8.5%, 9%, 9.5%, 10%, 10.5% or 11%.
Preferably, in the step (a), during the synthesis reaction, the molar ratio of iron to phosphorus in the reaction solution system is 0.97 to 1.0, and 0.98 or 0.99 may be selected.
Preferably, in the step (a), the temperature of the reaction solution system is 45-55deg.C, and optionally 46, 47, 49, 51, 53, and 55 ℃ during the synthesis reaction; more preferably, the synthesis reaction time is 60-80min, and 65min, 68min, 71min, 74min, 77min or 79min can be selected.
Preferably, in step (a), the temperature of the solution system is 90-98 ℃, optionally 91 ℃, 92 ℃, 93 ℃, 94 ℃, 95 ℃, 96 ℃ or 97 ℃ during the aging process; more preferably, the solution system is heated with steam.
Preferably, in step (a), the aging time is 2-4 hours, and may be 2.5 hours, 3 hours or 3.5 hours.
Preferably, in step (a), the drying is flash drying.
Preferably, in step (a), the washed filter cake is washed with pure water, the end point pH of the washing is=3.3±0.5, and the conductivity is less than or equal to 300us.
Preferably, the calcination temperature is 550-600 ℃, 560 ℃, 570 ℃, 580 ℃ or 590 ℃ can be selected, and the time is 2-3h, 2.5h can be selected; more preferably, the temperature of the calcination is 560-590 ℃.
Preferably, the specific surface area ssa=8.0-10.0 m of the anhydrous iron phosphate and iron sesquioxide mixture 2 /g, optionally 8.5m 2 /g、9.0m 2 /g or 9.5m 2 Per g, particle size d50=3-5 μm, optionally 4 μm.
Preferably, in the step (b), the molar ratio of each element in the mixed slurry is P, fe, li, C=1.0 (0.97-1.00), 1.00-1.05 and 0.40-0.50.
Preferably, in step (b), the pH of the mixed slurry is = 8.0-10.0; 8.5, 8.8, 9.1, 9.4 or 9.8 may also be selected.
Preferably, in the step (b), the particle size of the nano-sized mixed slurry is d50.ltoreq.0.4 μm.
Preferably, in step (b), the particle size d50=10-30 μm of the mixed powder material may also be selected from 12 μm, 16 μm, 18 μm, 21 μm, 25 μm or 27 μm.
Preferably, in step (b), the drying is spray drying, the inlet air temperature of the spray drying is 200-250 ℃, and 210 ℃, 220 ℃, 230 ℃, 240 ℃ or 245 ℃ can be selected; the air outlet temperature is 85-90deg.C, 86 deg.C, 88 deg.C or 89 deg.C can be selected.
Preferably, in step (c), the time of the insulated firing is 6 to 12 hours; it is also possible to select 7h, 8h, 9h, 10h or 11h.
In the heat preservation roasting process, high-temperature solid phase reaction and carbonization reaction occur to generate the lithium iron phosphate material with an intact coated carbon layer.
Preferably, the process of insulating roasting is carried out under a protective atmosphere; more preferably, the protective atmosphere comprises at least one of nitrogen, argon and helium.
Preferably, in the step (c), the particle size d50= (1.1±0.5) μm of the lithium iron phosphate may be 0.7 μm, 0.9 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm.
The application also provides application of the lithium iron phosphate prepared by the preparation method of the lithium iron phosphate in preparation of a positive electrode of a lithium ion battery. The method can simplify the process flow for preparing the anode of the lithium ion battery, save the cost of the prepared raw materials, and improve the compaction density and specific capacity of the prepared anode of the lithium ion battery.
