United States Patent (19) 11 Patent Number: 5,993,767 Willmann Et Al

USOO5993767A United States Patent (19) 11 Patent Number: 5,993,767 Willmann et al. (45) Date of Patent: Nov.30, 1999

54). SOLVATE OF LITHIUM 5,378,445 1/1995 Salmon et al...... 423/301 HEXAFLUOROPHOSPHATE AND PYRIDINE, 5,616,636 4/1997 Avar et al...... 546/22 ITS PREPARATION AND PREPARATION FOREIGN PATENT DOCUMENTS PROCESS FOR LITHIUM HEXAFLUOROPHOSPHATE USING SAD 20 26 110 12/1970 Germany. SOLVATE OTHER PUBLICATIONS 75 Inventors: Patrick Willmann, Montgiscard; Chemical Abstracts, vol. 100, No. 21, 21 Mai 1984, Colum Régine Naejus, Tours; Robert bus, Ohio, US; abstract no 174608c, Mohamed, K. er at..: Coudert, Notre Dame D'Oe; Daniel “pyridinium poly (hydrogen fluoride)—a reagent for the Lemordant, Orsay, all of France preparation of hexafluorophosphates' XP002024671. 73 Assignee: Centre National D’Etudes Spatiales, Primary Examiner Wayne Langel France Attorney, Agent, or Firm-Burns, Doane, Swecker & Mathis, L.L.P. 21 Appl. No.: 09/000,232 57 ABSTRACT 22 PCT Filed: Jun. 18, 1997 The invention relates to a lithium hexafluorophosphate Sol 86 PCT No.: PCT/FR97/01097 Vate usable for the preparation of high purity lithium S371 Date: Jan. 23, 1998 hexafluorophosphate. S 102(e) Date: Jan. 23, 1998 This solvate of lithium hexafluorophosphate and pyridine 87 PCT Pub. No.: WO97/48709 complies with the formula: PCT Pub. Date: Dec. 24, 1997 30 Foreign Application Priority Data and is prepared by a proceSS comprising the following Stages: Jun. 19, 1996 FR France ...... 96 O7623 a) preparation of pyridinium hexafluorophosphate of for 511 Int. Cl.CI...... C01B 25/105/10; CO7D 213/20; mula CH-NHPF by the neutralization of hexafluoro CO7F 9/28 phosphoric acid HPF with pyridine and 52 U.S. Cl...... 423/301; 546/22; 546/347 b) conversion of the pyridinium hexafluorophosphate into 58 Field of Search ...... 423/301; 546/22, Solvate LiPF, CHN by exchange with a lithium 546/347 compound chosen from among lithium hydroxide, lithium alkoxides and alkyl-lithiums. 56) References Cited The LiPF can be regenerated from the Solvate by vacuum U.S. PATENT DOCUMENTS decomposition. 3,654,330 4/1972 Wiesboeck. 4,996,320 2/1991 Omemoto et al...... 546/22 14 Claims, 7 Drawing Sheets

% TRANSMISSION A

4.0

1633 U.S. Patent Nov.30, 1999 Sheet 1 of 7 5,993,767

U.S. Patent Nov.30, 1999 Sheet 2 of 7 5,993,767

% TRANSMSSION

673.09 557.71 O (cm1) 2OOO 16OO 1200 8OO 400 U.S. Patent Nov.30, 1999 Sheet 3 of 7 5,993,767

000€

009Z

000Z

000||

009

G/|0 09||'0 OGO’0 000’0 U.S. Patent Nov.30, 1999 Sheet 4 of 7 5,993,767

SN U.S. Patent Nov.30, 1999 Sheet 5 of 7 5,993,767

SN U.S. Patent Nov.30, 1999 Sheet 6 of 7 5,993,767

area 8 C w

007

99°888 008

OOZ|

OOOZ G’S 0"| U.S. Patent Nov.30, 1999 Sheet 7 of 7 5,993,767

als - S O Ye'

