CN117842958A - Preparation method and application of lithium pyrophosphate - Google Patents
Preparation method and application of lithium pyrophosphate Download PDFInfo
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- CN117842958A CN117842958A CN202311809528.9A CN202311809528A CN117842958A CN 117842958 A CN117842958 A CN 117842958A CN 202311809528 A CN202311809528 A CN 202311809528A CN 117842958 A CN117842958 A CN 117842958A
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- lithium
- pyrophosphate
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- lithium pyrophosphate
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- MVGWWCXDTHXKTR-UHFFFAOYSA-J tetralithium;phosphonato phosphate Chemical compound [Li+].[Li+].[Li+].[Li+].[O-]P([O-])(=O)OP([O-])([O-])=O MVGWWCXDTHXKTR-UHFFFAOYSA-J 0.000 title claims abstract description 85
- 238000002360 preparation method Methods 0.000 title claims abstract description 15
- 238000001914 filtration Methods 0.000 claims abstract description 36
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims abstract description 35
- 239000000047 product Substances 0.000 claims abstract description 34
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 claims abstract description 26
- 229910052808 lithium carbonate Inorganic materials 0.000 claims abstract description 26
- XPPKVPWEQAFLFU-UHFFFAOYSA-N diphosphoric acid Chemical compound OP(O)(=O)OP(O)(O)=O XPPKVPWEQAFLFU-UHFFFAOYSA-N 0.000 claims abstract description 22
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 21
- 238000006243 chemical reaction Methods 0.000 claims abstract description 20
- 239000003960 organic solvent Substances 0.000 claims abstract description 17
- 238000001035 drying Methods 0.000 claims abstract description 15
- 239000000463 material Substances 0.000 claims abstract description 15
- 229940005657 pyrophosphoric acid Drugs 0.000 claims abstract description 13
- 239000000706 filtrate Substances 0.000 claims abstract description 9
- 239000012265 solid product Substances 0.000 claims abstract description 7
- 239000002002 slurry Substances 0.000 claims abstract description 6
- 238000002156 mixing Methods 0.000 claims abstract description 4
- 238000003756 stirring Methods 0.000 claims description 30
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 claims description 24
- 239000007774 positive electrode material Substances 0.000 claims description 13
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 claims description 8
- 229910052744 lithium Inorganic materials 0.000 claims description 8
- 239000003795 chemical substances by application Substances 0.000 claims description 6
- 239000011248 coating agent Substances 0.000 claims description 6
- 238000000576 coating method Methods 0.000 claims description 6
- GELKBWJHTRAYNV-UHFFFAOYSA-K lithium iron phosphate Chemical compound [Li+].[Fe+2].[O-]P([O-])([O-])=O GELKBWJHTRAYNV-UHFFFAOYSA-K 0.000 claims description 6
- 239000007773 negative electrode material Substances 0.000 claims description 6
- 238000001291 vacuum drying Methods 0.000 claims description 6
- 238000005406 washing Methods 0.000 claims description 6
- 238000001816 cooling Methods 0.000 claims description 5
- 235000011180 diphosphates Nutrition 0.000 claims description 5
- 229940048084 pyrophosphate Drugs 0.000 claims description 5
- 230000001476 alcoholic effect Effects 0.000 claims description 4
- 239000003607 modifier Substances 0.000 claims description 4
- 239000007784 solid electrolyte Substances 0.000 claims description 4
- 239000000853 adhesive Substances 0.000 claims description 2
- 230000001070 adhesive effect Effects 0.000 claims description 2
- 239000006258 conductive agent Substances 0.000 claims description 2
- 230000001502 supplementing effect Effects 0.000 claims description 2
- 238000004519 manufacturing process Methods 0.000 claims 7
- 229910001386 lithium phosphate Inorganic materials 0.000 abstract description 10
- TWQULNDIKKJZPH-UHFFFAOYSA-K trilithium;phosphate Chemical compound [Li+].[Li+].[Li+].[O-]P([O-])([O-])=O TWQULNDIKKJZPH-UHFFFAOYSA-K 0.000 abstract description 10
- 239000006227 byproduct Substances 0.000 abstract description 7
- 239000002245 particle Substances 0.000 abstract description 5
- 239000000243 solution Substances 0.000 description 17