Compared with the prior art, the invention has the beneficial effects that:
(1) The preparation method of the lithium iron phosphate provided by the invention is simple and easy to implement, has a short flow, can realize one-step synthesis of anhydrous ferric phosphate in an inorganic system, does not use steam and oxidant in the synthesis process, simplifies the process flow, has small wastewater production amount, effectively reduces the cost, and adopts the preparation methodThe anhydrous ferric phosphate prepared by the method has good dispersibility and more uniform particle size distribution. Meanwhile, in the pyrogenic process synthesis stage of the lithium iron phosphate material, low-cost Li is adopted 3 PO 4 And H 3 PO 4 Li which is commonly used as substitute material and has higher price 2 CO 3 The cost is lower, and the comprehensive properties of the material such as compaction density, specific capacity and the like are guaranteed.
(2) The battery grade anhydrous ferric phosphate and ferric oxide mixture prepared by the preparation method provided by the invention has the advantages of good dispersibility, high purity, uniform particle size distribution and the like.
(3) According to the preparation method of the lithium iron phosphate, the ferrous sulfate heptahydrate crystal is adopted as the titanium white byproduct, and the problems of reasonable recycling of resources are effectively solved due to the fact that the titanium white byproduct is large in quantity, low in utilization value and serious in environmental pollution.
(4) According to the preparation method of the lithium iron phosphate, the battery-grade lithium phosphate used by the obtained lithium iron phosphate material not only solves the problem of a lithium source, but also supplements a phosphorus source, and the material cost is lower than that of the battery-grade lithium carbonate by more than 20 percent. Compared with the traditional process, the obtained lithium iron phosphate material has more coordinated compaction density and specific capacity and has a certain improvement.
(5) According to the preparation method of the lithium iron phosphate, the cost of each ton of ferric phosphate is lower than 5000 yuan, and compared with the conventional process, the cost of each ton of ferric phosphate is reduced by 3000-5000 yuan, and the price advantage is very obvious; in addition, the cost of each ton of lithium iron phosphate is lower than 17000 yuan, the current power type lithium iron phosphate is 3.5-3.7 ten thousand yuan/ton, the energy storage type is 2.5-2.8 ten thousand yuan/ton, and the overall price advantage is very obvious.
(6) The invention also provides the application of the lithium iron phosphate prepared by the preparation method of the lithium iron phosphate in preparing the anode of the lithium ion battery, the process flow is simplified, the preparation cost is saved, and the compacted density and specific capacity of the prepared anode of the lithium ion battery are high.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings that are needed in the description of the embodiments or the prior art will be briefly described, and it is obvious that the drawings in the description below are some embodiments of the present invention, and other drawings can be obtained according to the drawings without inventive effort for a person skilled in the art.
Fig. 1 is an SEM image of lithium iron phosphate provided in example 1 of the present invention;
fig. 2 is an SEM image of lithium iron phosphate provided in example 2 of the present invention;
fig. 3 is an SEM image of lithium iron phosphate provided in example 3 of the present invention;
fig. 4 is an SEM image of lithium iron phosphate provided in example 4 of the present invention;
FIG. 5 is an SEM image of lithium iron phosphate according to example 5 of the present invention;
FIG. 6 is another SEM image of lithium iron phosphate according to example 5 of the present invention;
fig. 7 is an SEM image of lithium iron phosphate provided in comparative example 1 of the present invention.
Detailed Description
The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings and detailed description, but it will be understood by those skilled in the art that the examples described below are some, but not all, examples of the present invention, and are intended to be illustrative of the present invention only and should not be construed as limiting the scope of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention. The specific conditions are not noted in the examples and are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or apparatus used were conventional products commercially available without the manufacturer's attention.
Example 1
The preparation method of the lithium iron phosphate provided by the embodiment comprises the following steps:
(1) Dissolving and reducing (iron powder is used in the reduction process and the pH value of the solution is kept to be 3.5) a titanium white byproduct ferrous sulfate heptahydrate crystal, filtering and clarifying to obtain a pure ferrous sulfate solution with the mass concentration of 250 g/L; simultaneously, ammonium dihydrogen phosphate is dissolved in a certain amount of pure water, ammonia water is added to adjust the pH value of the solution to 7.2, and phosphate solution with 10 percent of phosphorus content is prepared.