007 89°199 009 86°188

Z| 0|| 5,993,767 1 2 SOLVATE OF LITHIUM Thus, none of the presently known processes makes it HEXAFLUOROPHOSPHATE AND PYRIDINE, possible to prepare high purity lithium hexafluorophosphate ITS PREPARATION AND PREPARATION LiPF under easily implementable conditions and without PROCESS FOR LITHIUM using onerous reagents. HEXAFLUOROPHOSPHATE USING SAD DESCRIPTION OF THE INVENTION SOLVATE The present invention relates to the preparation of high DESCRIPTION purity LiPF by a simple, uncomplicated process using inexpensive, commercial products, with as the intermediate 1. Technical Field a Solvate of lithium hexafluorophosphate and pyridine. It The invention relates to a novel compound constituted by also relates to the Solvate and its preparation process. a Solvate of lithium hexafluorophosphate and pyridine uSable for the preparation of lithium hexafluorophosphate. The Solvate complies with the formula: It more particularly applies to the preparation of lithium Li(CHN)PF hexafluorophosphate used as an electrolyte in lithium 15 and has the advantage of being much easier to handle than carbon batteries. LiPF, because it is stable in air at ambient temperature, At present lithium batteries are being extensively devel whereas LiPF decomposes into PFs and LiF and must be oped for various applications, particularly in electric manipulated in a glove box. It also makes it possible to vehicles, portable equipments Such as portable telephones generate LiPF with a high purity level of 99.8% using and cameScopes, as well as in Space. These batteries use an Simple processes. electrolyte constituted by one or more organic Solvents According to the invention, this Solvate can be prepared containing in Solution a lithium Salt. Among the uSable by a process comprising the following Stages: lithium salts, lithium hexafluorophosphate (LiPF) is at a) preparation of pyridinium hexafluorophosphate of for present the most widely used, due to its high Solubility in mula CH-NHPF by neutralization of hexafluorophos organic Solvents, its conductivity and its Safety. 25 phoric acid HPF with pyridine using the stoichiomet 2. Prior Art ric quantity permitting the neutralization of only the The conventional method for the preparation of LiPF HPF and not the other acid impurities present in the consists of reacting PFs with LiF in anhydrous hydrofluoric Starting acid and acid, but the purity of LiPF prepared in this way is only 90 b) conversion of pyridinium hexafluorophosphate into to 95%, whereas purities of at least 99% are required for use Solvate LiPF, CHN by exchange with a lithium in a lithium battery in order to satisfy the LiPF storage compound chosen from among lithium hydroxide, Stability and Solubility requirements. lithium alkoxides and alkyl-lithiums. In this process, the first stage a) is easy to perform, In order to overcome this difficulty, it is still possible to because it can be carried out in an aqueous medium at obtain LiPF of higher purity by the process described in 35 ambient temperature from an inexpensive, commercial prod U.S. Pat. No. 3,654,330. According to this process, lithium uct (HPF in aqueous Solution). Moreover, through using the fluoride, anhydrous hydrofluoric acid and phosphorus pen precise Stoichiometric quantity corresponding to the neu tafluoride PFs are reacted to obtain impure LiPF, which is tralization of HPF and excluding other acid impurities then purified by reaction with acetonitrile. Thus, tetraaceto present in the Starting product, it is possible to obtain high nitrilolithium hexafluorophosphate Li(CHCN), PF is 40 purity pyridinium hexafluorophosphate, which will then lead produced, which then regenerates lithium hexafluorophoS to a high purity solvate Li(CHN)PF. phate by heating in a partial vacuum. It is also possible to This Stoichiometric quantity can be easily determined by directly produce Li(CHCN), PF by reacting PF in a carrying out before hand a neutralization test on the com Suspension of LiF in acetonitrile. mercial acid HPF used as the Starting product and moni This process makes it possible to obtain high purity 45 toring the neutralization by conductometry. lithium hexafluorophosphate, but it suffers from the disad It has in fact been found that HPF is stronger than the vantage of requiring the use of PF which is a very difficult other acids present as impurities in commercial Solutions product. and is neutralized first giving rise to a rapid conductivity Another way for obtaining alkali metal hexafluorophoS drop of the solution. The end of this drop corresponds to the phates has been investigated by Syed Mohamed et al in J. 50 complete neutralization of HPF and it is thus possible to Fluorine Chem., 23, 1983, pp 509-514. According to this determine the basic Stoichiometric quantity necessary for document, the Starting product is pyridinium hexafluoro this neutralization. phosphate CH-NHPF, which is then treated with an This method for preparing CH-NHPF is much easier to