CN117208876A - Preparation method of lithium iron phosphate agglomerate positive electrode material with high mechanical strength and high density - Google Patents
Preparation method of lithium iron phosphate agglomerate positive electrode material with high mechanical strength and high density Download PDFInfo
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- CN117208876A CN117208876A CN202311045075.7A CN202311045075A CN117208876A CN 117208876 A CN117208876 A CN 117208876A CN 202311045075 A CN202311045075 A CN 202311045075A CN 117208876 A CN117208876 A CN 117208876A
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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 40
- 238000002360 preparation method Methods 0.000 title claims abstract description 12
- 239000007774 positive electrode material Substances 0.000 title claims abstract description 11
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims abstract description 58
- 229910052799 carbon Inorganic materials 0.000 claims abstract description 58
- WBJZTOZJJYAKHQ-UHFFFAOYSA-K iron(3+) phosphate Chemical compound [Fe+3].[O-]P([O-])([O-])=O WBJZTOZJJYAKHQ-UHFFFAOYSA-K 0.000 claims abstract description 38
- 239000002245 particle Substances 0.000 claims abstract description 36
- 238000000227 grinding Methods 0.000 claims abstract description 33
- 238000000034 method Methods 0.000 claims abstract description 25
- 230000008569 process Effects 0.000 claims abstract description 15
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims abstract description 13
- 229910052744 lithium Inorganic materials 0.000 claims abstract description 13
- 229910000398 iron phosphate Inorganic materials 0.000 claims abstract description 6
- 238000010438 heat treatment Methods 0.000 claims description 40
- 239000005955 Ferric phosphate Substances 0.000 claims description 32
- 229940032958 ferric phosphate Drugs 0.000 claims description 32
- 229910000399 iron(III) phosphate Inorganic materials 0.000 claims description 32
- 239000007921 spray Substances 0.000 claims description 15
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims description 13
- 229910052808 lithium carbonate Inorganic materials 0.000 claims description 13
- 239000002002 slurry Substances 0.000 claims description 13
- 238000001694 spray drying Methods 0.000 claims description 10
- 238000001816 cooling Methods 0.000 claims description 8
- 239000000843 powder Substances 0.000 claims description 8
- 239000012530 fluid Substances 0.000 claims description 7
- 238000012216 screening Methods 0.000 claims description 7
- 238000003756 stirring Methods 0.000 claims description 7
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 7
- WMFOQBRAJBCJND-UHFFFAOYSA-M Lithium hydroxide Chemical compound [Li+].[OH-] WMFOQBRAJBCJND-UHFFFAOYSA-M 0.000 claims description 6
- 239000004372 Polyvinyl alcohol Substances 0.000 claims description 5
- 229920002451 polyvinyl alcohol Polymers 0.000 claims description 5
- 238000005245 sintering Methods 0.000 claims description 5
- 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 4
- 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 4
- 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 4
- 239000008103 glucose Substances 0.000 claims description 4
- 239000001267 polyvinylpyrrolidone Substances 0.000 claims description 4
- 229920000036 polyvinylpyrrolidone Polymers 0.000 claims description 4
- 235000013855 polyvinylpyrrolidone Nutrition 0.000 claims description 4
- 239000002202 Polyethylene glycol Substances 0.000 claims description 3
- 239000010426 asphalt Substances 0.000 claims description 3
- 229920001223 polyethylene glycol Polymers 0.000 claims description 3
- KXGFMDJXCMQABM-UHFFFAOYSA-N 2-methoxy-6-methylphenol Chemical compound [CH]OC1=CC=CC([CH])=C1O KXGFMDJXCMQABM-UHFFFAOYSA-N 0.000 claims description 2
- 229920002472 Starch Polymers 0.000 claims description 2
- 229930006000 Sucrose Natural products 0.000 claims description 2
- DPXJVFZANSGRMM-UHFFFAOYSA-N acetic acid;2,3,4,5,6-pentahydroxyhexanal;sodium Chemical compound [Na].CC(O)=O.OCC(O)C(O)C(O)C(O)C=O DPXJVFZANSGRMM-UHFFFAOYSA-N 0.000 claims description 2
- YHWCPXVTRSHPNY-UHFFFAOYSA-N butan-1-olate;titanium(4+) Chemical compound [Ti+4].CCCC[O-].CCCC[O-].CCCC[O-].CCCC[O-] YHWCPXVTRSHPNY-UHFFFAOYSA-N 0.000 claims description 2
