PRODUCTION OF LITHIUM HEXAFLUOROPHOSPHATE

Abstract

A method of producing solid lithium hexafluorophosphate (LiPF.sub.6) includes reacting lithium fluoride (LiF) in solid form with gaseous phosphorous pentafluoride (PF.sub.5) in a liquid perhalogenated organic compound that is non-reactive with, i.e. is inert to, the PF.sub.5, thereby producing LiPF.sub.6 in solid form.

Claims

1. A method of producing lithium hexafluorophosphate (LiPF.sub.6) in solid form, the method including reacting lithium fluoride (LiF) in solid form with gaseous phosphorous pentafluoride (PF.sub.5), wherein the reaction is performed in a liquid perhalogenated organic compound that is inert to the PF.sub.5 and is a solvent for the PF.sub.5, thereby producing LiPF.sub.6 in solid form.

2. The method according to claim 1, wherein reacting the LiF with gaseous PF.sub.5 includes dispersing the LiF in solid form in the liquid medium; and dissolving gaseous PF.sub.5 in the liquid medium containing the LiF in solid form.

3. The method according to claim 1, wherein the perhalogenated organic compound is a perfluorocarbon.

4. The method according to claim 3, wherein the perfluorocarbon is selected from cyclic and non-cyclic perfluoroalkanes, and cyclic and non-cyclic perfluoroalkenes, and mixtures of any two or more thereof, severally or jointly.

5. The method according to claim 1, wherein the perfluorocarbon is selected from perfluorodecalin, perfluoroheptane, hexafluorobenzene, tetrafluoroethylene, and mixtures of any two or more thereof.

6. (canceled)

7. A method of producing an electrolyte, the method including producing LiPF.sub.6 in solid form according to the method of claim 1; and dissolving the LiPF.sub.6 in solid form in a solvent for LiPF.sub.6.

8. The method according to claim 7, wherein the solvent for LiPF.sub.6 is selected from ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, and mixtures thereof.

9. (canceled)

10. A method of manufacturing an electric battery, the method including producing an electrolyte according to the method of claim 7; and including the electrolyte in an electric battery.

Description

EXAMPLES

[0072] EMBODIMENTS OF THE INVENTION will now be described by way of example only, with reference to the following examples.

Example 1: Reaction between LiF and PF.SUB.5 .Gas in the Presence of a Cyclic or Polycyclic Perfluorocarbon Solvent

[0073] A clean, thick-walled stainless-steel reactor capable of handling more than 10 bar of gas pressure was loaded with 2 g of LiF solid powder purchased from Sigma-Aldrich or Alpha-Aesar.

[0074] 60 ml liquid perfluorodecalin was added into the reactor, with the LiF thus becoming suspended in the perfluorodecalin.

[0075] The reactor was then sealed in a glovebox and connected to a system consisting of a vacuum line, a high-pressure indicator and a high-pressure PF.sub.5 gas cylinder.

[0076] PF.sub.5 gas was introduced from its feed cylinder into the reactor, thus contacting the suspension of LiF in perfluorodecalin.

[0077] PF.sub.5 feeding into the reactor continued until the equilibrium was achieved, which was maintained (increase in PF.sub.5 gas pressure maintained at 7 bar).

[0078] The reaction was allowed to digest for at least 1 day.

[0079] Excess PF.sub.5 gas was removed from the reactor by cycle purging and then applying vacuum.

[0080] The reactor was then transferred to a nitrogen glove box for opening in a dry, inert environment.

[0081] An off-white dense liquid with gel on the reactor sides was recovered and filtered.

[0082] The retentate was dried using nitrogen in a glovebox and a mixture of unreacted LiF and formed LiPF.sub.6, which was previously in suspension in the liquid medium, was recovered in solid form.

[0083] The reaction that took place is in accordance with reaction equation 1:

LiF(s)+PF.sub.5(g).fwdarw.LiPF.sub.6(s) (Eq. 1)

[0084] LiPF.sub.6 was recovered from the mixture of LiPF.sub.6 and unreacted LiF using a solvent for LiPF.sub.6. Conversion of LiF in excess of 90% have been observed, with LiPF.sub.6 recovery of up to 99%.