ammonium or alkali metal hydroxide in an aqueous implement than that described by Syed Mohamed in J. medium, but this process has not made it possible to isolate 55 Fluorine Chem., 23, 1983, pp 509-514, where said pyri solid LiPF from said medium. Moreover, the preparation of dinium hexafluorophosphate is obtained by a two-stage the starting product CH-NHPF involves a low temperature reaction, firstly preparing a poly(hydrogen fluoride)- reaction (-80 C.) between the pyridine and the anhydrous pyridinium reagent at a temperature of -80 C., followed by hydrofluoric acid, followed by the reaction of the product the reaction of Said reagent with dropwise added phosphoryl obtained with phosphoryl chloride. This involves difficult 60 chloride. performance using expensive reagents (POCL), which is The first stage of the proceSS according to the invention is difficult to carry out on an industrial Scale. easier to perform, because it is carried out in an aqueous Lange et al in BER. 63B, 1058–70, 1930 describe the Solution at ambient temperature. It also makes use of uncom preparation of CH3NHPF by reacting pyridine in acetic plicated reagents, which are commercially available, Such as acid with ammonium hexafluorophosphate. However, they 65 HPF solutions in water. did not envisage using this pyridinium hexafluorophosphate In the Second stage b) of the process according to the for preparing lithium hexafluorophosphate. invention, the pyridinium hexafluorophosphate is converted 5,993,767 3 4 into Solvate Li(C5H5N)PF by exchange with a lithium illustrative and non-limitative manner, with reference to the compound. This Solvate has the major advantage of being, attached drawings. unlike LiPF, Stable at ambient temperature, permitting easier handling and Storage. BRIEF DESCRIPTION OF THE DRAWINGS According to a first embodiment of Said Stage, the lithium compound used is hydrated or unhydrated lithium FIG. 1 is a graph illustrating the conductometric dosage hydroxide, in an alcoholic medium, e.g. methanol or etha curve of commercial hexafluorophosphoric acid by lithium nol. This reaction is fast and the Solvate is obtained in hydroxide. solution in alcohol. It can then be obtained in Solid form by FIG. 2 shows the infrared spectrum of pyridinium evaporating the alcohol. hexafluorophosphate. According to a Second embodiment of conversion Stage FIG. 3 shows the Raman spectrum of pyridinium b), the lithium compound used is a lithium alkoxide and the hexafluorophosphate. eXchange reaction takes place in the alcohol corresponding to lithium alkoxide. FIG. 4 illustrates the NMR spectrum of the pyridinium In this case, it is possible to directly prepare the alkoxide hexafluorophosphate proton. in an alcoholic medium by dissolving lithium in an alcohol 15 FIG. 5 shows the NMR spectrum of the proton of the CXCCSS. solvate Li(CHN)PF. This reaction can also be performed in an aprotic medium, e.g. in tetrahydrofuran, other ethers or acetonitrile. This FIG. 6 shows the infrared spectrum of lithium hexafluo gives the Solvent, as previously, by evaporation of the rophosphate obtained by the process of the invention. reaction medium constituted by the alcohol or aprotic Sol FIG. 7, for comparison purposes, shows the infrared Vent. Spectrum of the commercial lithium hexafluorophosphate. According to a third embodiment of stage b), the lithium compound used is an alkyl-lithium and the exchange reac DETAILED DESCRIPTION OF EMBODIMENTS tion takes place in a Saturated aliphatic hydrocarbon, Such as The following examples illustrate the preparation of hexane or pentane. The alkyl-lithiums which can be used are 25 lithium hexafluorophosphate by the processes according to n-butyl lithium and tert. butyl lithium. In this case, the the invention. Solvate precipitates in the reaction medium and can be recovered by filtration. EXAMPLE 1. The invention also relates to a process for the preparation of lithium hexafluorophosphate from the solvate of lithium Preparation of Pyridinium Hexafluorophosphate hexafluorophosphate and pyridine of formula: (CHNHPF) In this example, the Starting product is commercial, aqueous solution of hexafluorophosphoric acid HPF, which According to this process, Said Solvate undergoes a vacuum is a mixture of the Strong acid HPF and weak acids. decomposition at a temperature equal to or below 50° C. in 35 Firstly a determination takes place of the Stoichiometric order to eliminate the pyridine by volatilization. quantity necessary for Solely converting the Strong acid This decomposition can be performed under dynamic HPF of said commercial solution into pyridinium hexafluo Vacuum, under a pressure below 1 Pa, at a temperature equal rophosphate. This is brought about by neutralizing Said to or below 50° C. in order to avoid LiPF decomposition. solution, which contains 0.196 g of HPF for 20 cm of According to a performance variant of this process, the 40 water, by 0.98 N lithium hydroxide and following or moni Solvate is reacted with