- 239000001768 carboxy methyl cellulose Substances 0.000 claims description 2
- 239000001913 cellulose Substances 0.000 claims description 2
- 229920002678 cellulose Polymers 0.000 claims description 2
- 235000010980 cellulose Nutrition 0.000 claims description 2
- REKWWOFUJAJBCL-UHFFFAOYSA-L dilithium;hydrogen phosphate Chemical compound [Li+].[Li+].OP([O-])([O-])=O REKWWOFUJAJBCL-UHFFFAOYSA-L 0.000 claims description 2
- 229910001386 lithium phosphate Inorganic materials 0.000 claims description 2
- SNKMVYBWZDHJHE-UHFFFAOYSA-M lithium;dihydrogen phosphate Chemical compound [Li+].OP(O)([O-])=O SNKMVYBWZDHJHE-UHFFFAOYSA-M 0.000 claims description 2
- 230000002572 peristaltic effect Effects 0.000 claims description 2
- 239000005011 phenolic resin Substances 0.000 claims description 2
- 229920001568 phenolic resin Polymers 0.000 claims description 2
- 235000019422 polyvinyl alcohol Nutrition 0.000 claims description 2
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 claims description 2
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 claims description 2
- 239000007787 solid Substances 0.000 claims description 2
- 239000008107 starch Substances 0.000 claims description 2
- 235000019698 starch Nutrition 0.000 claims description 2
- 239000005720 sucrose Substances 0.000 claims description 2
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 claims description 2
- 230000003993 interaction Effects 0.000 abstract description 8
- 239000000126 substance Substances 0.000 abstract description 7
- 239000002131 composite material Substances 0.000 abstract description 6
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 abstract description 5
- 229910001416 lithium ion Inorganic materials 0.000 abstract description 5
- 239000000463 material Substances 0.000 description 17
- 238000005303 weighing Methods 0.000 description 11
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 10
- 239000004576 sand Substances 0.000 description 10
- 238000001035 drying Methods 0.000 description 7
- 239000011164 primary particle Substances 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 6
- 239000007789 gas Substances 0.000 description 6
- 238000002156 mixing Methods 0.000 description 6
- 238000006243 chemical reaction Methods 0.000 description 5
- 239000010410 layer Substances 0.000 description 5
- 229910052757 nitrogen Inorganic materials 0.000 description 5
- 238000013102 re-test Methods 0.000 description 5
- 239000002904 solvent Substances 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 4
- 229910010707 LiFePO 4 Inorganic materials 0.000 description 4
- 238000001878 scanning electron micrograph Methods 0.000 description 4
- 239000000243 solution Substances 0.000 description 4
- 238000005411 Van der Waals force Methods 0.000 description 3
- 238000005056 compaction Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 3
- 239000007772 electrode material Substances 0.000 description 3
- 238000005516 engineering process Methods 0.000 description 3
- 238000005469 granulation Methods 0.000 description 3
- 230000003179 granulation Effects 0.000 description 3
- 229910052739 hydrogen Inorganic materials 0.000 description 3
- 239000001257 hydrogen Substances 0.000 description 3
- 239000002243 precursor Substances 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 230000000630 rising effect Effects 0.000 description 3
- 239000011435 rock Substances 0.000 description 3
- 235000000346 sugar Nutrition 0.000 description 3
- 229910010710 LiFePO Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 238000002441 X-ray diffraction Methods 0.000 description 2
- 239000000853 adhesive Substances 0.000 description 2
- 230000001070 adhesive effect Effects 0.000 description 2
- 230000001276 controlling effect Effects 0.000 description 2
- 230000007547 defect Effects 0.000 description 2
- 238000013461 design Methods 0.000 description 2
- 238000007580 dry-mixing Methods 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 230000001681 protective effect Effects 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 239000011163 secondary particle Substances 0.000 description 2
- 229910013733 LiCo Inorganic materials 0.000 description 1
- 229910032387 LiCoO2 Inorganic materials 0.000 description 1