- 235000019441 ethanol Nutrition 0.000 description 11
- 239000007788 liquid Substances 0.000 description 8
- 238000000034 method Methods 0.000 description 7
- 230000000052 comparative effect Effects 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- HBBGRARXTFLTSG-UHFFFAOYSA-N Lithium ion Chemical compound [Li+] HBBGRARXTFLTSG-UHFFFAOYSA-N 0.000 description 4
- 229910001416 lithium ion Inorganic materials 0.000 description 4
- 239000002994 raw material Substances 0.000 description 4
- OAICVXFJPJFONN-UHFFFAOYSA-N Phosphorus Chemical compound [P] OAICVXFJPJFONN-UHFFFAOYSA-N 0.000 description 3
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 3
- 238000002425 crystallisation Methods 0.000 description 3
- 230000008025 crystallization Effects 0.000 description 3
- SNKMVYBWZDHJHE-UHFFFAOYSA-M lithium;dihydrogen phosphate Chemical compound [Li+].OP(O)([O-])=O SNKMVYBWZDHJHE-UHFFFAOYSA-M 0.000 description 3
- 229910052698 phosphorus Inorganic materials 0.000 description 3
- 239000011574 phosphorus Substances 0.000 description 3
- 239000002243 precursor Substances 0.000 description 3
- 239000007787 solid Substances 0.000 description 3
- 239000000126 substance Substances 0.000 description 3
- CURLTUGMZLYLDI-UHFFFAOYSA-N Carbon dioxide Chemical compound O=C=O CURLTUGMZLYLDI-UHFFFAOYSA-N 0.000 description 2
- 229910019142 PO4 Inorganic materials 0.000 description 2
- NBIIXXVUZAFLBC-UHFFFAOYSA-N Phosphoric acid Chemical compound OP(O)(O)=O NBIIXXVUZAFLBC-UHFFFAOYSA-N 0.000 description 2
- 239000007864 aqueous solution Substances 0.000 description 2
- 239000010406 cathode material Substances 0.000 description 2
- 239000011247 coating layer Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000011161 development Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 235000021317 phosphate Nutrition 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 238000004448 titration Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 229910000147 aluminium phosphate Inorganic materials 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 238000003556 assay Methods 0.000 description 1
- 239000012298 atmosphere Substances 0.000 description 1
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 229910052799 carbon Inorganic materials 0.000 description 1
- 239000001569 carbon dioxide Substances 0.000 description 1
- 229910002092 carbon dioxide Inorganic materials 0.000 description 1
- 239000002131 composite material Substances 0.000 description 1
- 239000004020 conductor Substances 0.000 description 1
- 238000009792 diffusion process Methods 0.000 description 1
- 238000005265 energy consumption Methods 0.000 description 1
- 238000001704 evaporation Methods 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 235000013373 food additive Nutrition 0.000 description 1
- 239000002778 food additive Substances 0.000 description 1
- 239000007789 gas Substances 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- 238000006138 lithiation reaction Methods 0.000 description 1
- MRVHOJHOBHYHQL-UHFFFAOYSA-M lithium metaphosphate Chemical compound [Li+].[O-]P(=O)=O MRVHOJHOBHYHQL-UHFFFAOYSA-M 0.000 description 1
- -1 lithium pyrophosphate modified lithium iron phosphate Chemical class 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 238000006386 neutralization reaction Methods 0.000 description 1
- 229910052760 oxygen Inorganic materials 0.000 description 1
- 239000001301 oxygen Substances 0.000 description 1
- NBIIXXVUZAFLBC-UHFFFAOYSA-K phosphate Chemical compound [O-]P([O-])([O-])=O NBIIXXVUZAFLBC-UHFFFAOYSA-K 0.000 description 1
- 239000010452 phosphate Substances 0.000 description 1
- 150000003013 phosphoric acid derivatives Chemical class 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 238000004321 preservation Methods 0.000 description 1
- 238000004537 pulping Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 238000007086 side reaction Methods 0.000 description 1
- FQENQNTWSFEDLI-UHFFFAOYSA-J sodium diphosphate Chemical compound [Na+].[Na+].[Na+].[Na+].[O-]P([O-])(=O)OP([O-])([O-])=O FQENQNTWSFEDLI-UHFFFAOYSA-J 0.000 description 1
- 229940048086 sodium pyrophosphate Drugs 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- 239000002345 surface coating layer Substances 0.000 description 1
