CN115159494B - Preparation method of lithium difluorophosphate - Google Patents
Preparation method of lithium difluorophosphate Download PDFInfo
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- CN115159494B CN115159494B CN202211062678.3A CN202211062678A CN115159494B CN 115159494 B CN115159494 B CN 115159494B CN 202211062678 A CN202211062678 A CN 202211062678A CN 115159494 B CN115159494 B CN 115159494B
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- C01B25/00—Phosphorus; Compounds thereof
- C01B25/16—Oxyacids of phosphorus; Salts thereof
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- C01B25/455—Phosphates containing halogen
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Abstract
The invention discloses a preparation method of lithium difluorophosphate, which comprises the following steps: 4Li 2 O+2P+5F 2 =2LiPO 2 F 2 +6LiF 1) under inert atmosphere, adding lithium oxide and yellow phosphorus into a non-aqueous solventDispersing to obtain a dispersion liquid; 2) Introducing mixed gas of fluorine and nitrogen into the dispersion liquid for reaction, and filtering after the reaction to obtain a mixture of lithium difluorophosphate and lithium fluoride; returning the filtrate to the step 1) for recycling; the molar ratio of lithium oxide, fluorine gas and yellow phosphorus is (2-8): 2.5-10): 1; 3) Adding a solvent into the mixture of lithium difluorophosphate and lithium fluoride obtained in the step 2) for dissolving, and filtering to obtain lithium fluoride; concentrating and filtering the filtrate, and drying a filter cake to obtain a lithium difluorophosphate finished product; the whole process system does not need to remove water and introduce other metal cations, and the obtained lithium difluorophosphate has high purity and high yield.
Description
Technical Field
The invention belongs to the field of nonaqueous electrolyte batteries, and particularly relates to a preparation method of lithium difluorophosphate.
Background
The lithium battery is a clean energy, the most applied field at present is electric vehicles, the lithium battery has no memory, high safety and no pollution, and is an important clean energy for realizing and implementing a sustainable development concept. In recent years, domestic lithium batteries are widely applied in various fields, and particularly, large-scale application of power batteries and energy storage batteries makes lithium batteries become a global industry which is continuously expanded.
Lithium difluorophosphate of formula LiPO 2 F 2 White powdery solid, melting point 340 ℃, is exposed to air, is easy to absorb moisture in air and shows acidity. Lithium difluorophosphate is mainly used as an additive of lithium battery electrolyte. Research shows that a small amount of lithium difluorophosphate is added into a lithium hexafluorophosphate electrolyte system, so that the high-low temperature cycle performance of the battery can be obviously improved.
Currently, the mainstream method for preparing lithium difluorophosphate is to react lithium hexafluorophosphate with lithium carbonate to generate lithium difluorophosphate, lithium fluoride and carbon dioxide. The process mainly has the defects of high raw material price, complex process, high energy consumption, difficult product separation and purification, low yield and the like, and is not beneficial to industrialized implementation.
Therefore, the development of a method for preparing lithium difluorophosphate with simple process, high reaction efficiency and good product performance is urgently needed.
Disclosure of Invention
The invention provides a novel process for preparing lithium difluorophosphate. According to the invention, lithium oxide, phosphorus and fluorine gas which are cheaper and easily available are used for reaction, lithium difluorophosphate is directly synthesized by a one-pot method, the process is simpler, the cost is lower, and the resource value is maximized.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of lithium difluorophosphate comprises the following steps:
4Li 2 O + 2P + 5F 2 = 2LiPO 2 F 2 + 6LiF
1) Under inert atmosphere, adding lithium oxide and yellow phosphorus into a non-aqueous solvent for dispersion to obtain a dispersion liquid;
2) Introducing mixed gas of fluorine and nitrogen into the dispersion liquid for reaction, and filtering after the reaction to obtain a mixture of lithium difluorophosphate and lithium fluoride; returning the filtrate to the step 1) for recycling; the molar ratio of lithium oxide, fluorine gas and yellow phosphorus is (2-8): 2.5-10): 1;
3) Adding a solvent into the mixture of lithium difluorophosphate and lithium fluoride obtained in the step 2) for dissolving, and filtering to obtain lithium fluoride; concentrating and filtering the filtrate, and drying the filter cake to obtain the finished lithium difluorophosphate.
Further, the yellow phosphorus in the step 1) needs to be dehydrated, the yellow phosphorus is washed by ethanol, the amount of the ethanol is 5-10 times of the mass of the yellow phosphorus, and then the yellow phosphorus is dried by nitrogen.