- 229910019142 PO4 Inorganic materials 0.000 description 1
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 239000010405 anode material Substances 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- 239000006229 carbon black Substances 0.000 description 1
- 238000000975 co-precipitation Methods 0.000 description 1
- 239000011247 coating layer Substances 0.000 description 1
- 235000021551 crystal sugar Nutrition 0.000 description 1
- 238000009831 deintercalation 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
- 238000004146 energy storage Methods 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 238000005087 graphitization Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 238000009830 intercalation Methods 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
- 150000002506 iron compounds Chemical class 0.000 description 1
- 150000002642 lithium compounds Chemical class 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- 231100000956 nontoxicity Toxicity 0.000 description 1
- 238000011056 performance test Methods 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 229910052698 phosphorus Inorganic materials 0.000 description 1
- 239000011574 phosphorus Substances 0.000 description 1
- 238000006068 polycondensation reaction Methods 0.000 description 1
- 229920000642 polymer Polymers 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000012545 processing Methods 0.000 description 1
- 238000010791 quenching Methods 0.000 description 1
- 230000000171 quenching effect Effects 0.000 description 1
- 239000012798 spherical particle Substances 0.000 description 1
- 230000002195 synergetic effect Effects 0.000 description 1
- 238000003786 synthesis reaction Methods 0.000 description 1
Abstract
The invention discloses a preparation method of a high-mechanical-strength high-density lithium iron phosphate aggregate positive electrode material, which belongs to the technical field of lithium ion batteries, and utilizes iron phosphate and a lithium source to dope different types of carbon sources in the process of grinding in thickness and fineness precision to form a composite carbon source, so that different interactions are generated between substances in the process of grinding by the composite carbon source, and further the density and mechanical strength of large particles of the lithium iron phosphate aggregate are improved.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and relates to a preparation method of a high-mechanical-strength high-density lithium iron phosphate aggregate large-particle positive electrode material.
Background
Along with the continuous innovation in the technical field of new energy automobiles, particularly the rapid rise of pure electric automobiles, the energy density of lithium ion batteries is urgently required to be further improved so as to meet the requirement of the pure electric automobiles on long endurance mileage, and the energy density of the lithium ion batteries is mainly determined by electrode materials. Therefore, development of a novel electrode material with high energy density, long cycle life and good rate capability is imperative. The positive electrode materials on the market are mainly LiCoO2, liMn2O4 and LiCo x Mn y Ni 1-x-y O 2 And LiFePO 4 Wherein LiFePO 4 The battery has the advantages of stable structure, good safety, ultra-long cycle life, low cost and the like, and is widely applied to power batteries. Along with the LiFePO of people 4 Continuous research in the field of materials, liFePO 4 The potential of the material as a power electrode material is developed, and the material is mainly used in the fields of energy storage, start-stop power supply and the like, thus being suitable for LiFePO 4 The multiplying power performance and the low temperature performance of the material have more strict requirements. In addition, based on the power LiFePO on the current market 4 The defects of poor processability of the material, and the like, the improvement of the processability of the power sample and the mechanical strength of the particles have remarkable effects of improving the low-temperature performance and reducing the impedance, and therefore, people begin to strive to improve LiFePO 4 Is improved in the compressive strength of large particles.