- 235000019818 tetrasodium diphosphate Nutrition 0.000 description 1
- 239000001577 tetrasodium phosphonato phosphate Substances 0.000 description 1
- GKGOCHJFNRQDIA-UHFFFAOYSA-K trilithium [hydroxy(oxido)phosphoryl] phosphate Chemical compound [Li+].[Li+].[Li+].OP([O-])(=O)OP([O-])([O-])=O GKGOCHJFNRQDIA-UHFFFAOYSA-K 0.000 description 1
- RZLVQBNCHSJZPX-UHFFFAOYSA-L zinc sulfate heptahydrate Chemical compound O.O.O.O.O.O.O.[Zn+2].[O-]S([O-])(=O)=O RZLVQBNCHSJZPX-UHFFFAOYSA-L 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- 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
- C01B25/38—Condensed phosphates
- C01B25/42—Pyrophosphates
- C01B25/425—Pyrophosphates of alkali metals
-
- 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
-
- 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
- H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
- H01M10/0561—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of inorganic materials only
- H01M10/0562—Solid materials
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- 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
- H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
- H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/36—Selection of substances as active materials, active masses, active liquids
- H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
- H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/621—Binders
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/02—Electrodes composed of, or comprising, active material
- H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
- H01M4/624—Electric conductive fillers
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- C—CHEMISTRY; METALLURGY
- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2004/00—Particle morphology
- C01P2004/60—Particles characterised by their size
- C01P2004/61—Micrometer sized, i.e. from 1-100 micrometer
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- C01—INORGANIC CHEMISTRY
- C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
- C01P2006/00—Physical properties of inorganic compounds
- C01P2006/80—Compositional purity
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Crystallography & Structural Chemistry (AREA)
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Abstract
The invention relates to the technical field of lithium pyrophosphate preparation, and in particular provides a preparation method and application of lithium pyrophosphate, comprising the following steps: s1, mixing lithium carbonate with water to prepare slurry, then dropwise adding pyrophosphoric acid until the pH reaches 6.5-7.5, and filtering after the reaction is finished; s2, adding an alcohol organic solvent into the filtrate obtained by filtering until lithium pyrophosphate is completely separated out, and then filtering; s3, drying the solid product obtained by filtering in the step S2 to obtain a lithium pyrophosphate product. According to the invention, the lithium pyrophosphate is slowly dripped into the lithium carbonate slurry to react to obtain the lithium pyrophosphate, most of byproducts can be removed by utilizing the fact that the lithium carbonate and the lithium phosphate are insoluble or slightly soluble in water and filtering, and then the lithium pyrophosphate is separated out by utilizing the alcohol organic solvent to obtain a lithium pyrophosphate product with high purity, small particles and uniformity, so that the application of the lithium pyrophosphate product in the field of battery materials is remarkably expanded.
Description
Technical Field
The invention relates to the technical field of lithium pyrophosphate preparation, in particular to a preparation method and application of lithium pyrophosphate.
Background
With the development of new energy automobiles, the requirements of the market on the endurance mileage, the cycle performance and the safety of the lithium power battery are higher and higher, and the positive electrode materials serving as important components of the lithium ion power battery comprise lithium iron phosphate and ternary positive electrode materials, which play a key role in the electrochemical performance, the safety performance, the cost and the like of the whole battery.
