RU2075435C1 - Method of preparing lithium hexafluorophosphate - Google Patents

Abstract

FIELD: preparation of inorganic compounds. SUBSTANCE: lithium hexafluorophosphate, useful as ionogenic component in electrolytes for chemical power sources with lithium electrode, is prepared by interaction of 1 wt part of lithium fluoride with 2-4 wt parts of phosphorus pentafluoride in hydrogen fluoride followed by filtration of resultant reaction mixture at a temperature from -80 to -50 C and keeping filtered off product at 50-80 and pressure below 10 mm Hg. Purity of final product 99.5-99%, yield in respect to LiF 93-97%. EFFECT: improved procedure. 2 cl, 1 tbl

Description

 The invention relates to a technology for producing lithium hexafluorophosphate, an ionic component of electrolytes for highly efficient rechargeable lithium current sources.

A known method of producing lithium hexafluorophosphate by the interaction of lithium fluoride and phosphorus pentachloride in the environment of liquid hydrogen fluoride [1] in a vessel cooled with nitrogen and a mixture of "dry ice acetone". After the last portion of phosphorus pentachloride was added, the vessel was heated to 0 ^° C and hydrogen fluoride and hydrogen chloride were evaporated from the reaction mixture in a stream of nitrogen. Then the product was separated by filtration and kept at 20 ^o C and a pressure of 20 mm Hg. Purity of the obtained product ≈99% product yield by LiF ≈66% by PCl ₅ ≈ 50%
The disadvantages of the method are the low yield of the product, its insufficient purity for use as an ionic component in lithium chemical current sources (CHIT) and extremely corrosive environment (a mixture of HF and HCl). In addition, when using very hygroscopic phosphorus pentachloride, the possibility of water entering the system is not ruled out, while a low moisture content is one of the most important requirements for lithium ChIT components.

 Closest to the claimed method according to the technical essence is a method for producing lithium hexafluorophosphate by the interaction of lithium fluoride and phosphorus pentafluoride in a solution of hydrogen fluoride [2] (prototype).

In a reactor containing a solution of lithium fluoride in hydrogen fluoride with a mass ratio of LiF: HF equal to 1:12, at a temperature of about 25 ^o C serves phosphorus pentafluoride to a predetermined pressure and maintain the reaction mixture for 24 hours. The excess phosphorus pentafluoride and the hydrogen fluoride solvent are distilled off from the reaction mixture, the resulting lithium hexafluorophosphate having a purity of 92.1% LiF yield is approximately 73%. Next, lithium hexafluorophosphate is purified using acetonitrile as follows: the complex compound Li (CH ₃ CN) _{4 is} synthesized PF ₆ , impurities are separated from it (they do not bind to the complex compound), then LiPF _{6 with a} purity of more than 99% is obtained by decomposition of Li (CH ₃ CN) ₄ PF ₆
The method has the following disadvantages: low purity of the product isolated directly from the reaction mixture and, as a consequence, the need for additional labor-intensive cleaning operations using acetonitrile, as well as a low yield of the product.

 The objective of the invention is to obtain high purity lithium hexafluorophosphate (> 99%) in high yield by isolation directly from the reaction mixture, i.e. no additional cleaning operation.

The problem is solved in that in the method for producing lithium hexafluorophosphate, comprising the interaction of lithium fluoride and phosphorus pentafluoride in hydrogen fluoride and the isolation of the target product from the reaction mixture, lithium fluoride and hydrogen fluoride are taken in a mass ratio of 1: (2 ^° C4), and the obtained as a result of interaction, the reaction mixture is filtered at a temperature of from -80 to -50 ^o C.

The filtered product is maintained at a pressure of less than 10 mm Hg. and temperature +50 ^o C + 80 ^o C.

The method is as follows. The reactor is placed lithium fluoride and hydrogen fluoride in a predetermined amount (ratio from 1: 2 to 1: 4), the reactor is cooled to -50 ^o C and fed into it phosphorus pentafluoride. At the indicated ratio, the yield of the product and its quality, as shown by experimental studies, are the best. After the reaction, the reaction mixture (suspension) is cooled to a temperature of -80 ^o C-50 ^o C and filtered at this temperature through a Nickel mesh. When the temperature drops below -80 ^o C, the mixture begins to freeze, and an increase in temperature above -50 ^o C reduces the yield and reduces the quality of the product. The filtered precipitate is kept in vacuum (less than 10 mm Hg) at a temperature of +50 ^o C + 80 ^o C. This temperature range is due to the desire to most completely remove the remaining hydrogen fluoride and minimize thermal decomposition of lithium hexafluorophosphate. The experimental data are given in the table.

 As can be seen from the table, as a result of the implementation of the proposed method receive lithium hexafluorophosphate with a basic substance content of 99.5 to 99.7% with a yield on LiF from 93 to 97% (experiments 1-4). The method provides the target product with a high degree of purification and with a high yield without additional purification.

Claims (2)

1. A method of producing lithium hexafluorophosphate, comprising reacting lithium fluoride and phosphorus pentafluoride in hydrogen fluoride and isolating the target product from the reaction mixture, characterized in that lithium fluoride and hydrogen fluoride are taken in a mass ratio of 1 (2 4), and the resulting the reaction mixture is filtered at a temperature of from -80 to -50 ^o C. 2. The method according to p. 1, characterized in that the filtered product is maintained at a pressure of less than 10 mm Hg and a temperature of 50 to 80 ^o C.

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