Further, the non-aqueous solvent in step 1) refers to a solvent which does not react with fluorine gas, including but not limited to perfluoropolyether, and 100g of perfluoropolyether is added per 0.09mol of yellow phosphorus. The mass ratio of the solvent to the (lithium oxide + yellow phosphorus) in the step 1) is (5-20) to 1.
Further, the reaction temperature in the step 2) is 10-80 ℃; the reaction time is 30-400min.
Further, the volume ratio of the fluorine gas in the fluorine-nitrogen mixed gas is 10 to 20%, and the flow rate of the fluorine-nitrogen mixed gas is 200 to 500 mL/min.
Further, in the step 3), one or more of tetrahydrofuran, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, acetone and acetonitrile are used for dissolving. The mass ratio of the solvent to the lithium difluorophosphate + the lithium fluoride is (3-10): 1.
By adopting the technical scheme, the process is simple to operate, the whole process system does not need to remove water and introduce other metal cations without by-producing water, the obtained lithium difluorophosphate has high purity and high yield, the by-product is easy to treat, the solvent can be recycled, and the production cost is greatly reduced.
Drawings
FIG. 1 is an XRD pattern of lithium difluorophosphate obtained in example 1; wherein, 21.42 degrees, 23.94 degrees and 36.34 degrees are the peaks of the valve bag.
Detailed Description
The following examples are provided to further illustrate the practice of the invention.
The yellow phosphorus in the following examples requires dehydration treatment, which comprises the following specific steps: washing twice with anhydrous alcohol, each time using 5 times of the weight of yellow phosphorus, and blowing with nitrogen.
Example 1
A preparation method of lithium difluorophosphate comprises the following steps:
1) The PFA bottle was replaced with nitrogen, primed with 100g of perfluoropolyether, and charged with 2.87g (0.09 mol) of yellow phosphorus and 5.6g (0.18 mol) of lithium oxide. Heating the oil bath to 50 ℃, starting stirring, introducing a fluorine-nitrogen mixed gas when the yellow phosphorus is molten, controlling the flow rate to be 450mL/min and the introduction time of the fluorine-nitrogen mixed gas to be 130min (the dosage of the fluorine gas is 0.26 mol), and cooling to room temperature after the reaction is finished, wherein the volume ratio of the fluorine gas in the fluorine-nitrogen mixed gas is 10%.
2) The mixture was filtered to obtain 16.74g of a mixture of lithium difluorophosphate and lithium fluoride, and the mixture was dissolved in 100g of ethyl acetate and filtered again to obtain a filter cake of lithium fluoride. Concentrating the filtrate at 50 ℃ and-0.095 MPa, wherein the concentrated solution weighs 20.3g (the concentrated crystal is lithium difluorophosphate), filtering (the filtrate can be recycled and used for dissolving a mixture of lithium difluorophosphate and lithium fluoride), and drying the solid for 4h at 100 ℃ under the protection of nitrogen to obtain 9.52g of a lithium difluorophosphate finished product with the purity of 99.98% and the yield of 95.2%.
Fig. 1 is an XRD pattern of the obtained lithium difluorophosphate (in order that the sample does not contact moisture in the air, the whole sample needs to be wrapped with a polyethylene valve bag for testing), which proves the successful synthesis and high purity of lithium difluorophosphate.
Example 2
A preparation method of lithium difluorophosphate comprises the following steps:
1) The PFA bottle was replaced with nitrogen, primed with 100g of perfluoropolyether, and charged with 2.87g (0.09 mol) of yellow phosphorus and 5.6g (0.18 mol) of lithium oxide. Heating the oil bath to 70 ℃, starting stirring, introducing a fluorine-nitrogen mixed gas when the yellow phosphorus is molten, controlling the flow rate to be 250ml/min and the introduction time of the fluorine-nitrogen mixed gas to be 100min (the dosage of the fluorine gas is 0.225 mol), and cooling to room temperature after the reaction is finished.
2) The mixture of lithium difluorophosphate and lithium fluoride (16.83 g) was obtained by filtration, and the mixture was dissolved in 100g of ethyl acetate and filtered again to obtain a filter cake of lithium fluoride. Concentrating the filtrate at 45 ℃ and-0.095 MPa, filtering the concentrated solution to obtain 19.7g (the concentrated crystal is lithium difluorophosphate), drying the solution for 4h at 100 ℃ under the protection of nitrogen to obtain 9.68g of lithium difluorophosphate finished product with the purity of 99.98% and the yield of 96.8%. The lithium difluorophosphate obtained in example 2 was examined by X-ray diffraction and the XRD results were obtained similarly to example 1, indicating that the objective compound was obtained.