Currently, the research on the performance improvement of the cathode material mainly has two directions: 1) Surface coating, namely dispersing a positive electrode material in phosphate aqueous solution, and then drying and calcining at high temperature to form a surface coating layer; 2) Doping, i.e. doping metallic or non-metallic elements in the lattice of the positive electrode material. Among them, the material mainly used in the surface coating study is lithium pyrophosphate, which is a good conductor for lithium ion diffusion. For example, chinese patent CN108511715a discloses a preparation method of ternary material of lithium ion battery coated with lithium pyrophosphate on the surface, wherein the pH of the ternary material raw material solution is adjusted to 11-12 by lithium dihydrogen phosphate, and the precursor is obtained through solid-liquid separation, washing and drying after reaction; the obtained precursor is subjected to heat preservation and annealing at 450-550 ℃ under the oxygen-containing atmosphere to obtain the lithium ion battery ternary material coated with lithium pyrophosphate on the surface, and the patent actually precipitates lithium dihydrogen phosphate on the surface of the ternary positive electrode material in the form of lithium phosphate under the alkaline condition, and then the lithium dihydrogen phosphate is dried and calcined at high temperature to form a lithium pyrophosphate coating layer, but the lithium phosphate has stable property under the alkaline condition and is difficult to dehydrate to form lithium pyrophosphate. In another example, chinese patent CN102244241a discloses a preparation method of lithium pyrophosphate modified lithium iron phosphate composite material, in which lithium pyrophosphate is used as a coating layer to modify a positive electrode material, specifically, a lithium iron phosphate precursor, a phosphorus source, a lithium source and an organic carbon source are ball-milled and mixed uniformly in a liquid system, and then dried and calcined at a high temperature to form a lithium iron phosphate coated lithium iron phosphate positive electrode material, wherein uneven distribution of the phosphorus source and the lithium source may occur in the process, resulting in side reaction.
In view of the role of lithium pyrophosphate in modification of cathode materials and the fact that lithium pyrophosphate is not reported and sold as a single product in the current market, it is necessary to provide an improved preparation method of lithium pyrophosphate so as to expand the application of lithium pyrophosphate.
Disclosure of Invention
The invention aims to provide a preparation method and application of lithium pyrophosphate, which are characterized in that lithium pyrophosphate is obtained by slowly dripping pyrophosphoric acid into lithium carbonate slurry to react, most of byproducts can be removed by utilizing the fact that lithium carbonate and lithium phosphate are insoluble or slightly soluble in water and filtering, and then the lithium pyrophosphate is separated out by utilizing an alcohol organic solvent to obtain a lithium pyrophosphate product with high purity, small and uniform particles, so that the application of the lithium pyrophosphate product in the field of battery materials is remarkably expanded.
In order to achieve the above object, the present invention provides a method for preparing lithium pyrophosphate, comprising the steps of:
s1, mixing lithium carbonate with water to prepare slurry, then dropwise adding pyrophosphoric acid until the pH reaches 6.5-7.5, and filtering after the reaction is finished;
s2, adding an alcohol organic solvent into the filtrate obtained by filtering in the step S1 until the lithium pyrophosphate is completely separated out, and then filtering;
s3, drying the solid product obtained by filtering in the step S2 to obtain a lithium pyrophosphate product.
The pyrophosphoric acid and lithium carbonate are subjected to acid-base neutralization reaction in an aqueous solution, and the reaction formula is as follows:
2Li 2 CO 3 +H 4 P 2 O 7 ＝Li 4 P 2 O 7 +2H 2 O+2CO 2 ↑
the solubility of lithium carbonate in water is small, and lithium pyrophosphate generated by mixing the lithium carbonate with water to prepare slurry and carrying out liquid phase reaction with pyrophosphoric acid can be dissolved in the water, and the contact efficiency of reaction raw materials can be improved; after the reaction is completed, since the solubility of lithium carbonate and lithium phosphate (which is partially hydrolyzed into phosphoric acid when it is contacted with water and reacts with lithium carbonate to form lithium phosphate) as one of the byproducts in water is small, the lithium phosphate and unreacted lithium carbonate as one of the byproducts can be removed by filtration. And then, by utilizing the characteristic that lithium pyrophosphate is dissolved in water and insoluble in alcohol organic solvents such as methanol or ethanol, the solubility of lithium pyrophosphate in a system is reduced by adding methanol and/or ethanol into the solution, so that a product is precipitated. The whole preparation process is simple and easy to operate, and the product has high purity, small and uniform particle size.
As a further improvement of the present invention, the dropping rate of the pyrophosphate is 4 to 6g/min for each 100g of the reaction scale of the raw material lithium carbonate, and if the reaction scale is enlarged or reduced, the dropping rate is enlarged or reduced in the same proportion as: if 200g of raw material lithium carbonate is taken, the dripping rate is 8-12g/min. By slowly dripping pyrophosphoric acid, lithium carbonate is always in an excessive state, and lithium pyrophosphate can be immediately generated by contact reaction with pyrophosphoric acid, so that the generation of lithium phosphate as a byproduct is reduced as much as possible.