concentrated Sulphuric acid in order toring the neutralization by conductometry. to eliminate the pyridine by precipitation in the form of pyridinium Sulphate. FIG. 1 shows the curve obtained under these conditions, In order to carry out this reaction, the Solvate is dissolved namely the evolution of the conductivity (in mS. cm) of in an aprotic Solvent, in which the pyridinium Sulphate is 45 the solution, as a function of the added lithium hydroxide insoluble, whereas the LiPF is soluble therein. However, it volume (in cm). is necessary to avoid the addition of a HSO excess in order It can be seen that the first Section of the conductometry to avoid a lithium Sulphate coprecipitation. The aprotic curve is linear and corresponds up to the Volume V to the Solvent can be tetrahydrofuran. neutralization of HPF. As from V and up to the volume V, The Solvate used as the Starting product is advantageously 50 the lithium hydroxide addition does not modify the conduc prepared by the processes described hereinbefore. tivity of the solution. This corresponds to the neutralization This lithium hexafluorophosphate preparation procedure of the weaker acid impurities. Beyond V2, the conductivity is particularly interesting, because the Starting product, the of the Solution increases linearly, because the neutralization Solvate of Li(CHN)PF, can be prepared with a high of the acids is ended. degree of purity. Thus, from Said Solvate is obtained very 55 This determines the basic quantity corresponding to the pure lithium hexafluorophosphate using easily performable Volume V making it possible to neutralize Solely the Strong processes. In addition, the preparation of, the Solvate by the acid HPF. This quantity corresponds to 10.5 cm of 0.098 processes described hereinbefore is easy to implement. N lithium hydroxide for 20 cm of commercial aqueous Thus, it is possible to obtain high purity LiPF at a cost solution containing 0.196 g of HPF. On the basis of these lower than existing LiPF. 60 results, pyridinium hexafluorophosphate is prepared using Finally, in view of the fact that the Solvate is stable at the same commercial hexafluorophosphoric acid batch and ambient temperature the LiPF handling and Storage prob working in the following way. lems are obviated, because it can be regenerated from the Dropwise addition takes place of 7.2 cm of pyridine to 20 Solvate only, when this is necessary for preparing LiPF g of aqueous commercial HPF, Solution (Fluka product based electrolyte. 65 having a 65% HPF content) placed in ice. Pyridinium Other features and advantages of the invention can be hexafluorophosphate precipitation is immediate and the lat gathered from reading the following description given in an ter is separated by filtration. This is followed by three 5,993,767 S 6 recrystallizations in water and then one in absolute FIG. 5 shows the NMR spectrum of the proton of this methanol, followed finally by one in absolute ethanol. This Solvate. It is possible to see that the Singlet at 11.68 ppm is gives 11.3 g of pyridinium hexafluorophosphate, which absent, whereas it would appear on the Spectrum of FIG. 4 corresponds to a total yield of 49%. The product is then corresponding to the product CH-NHPF of example 2. treated in the oven at 110° C. up to constant weight. The percentage analysis of the Solvate is given in the FIG. 2 shows the infrared spectrum of the product following table 2. obtained. It is possible to see the two characteristic bands of PF, at 557.71 (558) and 832.35 (832) with a shoulder at TABLE 2 890 cm. The other bands are attributed to the pyridinium Percentage composition nucleus, including that at 1642 cm, which can be confused 1O with that between 1630 and 1645 cm, which occurs in all the IR spectra of LIPF and which is without doubt a Example 2 22.61 49.41 12.70 3.90 harmonic of the band at 832 cm. Example 3 22.OO 4937 12.85 3.50 Thus, the infrared spectrum of the product has bands Calculated 26.OO 49.34 13.41 3.00 identical to those described by Syed Mohamed et al in J. 15 Fluorine Chem., 23, 1983, pp 509-514 and in Spectro chimica Acta, 41A(5), 1985, pp 725-728. EXAMPLE 3 FIG.3 shows the Raman spectrum of the product obtained Preparation of the Solvate LiPF, Pyridine and it is possible to see thereon the band at 1008.6 cm', This example follows the operating procedure of example which corresponds to N-H". 