The existing preparation method generally mixes multiple substance sources (such as lithium source, iron source, phosphorus source, carbon source, etc.) directly when preparing the lithium iron phosphate positive electrode material, especially the carbon source, but does not fully utilize the characteristics of different types in the carbon source, which results in the prepared material having mechanical strength and compactnessThe comprehensive properties such as degree are difficult to fully exert. For example, patent application publication No. CN101948102a discloses a preparation method of lithium iron phosphate positive electrode material, firstly, respectively weighing an iron source, a lithium source and a phosphoric acid source, respectively preparing solutions, then mixing the three solutions, heating in an oil bath at 120 ℃ for 2.5 hours until the bottom has dark green precipitation, and then filtering and separating to obtain nanoscale lithium iron phosphate primary particles; and (3) carrying out spray granulation on the primary particles of the lithium iron phosphate, roasting at 800 ℃ for 6.5 hours, and finally cooling the furnace to room temperature to obtain the lithium iron phosphate anode material. Although the nano-scale lithium iron phosphate material with good electrical property and uniform primary particle distribution is prepared by the coprecipitation method, the compaction density of particles is poor, higher energy density cannot be provided, the multiplying power performance is not outstanding, the synthesis process is limited, and large-scale mass production is difficult to realize. In the patent application with the publication number of CN 102173403A, a nanometer-sized precursor material is uniformly dispersed, then is uniformly mixed with a lithium source, a carbon source and a proper amount of adhesive, and then is subjected to a dry mixing granulation process to obtain a spherical micro-nano lithium iron phosphate precursor material with micron-sized secondary particles, and after drying, the spherical micro-nano lithium iron phosphate material is obtained through high-temperature heat treatment. The micro-nano lithium iron phosphate material has the characteristics of high tap density, good processing performance, large specific surface area and multiple holes, but is forced to be subjected to the defects of a dry mixing process, so that the sample uniformity is poor, the low temperature and the low doubling performance are low, the micro-nano lithium iron phosphate material cannot be directly applied as a power type material, and the porous structure also limits the compaction of a pole piece and cannot further improve the energy density. In the patent application with publication number CN 102642820A, a lithium compound, an iron compound, a phosphate, a doped metal compound and carbon black are taken as raw materials, and are added into a ball mill for wet mixing; spray drying and then placing in N 2 Presintering in a roasting furnace as protective gas, adding adhesive polyethylene glycol, wet mixing again, spray drying, and standing in N 2 And (3) performing secondary roasting in a roasting furnace serving as protective gas to obtain the high-density spherical lithium iron phosphate material. In the above patent documents, either no carbon source is used or only a single carbon source is used, and even if a plurality of carbon source selections are involved, it is not recognized that different types of carbon are usedThe different functions of the sources and the promotion function of mutual collocation are achieved, so that how to fully utilize the characteristics of different types in the carbon sources and further improve the comprehensive properties such as mechanical strength, compactness and the like through the collocation design of the carbon sources is an important research subject.
Disclosure of Invention
The invention aims to provide a method for preparing high-mechanical-strength and high-density lithium iron phosphate agglomerate large particles, which utilizes iron phosphate and a lithium source to dope different types of carbon sources in the process of grinding in thickness and fineness precision to form a composite carbon source, so that the composite carbon source generates different interactions among substances in the grinding process, and further the density and mechanical strength of the lithium iron phosphate agglomerate large particles are improved.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
the preparation method of the lithium iron phosphate agglomerate positive electrode material with high mechanical strength and high density comprises the following steps:
uniformly dispersing a first carbon source in water to prepare a primary mixed system, wherein the first carbon source is at least one of polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, cellulose, starch and sodium carboxymethyl cellulose;
adding ferric phosphate, a lithium source and a second type of carbon source into the primary mixed system, and uniformly stirring to prepare a secondary mixed system, wherein the second type of carbon source is at least one of sucrose, glucose, rock candy and active carbon;
coarse grinding is carried out on the secondary mixed system by a coarse grinding mill, and the slurry after coarse grinding is transferred to a fine grinding mill for fine grinding;
and (3) carrying out spray drying on the slurry after fine grinding, carrying out stage heating sintering on the dried powder under the protection of inert atmosphere, and cooling and screening to obtain the lithium iron phosphate aggregate large particles.
Preferably, the molar ratio of lithium source to iron phosphate, li: p=1, (1.0-1.1), preferably 1, (1.0-1.02); the mass of the first carbon source is 1-2% of that of the ferric phosphate, and the mass of the second carbon source is 7-9% of that of the ferric phosphate.
Preferably, the solid content of the iron phosphate after fine grinding is 30% -50%.
Preferably, the lithium source is one or more of lithium phosphate, lithium carbonate, lithium hydroxide, dilithium phosphate, and lithium dihydrogen phosphate.
Preferably, a third carbon source is added into the slurry after fine grinding, uniformly stirred and then spray-dried, wherein the third carbon source is at least one of phenolic resin, asphalt and tetrabutyl titanate, and the mass of the third carbon source is 1-2% of that of the ferric phosphate.
Preferably, the particle size of coarse grinding is controlled to 700-800 nm, and the particle size of fine grinding is controlled to 200-220 nm.
Preferably, the spray dryer selected for spray drying is a centrifugal dryer, a pressure dryer, a fluid dryer or other type of special dryer.
Preferably, the gas pressure of spray drying is 0.3-0.6 MPa, and the feeding frequency of peristaltic pump is 0-60 Hz.