(2) And respectively heating the ferrous sulfate solution and the phosphate solution with water to prepare certain concentrations, maintaining the temperature of the two solutions at 45 ℃, keeping the mole ratio of iron to phosphorus at 0.97, synchronously adding the two solutions into a closed reactor for synthesis, reacting for 60min, then entering a reaction kettle for continuous aging, and under the stirring condition, raising the temperature to 90 ℃ by steam, and continuing the reaction for 2h to obtain a reaction material.
(3) Filtering the reaction material by a filter press to obtain a filter cake, continuously adding pure water into the filter press containing the filter cake for washing, wherein the pH value of a washing end point is=3.5, the conductivity is less than or equal to 300us, flash drying the filter cake after washing, calcining the filter cake by a rotary furnace (the calcining temperature is 600 ℃ for 2 hours), crushing, screening and removing iron to obtain SSA=8.9m 2 Anhydrous iron phosphate and ferric oxide mixture with particle size d50=4.2 μm.
(4) Mixing the mixture obtained in the step (3) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, wherein the molar ratio of each element in the mixed slurry is P, fe, li and C=1.0:1.0:1.00:0.40, adding a small amount of industrial phosphoric acid, adjusting the pH of the mixed slurry to 8, carrying out coarse and fine grinding for 5h to obtain nano mixed slurry (D50 is less than or equal to 0.4 mu m), conveying the nano mixed slurry into centrifugal spray drying equipment (the air inlet temperature of spray drying is 200 ℃ and the air outlet temperature is 85 ℃), and rapidly dehydrating to obtain mixed powder material D50=10 mu m with good fluidity and uniform particles.
(5) And (3) in a kiln with nitrogen protective atmosphere, roasting the mixed powder material obtained in the step (4) at 700 ℃, roasting for 12 hours at a temperature, crushing to D50=1.1 mu m, and performing back-end treatment such as batch mixing, dry powder iron removal, packaging and the like to obtain lithium iron phosphate.
SEM examination of lithium iron phosphate prepared in example 1, the examination results are shown in FIG. 1.
As can be seen from FIG. 1, the lithium iron phosphate positive electrode material prepared by the method has the advantages of uniform particles, reasonable collocation of the large and small spheres, small porosity, primary particle size of about 0.3-0.5 mu m, uniform coating of a carbon layer, high compaction density and excellent electrical property.
Example 2
The preparation method of the lithium iron phosphate provided by the embodiment comprises the following steps:
(1) Dissolving and reducing (iron powder is used in the reduction process and the pH value of the solution is kept to be 3.5) a titanium white byproduct ferrous sulfate heptahydrate crystal, filtering and clarifying to obtain a pure ferrous sulfate solution with the mass concentration of 280 g/L; simultaneously, diammonium hydrogen phosphate is dissolved in a certain amount of pure water, ammonia water is added to adjust the pH value of the solution to 8.8, and phosphate solution with the phosphorus content of 8% is prepared.
(2) And respectively heating the ferrous sulfate solution and the phosphate solution with water to prepare certain concentrations, maintaining the temperature of the two solutions at 55 ℃, keeping the mole ratio of iron to phosphorus at 0.98, synchronously adding the two solutions into a closed reactor for synthesis, reacting for 80min, then entering a reaction kettle for continuous aging, and under the stirring condition, raising the temperature to 95 ℃ by steam, and continuing the reaction for 4h to obtain a reaction material.
(3) Filtering the reaction material by a filter press to obtain a filter cake, continuously adding pure water into the filter press containing the filter cake for washing, wherein the pH value of a washing end point is=3.5, the conductivity is less than or equal to 300us, flash drying the filter cake after washing, calcining the filter cake by a rotary furnace (the calcining temperature is 580 ℃ for 2.5 h), crushing, screening and removing iron to obtain SSA=8.9m 2 Per g, anhydrous iron phosphate and iron sesquioxide mixture with particle size d50=4.3 μm.