[0085] Suitable solvents include ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, or combinations thereof.

Example 2: A Reaction between LiF and PF.SUB.5 .Gas in the Presence of Non-Cyclic or Branched Perfluorocarbon Solvent

[0086] LiF in solid form is dispersed in liquid perfluoroheptane or any non-cyclic perfluorocarbons of range C.sub.1F.sub.4, and C.sub.6F.sub.14 to C.sub.9F.sub.20 liquid.

[0087] The reaction that takes place is in accordance with reaction equation 1.

[0088] The reaction temperature range is 94 C. to 127 C.

[0089] The reaction pressure range is 0 kPa to 3 000 kPa, more preferably up to 1000 kPa.

[0090] Up to 99% recovery of LiPF.sub.6 may be achieved when produced LiPF.sub.6 is dissolved in a solvent for LiPF.sub.6 in solid form, which solvent comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, or any combination thereof.

Example 3: A Reaction between LiF and PF.SUB.5 .Gas in the Presence of Perfluoroaromatic Solvent

[0091] LiF in solid form is dispersed in liquid hexafluorobenzene or a perfluoroaromatic liquid compound in the range C.sub.6F.sub.6 to C.sub.10F.sub.8.

[0092] The reaction that takes place is in accordance with reaction equation 1.

[0093] The reaction temperature range is 5 C. to 100 C.

[0094] The reaction pressure range is 0 kPa to 3 000 kPa, more preferably up to 1000 kPa.

[0095] Up to 99% recovery of LiPF.sub.6 may be achieved when produced LiPF.sub.6 is dissolved in a solvent for LiPF.sub.6 in solid form, which solvent comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, or any combination thereof.

Example 4: A Reaction between LiF and PF.SUB.5 .Gas in the Presence of Fluoroalkene Solvent

[0096] LiF in solid form is dispersed in liquid tetrafluoroethylene solvent (C.sub.2F.sub.4) or a liquid fluoroalkene compound selected from C.sub.3F.sub.6 or C.sub.4F.sub.8.

[0097] The reaction that takes place is in accordance with reaction equation 1.

[0098] The reaction temperature range is 94 C. to 100 C.

[0099] The reaction pressure range is 0 kPa to 3 000 kPa, more preferably up to 1000 kPa.

[0100] Up to 99% recovery of LiPF.sub.6 may be achieved when produced LiPF.sub.6 is dissolved in a solvent for LiPF.sub.6 in solid form, which solvent comprises ethylene carbonate, propylene carbonate, dimethyl carbonate, dimethyl ether, or any combination thereof.

Discussion

[0101] THE METHOD OF THE FIRST ASPECT OF THE INVENTION uses an inert, non-corrosive, non-poisonous liquid medium for the reaction of LiF and PF.sub.5 instead of corrosive HF which is the preferred liquid medium for this reaction in the art of the invention.

[0102] Thus, the inventors have eliminated the need to remove the HF from the product through tiresome purification processes such as vacuum distillation.

[0103] Furthermore, HF is known to be corrosive and reactive inside a battery, which makes its avoidance for use as a liquid medium all the more desirable.

[0104] Some advantages associated with the liquid media exploited by the method of the invention are the following: [0105] it is inert in relation to PF.sub.5 gas; [0106] it is inert in relation to the product LiPF.sub.6; [0107] it is often not poisonous; [0108] it dissolves the PF.sub.5 gas, making it readily accessible to the lithium fluoride without mass transfer limitations; [0109] no azeotropic formation of PF.sub.5 gas with the solvent is experienced, which tends to compete with lithium fluoride for PF.sub.5 gas in traditional HF involved processes; and [0110] the liquid media are non-corrosive.

[0111] Thus, the inventors have provided an attractive, utile and sustainable alternative for the production of LiPF.sub.6 which is particularly advantageous over prior art processes, some of which have been discussed herein.