As a further improvement of the invention, the mass ratio of the lithium carbonate to the water is 1:20-25. If the amount of water added is too small, lithium pyrophosphate formed will precipitate when it reaches saturation, resulting in a large amount of loss. According to the invention, the lithium pyrophosphate product can be completely dissolved in water by controlling the liquid-solid ratio, so that the purity of the final purified lithium pyrophosphate product is improved.
As a further development of the invention, step S1 is carried out at 20-30 ℃.
As a further improvement of the present invention, the alcoholic organic solvent includes anhydrous ethanol and/or anhydrous methanol.
As a further improvement of the present invention, step S2 includes: cooling the filtrate in ice bath to 10-15deg.C, adding alcohol organic solvent, stirring for 20-30min, and filtering; the dosage of the alcohol organic solvent is 0.1-1 times of the volume of the filtrate. The cooling is more favorable for precipitation of lithium pyrophosphate, thereby improving the yield.
As a further improvement of the invention, in the step S1, stirring is continued for 10-15min until the reaction is finished after the pyro-acid is added dropwise.
As a further improvement of the present invention, step S3 includes: and (3) adding an alcohol organic solvent into the solid product obtained by filtering in the step (S2) again, stirring and washing for 10-15min, and filtering and drying. The yield can be improved by repeated precipitation of the alcohol organic solvent, the water content in the wet lithium pyrophosphate material before drying can be reduced as much as possible, thus preventing caking during drying and improving the uniformity of the granularity of the lithium pyrophosphate product.
As a further improvement of the present invention, the amount of the alcoholic organic solvent used in step S3 is 0.5 to 1.2 times the mass of the solid product.
As a further improvement of the invention, the drying is carried out for 6-8 hours in a vacuum drying oven with the temperature of 50-60 ℃ and the vacuum degree of-0.08 MPa, thus obtaining the lithium pyrophosphate product.
In some embodiments, a method of preparing lithium pyrophosphate comprises:
1) Pulping by taking a proper amount of high-purity lithium carbonate and pure water according to a solid-to-liquid ratio of 1:20-25, dropwise adding pyrophosphoric acid to adjust the pH of the system to 6.5-7.5, and continuously stirring for 10-15min after the reaction is finished (the excessive lithium carbonate ensures that the pH of the reaction end point is above 6.5);
2) Filtering the reaction solution (filtering to remove unreacted lithium carbonate and a small amount of generated lithium phosphate, wherein the obtained solution is lithium pyrophosphate clean solution), placing the filtrate in a beaker, stirring, adding absolute ethyl alcohol or absolute methyl alcohol with the volume of 0.1-1 times (preferably 0.1-0.2 times) of the filtrate, cooling to 10-15 ℃ in an ice bath after the addition, continuously stirring for 0.5h, and filtering;
3) Stirring the obtained wet material with 0.9-1.1 times of absolute ethyl alcohol or absolute methyl alcohol for 10-15min, and filtering;
4) And drying the stirred wet material in a vacuum drying oven at 50 ℃ and a vacuum degree of-0.08 MPa for 8 hours to obtain a lithium pyrophosphate dry product.
The invention also provides lithium pyrophosphate prepared by any one of the preparation methods. The purity of lithium pyrophosphate is greater than 98%, preferably greater than 99%.
The invention also provides application of the lithium pyrophosphate, which is used for preparing an ionic solid electrolyte, a lithium iron phosphate material coating modifier, a ternary material coating modifier, a positive and negative electrode material conductive agent, a positive electrode material lithium supplementing agent, a negative electrode material pre-lithiation agent, a positive electrode or negative electrode material inorganic conductive adhesive or a solid electrolyte interface agent.
Compared with the prior art, the invention has the following advantages and beneficial effects:
1. short reaction flow, high speed, simple operation, high yield and purity and less byproducts;
2. the invention can react at normal temperature, and has low energy consumption;
3. the methanol or ethanol adopted by the invention is environment-friendly, cheap and easy to obtain;
4. the lithium pyrophosphate precipitated by methanol or ethanol is homogeneously precipitated, and the uniformity of the particle size of the product can be ensured.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the present invention will be clearly and completely described below, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments. 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.
