CN115535995A - Purification method of lithium difluorophosphate - Google Patents
Purification method of lithium difluorophosphate Download PDFInfo
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- CN115535995A CN115535995A CN202211368146.2A CN202211368146A CN115535995A CN 115535995 A CN115535995 A CN 115535995A CN 202211368146 A CN202211368146 A CN 202211368146A CN 115535995 A CN115535995 A CN 115535995A
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- C01B25/00—Phosphorus; Compounds thereof
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Abstract
The invention discloses a purification method of lithium difluorophosphate, which comprises the following steps: (1) Under nitrogen atmosphere, dissolving the lithium difluorophosphate crude product in an aprotic polar organic solvent to obtain a lithium difluorophosphate crude product solution; (2) Adding an organic alkaline compound into the lithium difluorophosphate crude product solution, and stirring for reaction at a certain temperature; (3) And filtering the reaction solution after reaction, concentrating the filtrate, adding a non-polar organic solvent, washing and drying to obtain a purified lithium difluorophosphate product. The purification method has the advantages of simple process, simple and convenient operation, difficult generation of impurities, and higher purity of the lithium difluorophosphate product obtained after purification.
Description
Technical Field
The invention belongs to the technical field of lithium ion batteries, and particularly relates to a purification method of lithium difluorophosphate.
Background
Lithium difluorophosphate can be used as an additive of lithium ion battery electrolyte. Research shows that a certain amount of lithium difluorophosphate is added into an electrolyte system with lithium hexafluorophosphate as an electrolyte, so that the high-temperature cycle performance and the high-temperature storage performance of the lithium ion battery can be obviously improved. Lithium difluorophosphate is added into the electrolyte, and a stable solid electrolyte interface film can be formed on the surface of the positive electrode, so that the safety performance, the cycle performance and the service life of the battery are improved.
At present, the main preparation method of lithium difluorophosphate is to react lithium hexafluorophosphate with oxygen atom providing compounds such as water and siloxane raw materials. The method can generally obtain a lithium difluorophosphate product with higher purity, but because the lithium hexafluorophosphate serving as a reaction raw material has poor heat sensitivity and stability, a small amount of decomposition or other side reactions inevitably occur in the chemical reaction process to form acidic impurities such as hydrofluoric acid, monofluorophosphoric acid and the like. The acidic impurities are high in fluoride ion concentration in the detection of purity by ion chromatography, and high in acid value (calculated by hydrofluoric acid) in the detection of acidity, and are usually over 100 ppm.
Aiming at the purification method of lithium difluorophosphate, the technical means reported in the prior publication adopts carbonate, hydroxide, halide or alkaline lithium salt of alkali metal to react under heating, and then the alkali metal is removed by filtration. And reacting alkali metal carbonate and hydroxide used as impurity removal reaction with acidic impurities in lithium difluorophosphate to generate water, and continuously performing side reaction on the water and the lithium difluorophosphate to generate impurities. Meanwhile, the method has longer impurity removal reaction time, for example, the reaction time is 1-48 hours as disclosed in the patent No. CN201911177879.6, and after the impurity removal reaction is finished, the post-treatment is carried out by adopting a recrystallization method, the recrystallization temperature is-50 to-10 ℃, and the energy consumption is higher.
Disclosure of Invention
In order to solve the technical problems, the invention aims to provide a method for purifying lithium difluorophosphate; the purification method has the advantages of simple process, simple and convenient operation, difficult generation of impurities, and higher purity of the lithium difluorophosphate product obtained after purification.
In order to achieve the technical purpose and achieve the technical effect, the invention is realized by the following technical scheme:
a purification method of lithium difluorophosphate comprises the following steps:
(1) Under nitrogen atmosphere, dissolving the lithium difluorophosphate crude product in an aprotic polar organic solvent to obtain a lithium difluorophosphate crude product solution;
(2) Adding an organic alkaline compound into the lithium difluorophosphate crude product solution, and stirring for reaction at a certain temperature;
(3) And filtering the reaction solution after reaction, concentrating the filtrate, adding a non-polar organic solvent, washing and drying to obtain a purified lithium difluorophosphate product.