Example 3
A preparation method of lithium difluorophosphate comprises the following steps:
1) The PFA bottle was replaced with nitrogen, primed with 100g of perfluoropolyether, and charged with 2.87g (0.09 mol) of yellow phosphorus and 6.16g (0.198 mol) of lithium oxide. Heating the oil bath to 70 ℃, starting stirring, introducing a fluorine-nitrogen mixed gas when the yellow phosphorus is molten, controlling the flow rate to be 250ml/min and the introduction time of the fluorine-nitrogen mixed gas to be 110min (the dosage of the fluorine gas is 0.24 mol), and cooling to room temperature after the reaction is finished, wherein the volume ratio of the fluorine gas in the fluorine-nitrogen mixed gas is 20%.
2) The mixture was filtered to obtain 17.77g of a mixture of lithium difluorophosphate and lithium fluoride, and the mixture was dissolved in 100g of ethyl acetate and filtered again to obtain a filter cake of lithium fluoride. Concentrating the filtrate at 45 ℃ and-0.095 MPa, filtering the concentrated solution to obtain 20.5g of solution (the concentrated crystal is lithium difluorophosphate), drying the solution for 4h at 100 ℃ under the protection of nitrogen to obtain 9.72g of lithium difluorophosphate finished product with the purity of 99.98% and the yield of 97.2%. When the lithium difluorophosphate obtained in example 3 was examined by X-ray diffraction, the XRD results thereof were similar to those of example 1, indicating that the objective compound was obtained.
The lithium difluorophosphate-containing products obtained in example 1, example 2 and example 3 were examined, and the results are shown in Table 1, respectively.
Table 1 test results of lithium difluorophosphate products obtained in examples
As can be seen from the data in the table, the lithium difluorophosphate product prepared by the method has high purity and low impurity content, and meets the use requirement of the lithium battery electrolyte.
Finally, it should be noted that: the present invention is illustrated in detail by the examples described above, but the present invention is not limited to the details described above, i.e., it is not intended that the present invention be implemented by relying on the details described above. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.
Claims (8)
1. A preparation method of lithium difluorophosphate is characterized by comprising the following steps:
4Li 2 O + 2P + 5F 2 = 2LiPO 2 F 2 + 6LiF
1) Under inert atmosphere, adding lithium oxide and yellow phosphorus into a non-aqueous solvent for dispersion to obtain a dispersion liquid;
2) Introducing mixed gas of fluorine and nitrogen into the dispersion liquid for reaction, and filtering after the reaction to obtain a mixture of lithium difluorophosphate and lithium fluoride; returning the filtrate to the step 1) for recycling; the molar ratio of lithium oxide, fluorine gas and yellow phosphorus is (2-8): 2.5-10): 1;
3) Adding a solvent into the mixture of lithium difluorophosphate and lithium fluoride obtained in the step 2) for dissolving, and filtering to obtain lithium fluoride; concentrating and filtering the filtrate, and drying the filter cake to obtain a lithium difluorophosphate finished product.
2. The method for preparing lithium difluorophosphate as claimed in claim 1, wherein the yellow phosphorus in step 1) is dehydrated by washing with absolute ethanol and blowing with nitrogen.
3. The method for preparing lithium difluorophosphate according to claim 1, wherein the non-aqueous solvent used in step 1) is a solvent which does not react with fluorine gas, and includes, but is not limited to perfluoropolyether.
4. The method for producing lithium difluorophosphate according to claim 1, wherein the amount of the solvent used in the step 1) is 5 to 20 times the sum of the amounts by mass of lithium oxide and yellow phosphorus.
5. The method for producing lithium difluorophosphate according to claim 1, wherein the reaction temperature in the step 2) is 10 to 80 ℃; the reaction time is 30 min-400 min.
6. The method for preparing lithium difluorophosphate according to claim 1, wherein the volume ratio of the fluorine gas in the mixed fluorine-nitrogen gas is 10 to 20%, and the flow rate of the mixed fluorine-nitrogen gas is 200 to 500 mL/min.
7. The method for preparing lithium difluorophosphate as claimed in claim 1, wherein the solvent used in step 3) is one or more selected from tetrahydrofuran, methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol, ethylene glycol dimethyl ether, ethylene glycol diethyl ether, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, dimethyl carbonate, diethyl carbonate, acetone and acetonitrile.
8. The method for preparing lithium difluorophosphate according to claim 1, wherein in the step 3), the amount of the solvent is 3 to 10 times the amount of the mixture of lithium difluorophosphate and lithium fluoride.
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