Preferably, the air inlet temperature of spray drying is 200-280 ℃, and the air outlet temperature is 60-110 ℃; the median diameter D50 of the spray is 6-12 μm.
Preferably, the temperature rising sintering condition is that the temperature rising is carried out at the temperature rising rate of 1-10 ℃/min, the temperature is raised to 200-350 ℃ from the room temperature, and the temperature is kept for 1-5h; heating to 400-500 ℃, and preserving heat for 3-7h; and then continuously heating to 700-800 ℃, and preserving heat for 5-15h.
Compared with the prior art, the invention has the following advantages:
1. the composite carbon source enhances interaction: the invention carries out collocation design on different types of carbon sources, utilizes the physical and chemical properties of the carbon sources to divide the carbon sources into two types and three types, and the interaction force of the first type of carbon source comprises hydrogen bond and Van der Waals force, and in the continuous contact process of ferric phosphate and lithium source in the grinding process, the hydrogen bond and Van der Waals force of the carbon source are utilized to continuously form strong interaction force (hydrogen bond and Van der Waals force) on the surfaces of the raw materials; the interaction force of the second type of carbon source comprises covalent bonds or ionic bonds, and in the grinding process, the special carbon source is continuously contacted with lithium carbonate on the surface of ferric phosphate to form local covalent bonds and ionic bonds, substances are tightly combined by strong interaction force, and after primary particles are tightly wrapped with carbon, the particles are also connected with each other to form a high-density aggregate; the third carbon source is added before drying after fine grinding, the carbon layer formed by the third carbon source is coated on the particle surface in the spray drying process, the door closing effect formed by polycondensation reaction after heating is mainly utilized, a compact rigid coating layer is formed on the surface of the secondary particle after fine grinding, namely a rigid carbon film is formed on a diffusion layer, the internal primary particles are bound, and the unique micropore structure of the carbon film can ensure the intercalation and deintercalation of lithium ions. The holding of the carbon layer will promote the overall compressive strength and flexibility of the sphere. Therefore, through the synergistic effect between different types of carbon sources, strong interaction force between molecules and between particles can be formed, so that the mechanical strength and the compactness of the sphere material can be greatly improved.
2. An efficient preparation process of the agglomerates comprises the following steps: the invention uses the granulation effect of the drying process to tightly combine and compress the substances into spheres to form spheres with uniform particles, and forms agglomerate precursor particles with highly controllable particle size by regulating and controlling the drying technology; the invention adopts a step-by-step heating sintering process, so that the bond energy of chemical bonds formed continuously during grinding of a carbon layer, a lithium source and ferric phosphate is continuously improved, the connection between primary particles is increased, the graphitization degree of the carbon layer is high through high-temperature quenching, the surface of a sphere is smoother, the whole body is compact and round, the mechanical strength of an aggregate is obviously improved, and the lithium iron phosphate aggregate anode with high mechanical strength is prepared; on the other hand, the invention has the advantages of low cost of raw materials, no toxicity and pollution, higher overall yield, simple preparation process and suitability for mass production.
3. Advanced fluid drying techniques: the invention uses a novel fluid drying technology to dry slurry, and obtains spherical particles with controllable particle size and high sphericity by regulating and controlling the addition amount of special carbon sources and combining the regulation and control of the process parameters of the drying technology. The dried material takes a sphere as a unit, forms an integrated whole under the action of stress, and combines with a unique formula to prepare the lithium iron phosphate aggregate positive electrode material with ultrahigh mechanical strength.
Drawings
Fig. 1 is an SEM image of lithium iron phosphate prepared in example 1 of the present invention.
Fig. 2 is an XRD pattern of lithium iron phosphate prepared in example 1 of the present invention.
FIG. 3 is a plot of the capacity test of lithium iron phosphate prepared in example 1 of the present invention.
Fig. 4 is an SEM image of lithium iron phosphate prepared in comparative example 1 of the present invention.
Detailed Description
The invention is further illustrated by the following examples. These examples are merely illustrative of the present invention and are not intended to limit the scope of applicability of the invention.
Example 1
1) Taking water as a solvent, weighing polyvinyl alcohol accounting for 1% of the mass of the ferric phosphate, and dissolving to obtain a primary mixed system.