Preferably, the aprotic polar organic solvent is one or a mixture of two or more selected from methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetone and acetonitrile.
Further, the water content of the aprotic polar organic solvent is controlled to be within 500ppm, preferably within 300ppm, and more preferably within 100 ppm; the addition amount of the aprotic polar organic solvent is 3 to 8 times of the mass of the lithium difluorophosphate.
Preferably, the organic basic compound is a nitrogen-containing weak organic base selected from one or a mixture of two or more of triethylamine, n-propylamine, isopropylamine, dipropylamine, tripropylamine, butylamine, isobutylamine, tert-butylamine, hexylamine, octylamine, aniline, cyclohexylamine, pyridine and piperidine.
Further, the adding amount of the organic alkaline compound is 1-3 times of the molar amount of acid (calculated by hydrofluoric acid) in the lithium difluorophosphate product.
Further, the temperature of the stirring reaction in the step (2) is 0-60 ℃, and the reaction time is 0.5-5 hours.
Preferably, the non-polar organic solvent is one or a mixture of two or more selected from dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, benzene, toluene, xylene, chlorobenzene, hexane, cyclohexane, heptane, octane, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, and petroleum ether.
The invention has the beneficial effects that:
the organic alkaline compound can be subjected to chelation reaction with acidic impurities in the lithium difluorophosphate crude product, and ammonium salt substances formed by chelation are precipitated in the aprotic polar organic solvent in a solid form and can be removed by simple filtration.
Compared with the prior purification technology adopting solid alkaline salt, the method adopts the organic alkaline compound (organic amine weak base) as liquid, and the organic alkaline compound reacts with the dissolved lithium difluorophosphate solution in a homogeneous phase manner, so that the reaction is quicker and more thorough, and the quantitative reaction can be almost realized. The excessive or unreacted trace organic alkaline compound is liquid, and can be fully taken out of the system through concentration and washing by a non-polar solvent.
The purification method has simple process, easy operation and difficult generation of impurities, the purity of the obtained lithium difluorophosphate product can reach more than 99.9 percent, the acidity (calculated by HF) is remained within 50ppm, and the high-standard requirements of the lithium battery industry can be fully met.
Detailed Description
The technical solutions in the present invention will be described clearly and completely with reference to specific embodiments, and it should be understood that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The invention provides a purification method of lithium difluorophosphate, which comprises the following steps:
(1) Under nitrogen atmosphere, dissolving the lithium difluorophosphate crude product in an aprotic polar organic solvent to obtain a lithium difluorophosphate crude product solution;
(2) Adding an organic alkaline compound into the lithium difluorophosphate crude product solution, and stirring and reacting for 0.5-5 hours at the temperature of 0-60 ℃;
(3) And filtering the reaction solution after the reaction, concentrating the filtrate until solid is separated out, adding a non-polar organic solvent, washing and drying to obtain a purified lithium difluorophosphate product.
Wherein the aprotic polar organic solvent is selected from one or a mixture of more than two of methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetone and acetonitrile.
Wherein the water content of the aprotic polar organic solvent is controlled to be within 500ppm, preferably within 300ppm, more preferably within 100 ppm; the addition amount of the aprotic polar organic solvent is 3-8 times of the mass of the lithium difluorophosphate.
Wherein the organic alkaline compound is a nitrogen-containing organic weak base which is selected from one or a mixture of more than two of triethylamine, n-propylamine, isopropylamine, dipropylamine, tripropylamine, butylamine, isobutylamine, tert-butylamine, hexylamine, octylamine, aniline, cyclohexylamine, pyridine and piperidine. The addition amount of the organic alkaline compound is 1-3 times of the molar amount of the acid content in the lithium difluorophosphate product.