Example 1
Taking 100g of high-purity lithium carbonate (the purity is 99.99%, and the description is omitted), putting the high-purity lithium carbonate into a 3000ml beaker, adding pure water according to the mass ratio of liquid to solid of 22:1, stirring, keeping the temperature at 25+/-2 ℃, then dropwise adding pyrophosphoric acid to adjust the pH of the system to 7.5, keeping stirring for 10min after the dropwise adding is finished, and filtering to obtain about 2200ml of pure lithium pyrophosphate solution (the temperature is 22+/-2 ℃); the clean solution is placed in ice bath for stirring, 200ml of absolute ethyl alcohol is added after the temperature is reduced to 15 ℃, a large amount of white insoluble substances are generated, the stirring is continued for 0.5h, then the filtration is carried out, 186.5g of lithium pyrophosphate wet product is obtained, the stirring and washing with 190g of absolute ethyl alcohol are carried out for 10min, then the filtration is carried out, 125.2g of lithium pyrophosphate wet product is obtained, and then the lithium pyrophosphate wet product is placed in a vacuum drying oven with the vacuum degree of-0.08 MPa for drying at 50 ℃ for 8h, thus obtaining 87.6g of lithium pyrophosphate dry product. The test results are shown in Table 1.
Example 2
Adding 100g of high-purity lithium carbonate into a 3000ml beaker according to a solid-liquid mass ratio of 1:22, stirring, keeping the temperature at 25+/-2 ℃, then dropwise adding pyrophosphoric acid to adjust the pH of the system to 7, keeping stirring for 10min after the dropwise adding is finished, and filtering to obtain 2200ml of pure lithium pyrophosphate solution (the temperature is 22+/-2 ℃); the clean solution is placed in ice bath for stirring, 200ml of absolute ethyl alcohol is added after the temperature is reduced to 15 ℃, a large amount of white insoluble substances are generated, the stirring is continued for 0.5h, then the filtration is carried out, 211.6g of lithium pyrophosphate wet product is obtained, the stirring and washing are carried out for 10min by 200g of absolute ethyl alcohol, 141.5g of lithium pyrophosphate wet product is obtained after the filtration, and the lithium pyrophosphate wet product is placed in a vacuum drying oven with the vacuum degree of-0.08 MPa for drying at 50 ℃ for 8h, thus obtaining 100.5g of lithium pyrophosphate dry product. The test results are shown in Table 1.
Comparative example 1
Adding 100g of high-purity lithium carbonate into a 3000ml beaker according to a solid-liquid mass ratio of 1:22, stirring, keeping the temperature at 25+/-2 ℃, then dropwise adding pyrophosphoric acid to adjust the pH of the system to 5.5, keeping stirring for 10min after the dropwise adding is finished, and filtering to obtain 2200ml of pure lithium pyrophosphate solution (the temperature is 22+/-2 ℃); the clean solution is placed in ice bath for stirring, 200ml of absolute ethyl alcohol is added after the temperature is reduced to 15 ℃, a large amount of white insoluble substances are generated, the stirring is continued for 0.5h, then the filtration is carried out, 224.5g of lithium pyrophosphate wet product is obtained, the stirring and washing are carried out for 10min by 200g of absolute ethyl alcohol, 147.8g of lithium pyrophosphate wet product is obtained after the filtration, and the lithium pyrophosphate wet product is placed in a vacuum drying oven with the vacuum degree of-0.08 MPa for drying at 50 ℃ for 8h, thus obtaining 108.7g of dry product. The test results are shown in Table 1.
Comparative example 2
Taking 100g of high-purity lithium carbonate in a 3000ml beaker, adding pure water according to a solid-liquid mass ratio of 1:22, stirring, keeping the temperature at 25+/-2 ℃, then dropwise adding pyrophosphoric acid to adjust the pH of the system to 7.5, keeping stirring for 10min after the dropwise adding is finished, and filtering to obtain 2000ml of pure lithium pyrophosphate solution (the temperature is 22+/-2 ℃); the clean liquid is placed in ice bath for stirring, and after the temperature is reduced to 15 ℃, the stirring is continued for 0.5h, and no solid is separated out. The process shows that the solubility of lithium pyrophosphate is less affected by temperature at a certain concentration, and the purpose of precipitating lithium pyrophosphate can not be achieved only by cooling.