2) Weighing lithium carbonate and ferric phosphate according to the molar ratio of Li to P=1:1.012, adding ferric phosphate, stirring and mixing until the color of the mixed solution becomes light, adding lithium carbonate into the mixed system, adding rock sugar accounting for 8.0% of the mass of the ferric phosphate, and uniformly mixing to obtain a secondary mixed system.
3) Crushing the secondary mixed system by using a coarse sand mill, transferring the crushed secondary mixed system into a fine sand mill for fine grinding after the granularity reaches 700-800 nm, and finally, re-testing the granularity to be qualified within the range of 200-220 nm. And adding polymer modified asphalt with the mass of 1.5% of that of ferric phosphate into the system, and uniformly mixing.
4) The slurry is spray dried, a two-fluid dryer is selected as the spray dryer, the gas pressure is 0.45MPa, the inlet temperature is 240 ℃, and the air outlet temperature is 80 ℃.
5) Placing the dried powder into a reaction furnace protected by nitrogen, heating to 280 ℃ at a heating rate of 5 ℃/min, and preserving heat for 3 hours; heating to 460 ℃ at a heating rate of 5 ℃/min, and preserving heat for 5 hours; heating to 750 ℃ at a heating rate of 5 ℃/min, and preserving heat for 8 hours; and then naturally cooling to room temperature, and carrying out subsequent screening treatment to obtain large lithium iron phosphate agglomerate particles.
The particles and properties of the lithium iron phosphate prepared in example 1 were characterized as represented by:
fig. 1 is an SEM image of lithium iron phosphate prepared in example 1. The obtained sample can be clearly observed to have large particles with the particle size of 8-9 mu m, the primary particles are small particles with the particle size of about 220nm or sheet-shaped particles, the small particles are uniformly distributed, and the particle surfaces are compact, so that the whole compressive capacity is improved, the mechanical strength is improved, and the mechanical strength can reach 130MPa.
Fig. 2 is an XRD pattern of lithium iron phosphate prepared in example 1. The diffraction peaks in the figures correspond to the lithium iron phosphate standard peak (JCPDS 19-0721) in PDF cards to an extremely high degree, and no impurity peaks.
FIG. 3 is a graph showing the capacity test of lithium iron phosphate prepared in example 1 of the present invention. From the capacity test results, it can be seen that: the sample 0.1C discharge can reach 155mAh/g.
Example 2
1) Taking water as a solvent, weighing polyvinyl alcohol accounting for 1% of the mass of the ferric phosphate, and dissolving to obtain a primary mixed system.
2) And (3) weighing lithium carbonate and ferric phosphate according to the molar ratio of Li to P=1:1.05, adding ferric phosphate, lithium carbonate and rock sugar accounting for 9% of the mass of the ferric phosphate into a container of the mixed system, and uniformly stirring to obtain a secondary mixed system.
3) Crushing the secondary mixed system by a coarse sand mill, transferring the crushed secondary mixed system into a fine sand mill for fine grinding after the granularity reaches 700-800 nm, and finally, re-testing the granularity to be qualified within the range of 200-220 nm.
4) The slurry is spray dried, a two-fluid dryer is selected as the spray dryer, the gas pressure is 0.45MPa, the inlet temperature is 200 ℃, and the air outlet temperature is 60 ℃.
5) Placing the dried powder into a reaction furnace protected by nitrogen, heating to 350 ℃ at a heating rate of 10 ℃/min, and preserving heat for 1h; heating to 500 ℃ at a heating rate of 10 ℃/min, and preserving heat for 3 hours; then continuously heating to 800 ℃ at the same heating rate, and preserving heat for 5 hours; and then naturally cooling to room temperature, and obtaining large lithium iron phosphate aggregate particles after subsequent screening treatment.
Example 3
1) Taking water as a solvent, weighing polyvinyl alcohol accounting for 1% of the mass of the ferric phosphate, and dissolving to obtain a primary mixed system.
2) Weighing lithium carbonate and ferric phosphate according to the molar ratio of Li to P=1 to 1.1, adding ferric phosphate, lithium carbonate and rock sugar accounting for 8% of the mass of the ferric phosphate into a container added with the mixed system, and uniformly stirring.