(4) Mixing the mixture obtained in the step (3) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, wherein the molar ratio of each element in the mixed slurry is P to Fe to Li to C=1.0 to 0.98 to 1.05 to 0.40, adding a small amount of industrial phosphoric acid, adjusting the pH of the mixed slurry to 9, and carrying out coarse grinding and fine grinding for 5 hours to obtain the nano-grade materialThe mixed slurry of the level (D50 is less than or equal to 0.4 mu m) is conveyed into centrifugal spray drying equipment (the air inlet temperature of spray drying is 250 ℃ and the air outlet temperature is 90 ℃), and the mixed powder material D50=20 mu m with good fluidity and uniform particles is obtained.
(5) And (3) in a kiln with argon protective atmosphere, roasting the mixed powder material obtained in the step (4) at 700 ℃, roasting for 6 hours at a temperature, crushing to D50=1.3 mu m, and performing back-end treatment such as batch mixing, dry powder iron removal, packaging and the like to obtain lithium iron phosphate.
XRD detection was performed on the lithium iron phosphate prepared in example 2, and the detection results are shown in FIG. 2.
As can be seen from fig. 2, the primary particle size of the lithium iron phosphate positive electrode material prepared by the method is about 0.2-0.5 μm, carbon is uniformly coated on the surfaces of the lithium iron phosphate particles, and the lithium iron phosphate positive electrode material prepared by the method has high compaction density and excellent electrical property.
Example 3
The preparation method of the lithium iron phosphate provided by the embodiment comprises the following steps:
(1) Dissolving and reducing (iron powder is used in the reduction process and the pH=4 of the solution is maintained) a titanium white byproduct ferrous sulfate heptahydrate crystal, filtering and clarifying to obtain a pure ferrous sulfate solution with the mass concentration of 310g/L; simultaneously, ammonium phosphate is dissolved in a certain amount of pure water, ammonia water is added to adjust the pH value of the solution to 8.0, and phosphate solution with the phosphorus content of 12% is prepared.
(2) And respectively heating the ferrous sulfate solution and the phosphate solution to prepare certain concentrations by water, maintaining the temperature of the two solutions to be 48 ℃, and synchronously adding the two solutions to a closed reactor for synthesis, reacting for 70min, then continuously aging in a reaction kettle, and under the stirring condition, raising the temperature to 98 ℃ by steam, and continuously reacting for 2.5h to obtain a reaction material.
(3) Filtering the reaction material by a filter press to obtain a filter cake, continuously adding pure water into the filter press containing the filter cake for washing, wherein the pH value of a washing end point is=3.3, the conductivity is less than or equal to 300us, and flash evaporating the filter cake after washing is finishedAfter drying, calcination in a rotary kiln (calcination temperature 550 ℃ C., time 3 h), crushing, sieving and iron removal gave SSA=9.3 m 2 Anhydrous iron phosphate and ferric oxide mixture with particle size d50=4.2 μm.
(4) Mixing the mixture obtained in the step (3) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, wherein the molar ratio of each element in the mixed slurry is P, fe, li and C=1.0:0.98:1.00:0.50, adding a small amount of industrial phosphoric acid, adjusting the pH of the mixed slurry to 10, carrying out coarse and fine grinding for 5h to obtain nano mixed slurry (D50 is less than or equal to 0.4 mu m), conveying the nano mixed slurry into centrifugal spray drying equipment (the air inlet temperature of spray drying is 220 ℃ and the air outlet temperature is 87 ℃), and rapidly dehydrating to obtain mixed powder material D50=28 mu m with good fluidity and uniform particles.
(5) And (3) in a kiln with nitrogen protective atmosphere, roasting the mixed powder material obtained in the step (4) at 700 ℃, roasting for 8 hours at a temperature, crushing to D50=1.4 mu m, and performing back-end treatment such as batch mixing, dry powder iron removal, packaging and the like to obtain lithium iron phosphate.
XRD detection was performed on the lithium iron phosphate prepared in example 3, and the detection results are shown in FIG. 3.