Wherein the nonpolar organic solvent is selected from one or more of dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, benzene, toluene, xylene, chlorobenzene, hexane, cyclohexane, heptane, octane, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane and petroleum ether.
The present invention will be further described with reference to specific examples.
Example 1
200g of crude lithium difluorophosphate (ion chromatography purity 99.25%, acidity 132 ppm) was charged into a three-necked flask with stirring under nitrogen atmosphere, and 1200g of ethyl acetate with a water content of 65ppm was added and stirred until completely dissolved to obtain a crude lithium difluorophosphate solution.
Calculating acidity by using HF, adding 0.4g of triethylamine with 3 times of molar weight into the lithium difluorophosphate crude product solution under stirring, and reacting for 5 hours under stirring at 0-10 ℃; filtering with 0.45 μm PTFE filter membrane under nitrogen protection, concentrating the filtrate under reduced pressure until solid is separated out, adding 200g dimethyl carbonate, stirring, washing, filtering under reduced pressure, vacuum drying the solid, weighing 183g, and detecting IC to obtain purity of 99.93%; the acid value is 25ppm by titration detection; the purification yield was 91.5%.
Example 2
300g of crude lithium difluorophosphate (ion chromatography purity 99.18%, acidity 285 ppm) was charged into a three-necked flask with stirring under a nitrogen atmosphere, and 2400g of acetonitrile with a water content controlled to 120ppm was added thereto and stirred until completely dissolved to obtain a crude lithium difluorophosphate solution.
Calculating acidity by using HF, adding 0.68g of pyridine with the molar weight of 2 times into the lithium difluorophosphate crude product solution under stirring, heating to 50-60 ℃, stirring for reaction, and cooling to room temperature after 0.5 hour; filtering with 0.1 μm PTFE filter membrane under nitrogen protection, concentrating the filtrate under reduced pressure, adding 300g dichloromethane, stirring, washing, filtering under reduced pressure, vacuum drying the solid, weighing 266g, and detecting IC with purity of 99.91%; the acid value is 8ppm by titration detection; the purification yield was 88.7%.
Example 3
150g of lithium difluorophosphate crude product (ion chromatography purity 99.35%, acidity 158 ppm) was charged into a three-necked flask with stirring under nitrogen atmosphere, and 450g of ethylene glycol dimethyl ether with a water content of 86ppm was added thereto and stirred until completely dissolved, thereby obtaining a lithium difluorophosphate crude product solution.
Calculating acidity by using HF, adding 0.18g of cyclohexylamine with 1.5 times of molar weight into the lithium difluorophosphate crude product solution under stirring, and reacting for 2 hours under stirring at room temperature; filtering with 0.45 μm PTFE filter membrane under nitrogen protection, concentrating the filtrate under reduced pressure, adding 150g toluene, stirring, washing, filtering under reduced pressure, vacuum drying the solid, weighing 129g, and detecting IC to obtain 99.92% purity; the acid value is 18ppm by titration detection; the purification yield was 86%.
Example 4
200g of lithium difluorophosphate product (with the ion chromatographic purity of 98.6 percent and the acidity of 180 ppm) is added into a three-neck flask with a stirrer under nitrogen atmosphere, then 1000g of acetone with the water content controlled at 150ppm is added and stirred until the acetone is completely dissolved, and a crude lithium difluorophosphate solution is prepared.
Calculating acidity by using HF, adding 0.33g of triethylamine with the molar weight being 1.8 times that of the lithium difluorophosphate crude product solution into the solution under stirring, and reacting the solution for 1 hour under stirring at the temperature of between 35 and 45 ℃; filtering with 0.1 μm PTFE filter membrane under nitrogen protection, concentrating the filtrate under reduced pressure, adding 200g petroleum ether, stirring, washing, filtering under reduced pressure, vacuum drying the solid, weighing 186g, and detecting IC to obtain a product with purity of 99.92%; the acid value is 13ppm by titration detection; the purification yield was 93%.