3) Crushing the secondary mixed system by a coarse sand mill, transferring the crushed secondary mixed system into a fine sand mill for fine grinding after the granularity reaches 700-800 nm, and finally, re-testing the granularity to be qualified within the range of 200-220 nm.
4) The slurry is spray dried, a laboratory small centrifugal dryer is selected as the spray dryer, the inlet temperature is 280 ℃, and the air outlet temperature is 110 ℃.
5) Placing the dried powder into a reaction furnace protected by nitrogen, heating to 200 ℃ at a heating rate of 1 ℃/min, and preserving heat for 5 hours; then heating to 400 ℃ at a heating rate of 1 ℃/min, and preserving heat for 7 hours; heating to 700 ℃ at a heating rate of 1 ℃/min, and preserving heat for 15h; and then naturally cooling to room temperature, and carrying out subsequent screening treatment to obtain large lithium iron phosphate agglomerate particles.
Example 4
1) Taking water as a solvent, weighing polyvinylpyrrolidone accounting for 2% of the mass of the ferric phosphate, and dissolving to obtain a primary mixed system.
2) And weighing lithium carbonate and ferric phosphate according to the molar ratio of Li to P=1:1.012, adding ferric phosphate, lithium carbonate and glucose accounting for 7.5% of the mass of ferric phosphate into a container of the mixed system, and uniformly stirring to obtain a secondary mixed system.
3) Crushing the secondary mixed system by a coarse sand mill, transferring the crushed material to a fine sand mill for fine grinding after the granularity reaches 700-800 nm, and finally, re-testing the granularity to be qualified within the range of 200-220 nm.
4) The slurry is spray dried, a two-fluid dryer is selected as the spray dryer, the gas pressure is 0.45MPa, the inlet temperature is 240 ℃, and the air outlet temperature is 80 ℃.
5) Placing the dried powder into a reaction furnace protected by nitrogen, heating to 220 ℃ at a heating rate of 5 ℃/min, and preserving heat for 3 hours; heating to 460 ℃ at a heating rate of 5 ℃/min, and preserving heat for 5 hours; heating to 710 ℃ at a heating rate of 5 ℃/min, and preserving heat for 8 hours; and then naturally cooling to room temperature, and carrying out subsequent screening treatment to obtain large lithium iron phosphate agglomerate particles.
Example 5
1) Taking water as a solvent, weighing polyvinylpyrrolidone accounting for 2% of the mass of the ferric phosphate, and dissolving to obtain a primary mixed system.
2) And weighing lithium carbonate and ferric phosphate according to the molar ratio of Li to P=1:1.012, adding ferric phosphate, lithium carbonate and glucose accounting for 7.5% of the mass of ferric phosphate into a container of the mixed system, and uniformly stirring to obtain a secondary mixed system.
3) Crushing the secondary mixed system by a coarse sand mill, transferring the crushed secondary mixed system into a fine sand mill for fine grinding after the granularity reaches 700-800 nm, and finally, re-testing the granularity to be qualified within the range of 200-220 nm.
4) The slurry is spray dried, a pressure dryer is selected for the spray dryer, the feeding pressure is controlled to be 20-30bar, the inlet temperature is 230 ℃, and the air outlet temperature is 80 ℃.
5) Placing the dried powder into a reaction furnace protected by nitrogen, heating to 220 ℃ at a heating rate of 5 ℃/min, and preserving heat for 3 hours; heating to 460 ℃ at a heating rate of 5 ℃/min, and preserving heat for 5 hours; heating to 710 ℃ at a heating rate of 5 ℃/min, and preserving heat for 8 hours; and then naturally cooling to room temperature, and carrying out subsequent screening treatment to obtain large lithium iron phosphate agglomerate particles.
Comparative example 1
Substantially the same conditions and procedures as in example 1 were followed except that only crystal sugar was used as the carbon source.
Fig. 4 is an SEM image of lithium iron phosphate prepared in comparative example 1. It can be clearly observed that the particle sizes of the samples are basically consistent and are all 8-10 mu m, but the fine powder on the particle surfaces is increased, the surface density is reduced, and the particles are loose.