Comparative example 3
The procedure was as in example 1 except that the addition of lithium pyrophosphate was changed to one-time addition, and the reaction was vigorous at this time, and the solution was likely to boil and overflow the beaker, ending the reaction. The reasons why the operation is not feasible are: the viscosity of the system is high, a large amount of carbon dioxide is generated due to exothermic reaction, the gas cannot be rapidly released after expansion, and meanwhile, the generation of lithium pyrophosphate is affected due to a large amount of byproducts.
Comparative example 4
The procedure was as in example 1, except that 2200ml of purified lithium pyrophosphate was obtained, and after direct evaporation crystallization, 500ml of water was evaporated and filtered, the obtained material was subjected to a solubility test as follows: taking 20g of wet material, adding 100g of pure water, stirring for 10min at normal temperature, and filtering to obtain 18.7g of filter residue. The results show that lithium pyrophosphate deteriorates during the evaporative crystallization into other less soluble phosphates, such as lithium phosphate, lithium metaphosphate. Contrary to the original purpose of the present invention, the evaporative crystallization scheme is not suitable.
The purity of the invention is determined by the content of phosphorus and lithium in the product. The particle size of the product was measured by XRD, the lithium content in the product was measured by ICP, and the results of pyrophosphate, hydrogen pyrophosphate, and dihydrogen pyrophosphate were shown in Table 1, referring to the sodium pyrophosphate anion assay for the food additive (GB 1886.339-2021, titration for pyrophosphate by zinc sulfate heptahydrate, titration for hydrogen pyrophosphate and dihydrogen pyrophosphate by sodium hydroxide). As the pH of the system decreases, a small amount of lithium hydrogen pyrophosphate is produced, resulting in a decrease in the lithium content of the product. Therefore, the lithium pyrophosphate product with higher purity can be obtained by controlling the dropping process and the pH value.
Table 1 results of examples and comparative examples dry basis tests
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limiting; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (10)
1. The preparation method of the lithium pyrophosphate is characterized by comprising the following steps of:
s1, mixing lithium carbonate with water to prepare slurry, then dropwise adding pyrophosphoric acid until the pH reaches 6.5-7.5, and filtering after the reaction is finished;
s2, adding an alcohol organic solvent into the filtrate obtained by filtering until lithium pyrophosphate is completely separated out, and then filtering;
s3, drying the solid product obtained by filtering in the step S2 to obtain a lithium pyrophosphate product.
2. The method for producing lithium pyrophosphate according to claim 1 wherein said dropping rate of said pyrophosphate is 4 to 6g/min.
3. The method for producing lithium pyrophosphate according to claim 1 wherein the mass ratio of said lithium carbonate to water is 1:20 to 25; step S1 is carried out at 20-30 ℃.
4. The method for producing lithium pyrophosphate according to claim 1 wherein said alcoholic organic solvent comprises anhydrous ethanol and/or anhydrous methanol.
5. The method for producing lithium pyrophosphate according to any one of claims 1 to 4 wherein step S2 comprises: cooling the filtrate in ice bath to 10-15deg.C, adding alcohol organic solvent, stirring for 20-30min, and filtering; the dosage of the alcohol organic solvent is 0.1-1 times of the volume of the filtrate.
6. The method for producing lithium pyrophosphate according to claim 1 wherein in step S1, stirring is continued for 10 to 15 minutes until the reaction is completed after the completion of the dropping of said pyrophosphate.
7. The method for producing lithium pyrophosphate according to claim 1 wherein step S3 comprises: and (3) adding an alcohol organic solvent into the solid product obtained by filtering in the step (S2) again, stirring and washing for 10-15min, and filtering and drying.
8. The method for producing lithium pyrophosphate according to claim 7 wherein said alcoholic organic solvent is used in an amount of 0.5 to 1.2 times the mass of said solid product in step S3;
and/or drying in a vacuum drying oven at 50-60 ℃ and a vacuum degree of-0.08 MPa for 6-8 hours to obtain a lithium pyrophosphate product.
9. A lithium pyrophosphate prepared by the preparation method of any one of claims 1 to 8.
10. The use of the lithium pyrophosphate according to claim 9, characterized in that the lithium pyrophosphate is used for the preparation of an ionic solid electrolyte, a lithium iron phosphate material coating modifier, a ternary material coating modifier, a positive and negative electrode material conductive agent, a positive electrode material lithium supplementing agent, a negative electrode material prelithiation agent, a positive or negative electrode material inorganic conductive adhesive or a solid electrolyte interface agent.
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