From the above examples, it can be seen that the lithium difluorophosphate product obtained by the purification method of the present invention has high yield and high purity, and the acidity (calculated as HF) remains within 50ppm, which can sufficiently meet the high standard requirements of the lithium battery industry.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications and equivalents made by the contents of the present invention or directly or indirectly applied to other related technical fields are included in the scope of the present invention.
Claims (7)
1. A method for purifying lithium difluorophosphate is characterized by comprising the following steps:
(1) Under nitrogen atmosphere, dissolving a lithium difluorophosphate crude product into an aprotic polar organic solvent to obtain a lithium difluorophosphate crude product solution;
(2) Adding an organic alkaline compound into the lithium difluorophosphate crude product solution, and stirring for reaction at a certain temperature;
(3) And filtering the reaction solution after the reaction, concentrating the filtrate, adding a non-polar organic solvent, washing, and drying to obtain a purified lithium difluorophosphate product.
2. The method for purifying lithium difluorophosphate as claimed in claim 1, wherein the aprotic polar organic solvent is one or a mixture of two or more selected from methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, acetone and acetonitrile.
3. The method for purifying lithium difluorophosphate according to claim 1, wherein the water content of the aprotic polar organic solvent is controlled to be within 500ppm, and the addition amount of the aprotic polar organic solvent is 3 to 8 times of the mass of the lithium difluorophosphate.
4. The method of claim 1, wherein the organic basic compound is a nitrogen-containing weak organic base selected from one or a mixture of two or more of triethylamine, n-propylamine, isopropylamine, dipropylamine, tripropylamine, butylamine, isobutylamine, tert-butylamine, hexylamine, octylamine, aniline, cyclohexylamine, pyridine, and piperidine.
5. The method for purifying lithium difluorophosphate as claimed in claim 1, wherein the organic basic compound is added in an amount of 1 to 3 times by mol as much as the acid content in the lithium difluorophosphate product.
6. The method for purifying lithium difluorophosphate according to claim 1, wherein the stirring reaction in the step (2) is carried out at a temperature of 0 to 60 ℃ for a reaction time of 0.5 to 5 hours.
7. The method of claim 1, wherein the non-polar organic solvent is one or a mixture of two or more selected from the group consisting of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, benzene, toluene, xylene, chlorobenzene, hexane, cyclohexane, heptane, octane, dichloromethane, dichloroethane, trichloroethane, tetrachloroethane, and petroleum ether.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN106882782A (en) * | 2017-03-25 | 2017-06-23 | 山东永浩新材料科技有限公司 | A kind of synthetic method of difluorophosphate |
| CN107381530A (en) * | 2017-08-23 | 2017-11-24 | 中山大学 | A kind of method of purification of difluorophosphate |
| CN109941982A (en) * | 2017-12-21 | 2019-06-28 | 江苏国泰超威新材料有限公司 | A kind of method of purification of difluorophosphate |
| CN113247871A (en) * | 2021-06-04 | 2021-08-13 | 江苏华盛锂电材料股份有限公司 | Preparation method of lithium bis (fluorosulfonyl) imide |
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- 2022-11-03 CN CN202211368146.2A patent/CN115535995A/en active Pending
Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN106882782A (en) * | 2017-03-25 | 2017-06-23 | 山东永浩新材料科技有限公司 | A kind of synthetic method of difluorophosphate |
| CN107381530A (en) * | 2017-08-23 | 2017-11-24 | 中山大学 | A kind of method of purification of difluorophosphate |
| CN109941982A (en) * | 2017-12-21 | 2019-06-28 | 江苏国泰超威新材料有限公司 | A kind of method of purification of difluorophosphate |
| CN113247871A (en) * | 2021-06-04 | 2021-08-13 | 江苏华盛锂电材料股份有限公司 | Preparation method of lithium bis (fluorosulfonyl) imide |
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