As can be seen from fig. 3, the lithium iron phosphate positive electrode material prepared by the method has different sizes, but the size balls are reasonably matched, the porosity is low, the compacted density of the lithium iron phosphate positive electrode material prepared by the method is high, and the electrical property is excellent.
Example 4
The preparation method of the lithium iron phosphate provided by the embodiment comprises the following steps:
(1) Dissolving and reducing (in the reduction process, low carbon steel is used and the pH value of the solution is kept=3.8), filtering and clarifying the titanium white byproduct ferrous sulfate crystal to obtain pure ferrous sulfate solution with the mass concentration of 275 g/L; simultaneously, ammonium dihydrogen phosphate is dissolved in a certain amount of pure water, ammonia water is added to adjust the pH value of the solution to 7.5, and phosphate solution with 9 percent of phosphorus content is prepared.
(2) And respectively heating the ferrous sulfate solution and the phosphate solution with water to prepare certain concentrations, maintaining the temperature of the two solutions at 50 ℃, keeping the mole ratio of iron to phosphorus at 0.99, synchronously adding the two solutions into a closed reactor for synthesis, reacting for 65min, then entering a reaction kettle for continuous aging, and under the stirring condition, raising the temperature to 93 ℃ by steam, and continuing the reaction for 3.5h to obtain a reaction material.
(3) Filtering the reaction material by a filter press to obtain a filter cake, continuously adding pure water into the filter press containing the filter cake for washing, wherein the pH value of a washing end point is=3.8, the conductivity is less than or equal to 300us, flash drying the filter cake after washing, calcining the filter cake by a rotary furnace (the calcining temperature is 570 ℃ for 2 hours), crushing, screening and removing iron to obtain SSA=8.9m 2 Per g, anhydrous iron phosphate and iron sesquioxide mixture with particle size d50=4.6 μm.
(4) Mixing the mixture obtained in the step (3) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, wherein the molar ratio of each element in the mixed slurry is P, fe, li and C=1.0:0.98:1.03:0.45, adding a small amount of industrial phosphoric acid, adjusting the pH of the mixed slurry to 8.5, carrying out coarse and fine grinding for 5h to obtain nano-scale mixed slurry (D50 is less than or equal to 0.4 mu m), conveying the nano-scale mixed slurry into centrifugal spray drying equipment (the air inlet temperature of spray drying is 230 ℃ and the air outlet temperature is 88 ℃), and rapidly dehydrating to obtain mixed powder material D50=15 mu m with good fluidity and uniform particles.
(5) And (3) in a kiln with nitrogen protective atmosphere, roasting the mixed powder material obtained in the step (4) at 700 ℃, roasting for 10 hours at a temperature, crushing to D50=1.6 mu m, and performing back-end treatment such as batch mixing, dry powder iron removal, packaging and the like to obtain lithium iron phosphate.
XRD detection was performed on the lithium iron phosphate prepared in example 4, and the detection results are shown in FIG. 4.
As can be seen from FIG. 4, the size of the lithium iron phosphate positive electrode material prepared by the method is 200nm-400nm, carbon is uniformly coated on the surface of the lithium iron phosphate, and the lithium iron phosphate positive electrode material prepared by the method has high compaction density and excellent electrical property.
Example 5
The preparation method of the lithium iron phosphate provided by the embodiment comprises the following steps:
(1) Dissolving and reducing (iron powder is used in the reduction process and the pH value of the solution is kept to be 3.6) a titanium white byproduct ferrous sulfate heptahydrate crystal, filtering and clarifying to obtain a pure ferrous sulfate solution with the mass concentration of 290 g/L; simultaneously, ammonium dihydrogen phosphate is dissolved in a certain amount of pure water, ammonia water is added to adjust the pH value of the solution to 8.3, and phosphate solution with 11 percent of phosphorus content is prepared.
(2) And respectively heating the ferrous sulfate solution and the phosphate solution with water to prepare certain concentrations, maintaining the temperature of the two solutions at 53 ℃, enabling the molar ratio of iron to phosphorus to be 0.97, synchronously adding the two solutions into a closed reactor for synthesis, reacting for 75min, then entering a reaction kettle for continuous aging, and under the stirring condition, raising the temperature to 96 ℃ by steam, and continuing the reaction for 3h to obtain a reaction material.