Table 1 example and comparative example preparation of sample performance test results
| Test item | Example 1 | Example 2 | Example 3 | Example 4 | Example 5 | Comparative example 1 |
| Mechanical strength (MPa) | 130 | 86 | 73 | 46 | 54 | 34 |
| First week discharge (mAh/g) | 155.6 | 154.3 | 154.9 | 158.9 | 160.2 | 161.5 |
| 1C discharge (mAh/g) | 138.7 | 136.4 | 135.2 | 138.4 | 140.2 | 139.8 |
| Tap density (g/cm) 3 ) | 1.61 | 1.52 | 1.34 | 1.37 | 1.21 | 1.02 |
| Density of compaction (g/cm) 3 ) | 2.43 | 2.44 | 2.39 | 2.23 | 2.18 | 2.17 |
| D50(μm) | 8.045 | 8.566 | 16.043 | 9.414 | 7.807 | 6.167 |
| D100(μm) | 39.340 | 43.749 | 51.618 | 44.776 | 38.176 | 34.428 |
As can be seen from the test data in table 1, compared with the comparative example, the mechanical strength and the compactness of the prepared lithium iron phosphate positive electrode material sample are higher due to the adoption of different types of composite carbon sources; among them, example 1 was more excellent in mechanical strength and density than the other examples due to the use of three types of carbon sources.
The above embodiments are only for illustrating the technical solution of the present invention and not for limiting the same, and those skilled in the art may modify or substitute the technical solution of the present invention, and the scope of the present invention is defined by the claims.
Claims (10)
1. The preparation method of the lithium iron phosphate agglomerate positive electrode material with high mechanical strength and high density is characterized by comprising the following steps:
uniformly dispersing a first carbon source in water to prepare a primary mixed system, wherein the first carbon source is at least one of polyethylene glycol, polyvinylpyrrolidone, polyvinyl alcohol, cellulose, starch and sodium carboxymethyl cellulose;
adding ferric phosphate, a lithium source and a second type of carbon source into the primary mixed system, and uniformly stirring to prepare a secondary mixed system, wherein the second type of carbon source is at least one of sucrose, glucose, rock candy and active carbon;
coarse grinding is carried out on the secondary mixed system by a coarse grinding mill, and the slurry after coarse grinding is transferred to a fine grinding mill for fine grinding;
and (3) carrying out spray drying on the slurry after fine grinding, carrying out stage heating sintering on the dried powder under the protection of inert atmosphere, and cooling and screening to obtain the lithium iron phosphate aggregate large particles.
2. The process according to claim 1, wherein the molar ratio of lithium source to iron phosphate, li, is p=1, (1.0 to 1.1), preferably 1, (1.0 to 1.02); the mass of the first carbon source is 1-2% of that of the ferric phosphate, and the mass of the second carbon source is 7-9% of that of the ferric phosphate.
3. The method of claim 1, wherein the iron phosphate has a solids content of 30% to 50% after fine grinding.
4. The method of claim 1, wherein the lithium source is one or more of lithium phosphate, lithium carbonate, lithium hydroxide, dilithium phosphate, and lithium dihydrogen phosphate.
5. The method according to claim 1, wherein a third type of carbon source is added to the finely ground slurry, and the slurry is stirred uniformly, and then spray-dried, wherein the third type of carbon source is at least one of phenolic resin, asphalt and tetrabutyl titanate, and the mass of the third type of carbon source is 1% -2% of that of the ferric phosphate.
6. The method of claim 1, wherein the coarse grinding is controlled to a particle size of 700 to 800nm and the fine grinding is controlled to a particle size of 200 to 220nm.
7. The method of claim 1, wherein the spray dryer selected for spray drying is a centrifugal dryer, a pressure dryer, or a fluid dryer.
8. The process according to claim 7, wherein the spray-dried gas pressure is from 0.3 to 0.6MPa and the peristaltic pump feed frequency is from 0 to 60Hz.
9. The preparation method according to claim 7, wherein the air inlet temperature of spray drying is 200-280 ℃ and the air outlet temperature is 60-110 ℃; the median diameter D50 of the spray is 6-12 μm.
10. The method according to claim 1, wherein the conditions for the stage-wise temperature-rising sintering are that the temperature is raised at a temperature-rising rate of 1 to 10 ℃/min, the temperature is raised from room temperature to 200 to 350 ℃, and the temperature is kept for 1 to 5 hours; heating to 400-500 ℃, and preserving heat for 3-7h; and then continuously heating to 700-800 ℃, and preserving heat for 5-15h.
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