(3) Filtering the reaction material by a filter press to obtain a filter cake, continuously adding pure water into the filter press containing the filter cake for washing, wherein the pH value of a washing end point is=3.6, the conductivity is less than or equal to 300us, flash drying the filter cake after washing, calcining the filter cake by a rotary furnace (the calcining temperature is 590 ℃ for 3 hours), crushing, screening and removing iron to obtain SSA=9.1m 2 Anhydrous iron phosphate and ferric oxide mixture with particle size d50=4.1 μm.
(4) Mixing the mixture obtained in the step (3) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, wherein the molar ratio of each element in the mixed slurry is P, fe, li and C=1.0:0.97:1.05:0.50, adding a small amount of industrial phosphoric acid, adjusting the pH of the mixed slurry to 9.2, carrying out coarse and fine grinding for 5h to obtain nano-scale mixed slurry (D50 is less than or equal to 0.4 mu m), conveying the nano-scale mixed slurry into centrifugal spray drying equipment (the air inlet temperature of spray drying is 240 ℃ and the air outlet temperature is 89 ℃), and rapidly dehydrating to obtain mixed powder material D50=23 mu m with good fluidity and uniform particles.
(5) And (3) in a kiln with nitrogen protective atmosphere, roasting the mixed powder material obtained in the step (4) at 700 ℃, roasting for 9 hours at a temperature, crushing to D50=1.5 mu m, and performing back-end treatment such as batch mixing, dry powder iron removal, packaging and the like to obtain lithium iron phosphate.
XRD detection was performed on the lithium iron phosphate prepared in example 5, and the detection results are shown in FIG. 5.
As can be seen from FIG. 5, the lithium iron phosphate positive electrode material prepared by the method has the size of 200nm-500nm, lower porosity, high compacted density and excellent electrical property.
Comparative example 1
The preparation method of lithium iron phosphate provided in this comparative example is substantially the same as that of example 5, except that in step (2), hydrogen peroxide is added simultaneously with the phosphate solution. Wherein the mass fraction of the hydrogen peroxide is 20%, and in the reaction process, fe and H 2 O 2 The molar ratio of (2) to (1) to (2).
Test example 1
The physical and chemical parameters of the lithium iron phosphate prepared in each of the above examples and comparative examples were measured, and the results are shown in table 1 below.
TABLE 1 physicochemical parameter test results of examples 1-5 and comparative example 1 lithium iron phosphate
As can be seen from Table 1, the lithium iron phosphate prepared by the invention has the advantages of high tap density, high specific capacity for first discharge and high first efficiency, while the lithium iron phosphate prepared by comparative example 1 has the advantages of lower tap density, low specific capacity for first discharge and low first efficiency.
Test example 2
SEM examination of lithium iron phosphate prepared in example 5 and comparative example 1 was conducted, and the examination results are shown in FIGS. 6 and 7. As can be seen from fig. 6, the lithium iron phosphate prepared in example 5 of the present invention has good dispersibility and uniform particle size distribution. As can be seen from fig. 7, the lithium iron phosphate prepared in comparative example 1 has poor dispersibility and relatively non-uniform particle size distribution.
While the invention has been illustrated and described with reference to specific embodiments, it is to be understood that the above embodiments are merely illustrative of the technical aspects of the invention and not restrictive thereof; those of ordinary skill in the art will appreciate that: modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some or all of the technical features thereof, without departing from the spirit and scope of the present invention; such modifications and substitutions do not depart from the spirit of the corresponding technical solutions; it is therefore intended to cover in the appended claims all such alternatives and modifications as fall within the scope of the invention.
Claims (16)
1. The preparation method of the lithium iron phosphate is characterized by comprising the following steps of:
(a) Mixing a ferrous sulfate solution with a phosphate solution and carrying out a synthesis reaction to synthesize ferrous phosphate, wherein ferrous ions are not required to be oxidized during the synthesis reaction, aging the solution after the synthesis reaction, carrying out solid-liquid separation on the aged solution, washing a filter cake, drying, calcining, crushing, screening and removing iron to obtain an anhydrous ferric phosphate and ferric oxide mixture;
in the step (a), the ferrous sulfate solution is prepared by dissolving, reducing, filtering and clarifying titanium white byproduct ferrous sulfate heptahydrate crystals; the concentration of the ferrous sulfate solution is 250-310g/L;
in step (a), the phosphate salt comprises ammonium phosphate; the pH of the phosphate solution=7.0-9.0;
in the step (a), during the synthesis reaction, the molar ratio of iron to phosphorus in the reaction solution system is 0.97-1.0; the temperature of the reaction solution system is 45-49 ℃;
(b) Mixing the mixture obtained in step (a) with Li 3 PO 4 、H 3 PO 4 Sequentially adding glucose solution to obtain mixed slurry, grinding the mixed slurry to obtain nano-scale mixed slurry, and drying the nano-scale mixed slurry to obtain mixed powder material;
(c) And (c) roasting the mixed powder material obtained in the step (b) at 700-800 ℃ and crushing to obtain lithium iron phosphate.
2. The method for producing lithium iron phosphate according to claim 1, wherein iron powder or mild steel is used during the reduction and the pH of the solution is maintained at 3.5-4.5.
3. The method for preparing lithium iron phosphate according to claim 1, wherein the mass concentration of phosphorus in the phosphate solution is 8% -12%.
4. The method of producing lithium iron phosphate according to claim 1, wherein in the step (a), the synthesis reaction is performed for 60 to 80 minutes.
5. The method of preparing lithium iron phosphate according to claim 1, wherein in step (a), the temperature of the solution system is 90-98 ℃ during the aging; heating the solution system by steam;
the aging time is 2-4h.
6. The method of producing lithium iron phosphate according to claim 1, wherein in step (a), the drying is flash drying.
7. The method for producing lithium iron phosphate according to claim 1, wherein in step (a), the washed cake is washed with pure water at a washing end point ph=3.3±0.5.
8. The method of producing lithium iron phosphate according to claim 1, wherein in step (a), the calcination is performed at 550 to 600 ℃ for 2 to 3 hours.
9. The method of producing lithium iron phosphate according to claim 1, wherein in step (a), the specific surface area ssa=8.0 to 10.0m of the anhydrous iron phosphate and ferric oxide mixture 2 /g, particle size d50=3-5 μm.
10. The method for producing lithium iron phosphate according to claim 1, wherein in the step (b), the molar ratio of each element in the mixed slurry is P: fe: li: c=1.0, (0.97-1.00): (1.00-1.05): (0.40-0.50);
the pH of the mixed slurry=8.0-10.0.
11. The method of producing lithium iron phosphate according to claim 1, wherein in the step (b), the particle size of the nano-sized mixed slurry is d50.ltoreq.0.4 μm.
12. The method of producing lithium iron phosphate according to claim 1, wherein in step (b), the particle size d50=10 to 30 μm of the mixed powder material.
13. The method of claim 1, wherein in step (b), the drying is spray drying, and the spray drying has an inlet air temperature of 200-250 ℃ and an outlet air temperature of 85-90 ℃.
14. The method for preparing lithium iron phosphate according to claim 1, wherein in the step (c), the time of the heat-retaining calcination is 6 to 12 hours;
the heat preservation roasting process is carried out in a protective atmosphere; the protective atmosphere comprises at least one of nitrogen, argon and helium.
15. The method of producing lithium iron phosphate according to claim 1, wherein in step (c), the particle size d50= (1.1±0.5) μm of the lithium iron phosphate.
16. Use of lithium iron phosphate prepared by the method for preparing lithium iron phosphate according to any one of claims 1-15 in the preparation of a positive electrode of a lithium ion battery.
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