2, but using absolute methanol as the reaction medium. In FIG. 4 shows the NMR spectrum of the proton. On this this case, 0.84 g of LIOH, HO in powder form is added to spectrum the widened singlet at 11.68 ppm (11.7 ppm) 4.5g of CH-NHPF obtained in example 1 in 100 cm of corresponds to N-H". absolute methanol. AS previously, the reaction is fast and The percentage analysis of the product obtained is given 25 Solubilization complete. The methanol is then evaporated in the following table 1: after adding 40 cm anhydrous benzene and eliminating under a partial vacuum the benzene-methanol-water ternary azeotrope. This gives 2.9 g of Solid product, which is the TABLE 1. Solvate LiPF, pyridine. C% N% F% P% The characteristics of this product are identical to those of the product obtained in example 2. The percentage analysis Obtained 26.67 6.11 45.90 13.50 Calculated 26.68 6.22 50.64 13.76 is given in table 2. In table 2, the values found for Li, higher than the calculated percentage, are explained by the fact that during The purity check carried out in accordance with the principle the elimination of the alcohols under a partial vacuum, a adopted by Syed Mohamed et al using lithium hydroxide in 35 fraction of the complex may have been destroyed in accor place of Soda revealed that the Salt had a degree of purity of dance with Li(CHN)PF->CHN (vacuum entrained)+ 99.8%. LiPF. A further consequence is a drop in its carbon per It is possible to improve by at least 20% the CH-NHPF Centage. yield of this example by performing only one recrystalliza This result is compatible with the analysis of lithium by tion in water and one in absolute methanol, because the 40 atomic absorption, because 2.33 and 2.48 ppm were found, infrared spectrum of the product obtained is the same as that respectively for examples 2 and 3, whereas the theoretical obtained after all the aforementioned recrystallizations. value would be 1.98 ppm for Li in the pure complex and 3.01 EXAMPLE 2 ppm for Li in LiPF. Preparation of the Solvate LiPF, Pyridine 45 EXAMPLE 4 In this example, the pyridinium hexafluorophosphate Preparation of the Solvate LiPF, Pyridine obtained in example 1, is transformed into Solvate LiPF, In this example the Starting product is the pyridinium pyridine, by reaction with lithium hydroxide in an absolute hexafluorophosphate obtained in example 1 and it is con ethanol medium. 50 verted into Solvate by exchange with a lithium alkoxide To this end, 0.42 g (10° mole) of commercial lithium constituted by lithium methanolate. hydroxide (LiOH, H2O) is added to 2.25 g (10f mole) of The lithium methanolate is firstly prepared from a piece of pyridinium hexafluorophosphate CH-NHPF obtained in metallic lithium placed in a bottle previously calibrated example 1, Suspended in 50 cm of absolute ethanol, in under dry argon. To this bottle are added 50 cm of methanol which the salt is only slightly soluble. The reaction is fast 55 for 2.2.10 mole of lithium. As soon as the alkoxide has and solubilization complete. This is followed by the addition formed, the equivalent Stoichiometric quantity of pyridinium of 20 cm of anhydrous benzene, so as to eliminate under hexafluorophosphate obtained in example 1 is Suspended in partial vacuum the ternary benzene-ethanol-water azeo the bottle. The reaction is fast, the final mixture being free trope. This gives 2.1 g of Solid product, which is the Solvate from water. The Solvate is obtained by evaporating the LiPF, pyridine, which corresponds to a 91% yield. 60 Solvent without adding anhydrous benzene. After evapora The infrared and Raman spectra of this product tion under partial vacuum at 30° C., the Solvate LiPF, LiPFCHN are identical to those of the CH-NHPF pyridine is obtained in a quasi-quantitative form. obtained in example 1. Thus, N-H and N-Li both give the band at approximately 1008 cm in Raman spectrom EXAMPLE 5 etry and only the pyridines solvated by HO are towards 65 Preparation of the Solvate LiPF, Pyridine 1026 cm. In infrared, the NH band passes to 3300 cm, This example follows the operating procedure of example which belongs to an unusable range of the Spectrum. 4, but as the lithium alkoxide use is made of lithium 5,993,767 7 8 ethanolate, which is prepared in the Same way by adding FIG. 7 shows for comparison purposes the infrared spec ethanol to a bottle containing a piece of lithium. The Solvate trum of the commercial Aldrich product LiPF. This spec LiPF, pyridine is also obtained in a quasi-quantitative form. trum reveals the same bands at 832 (890) and 561 cm. EXAMPLE 6 EXAMPLE 10 Preparation of Solvate LiPF, Pyridine Preparation of LiPF, Pyridine In this example, LiPF is prepared from the solvate LiPF, In this example, the Salt obtained in example 1 is con pyridine obtained in example 8 Separating the pyridine by verted into Solvate using butyl-lithium as the lithium com precipitation in pyridinium Sulphate form. To this end, to the pound. 8.10 mole of CH-NHPF obtained in example 1 solution of the Solvate in THF obtained in example 8 is are suspended in 5 cm of 1.6 Mbutyl-lithium solution in added concentrated Sulphuric acid (96%), which leads to the hexane (Aldrich Solution) under argon. At ambient precipitation of the pyridinium Sulphate. The Solution is then temperature, the reaction evolves in about 20 hours and a filtered to eliminate the precipitate, followed by the vacuum total Solvate precipitation is obtained. The Solvate is recov evaporation of the organic Solvent at a temperature below ered by filtration and is then washed with CH-Cl. 15 50° C. Thus, LiPF is very rapidly obtained. The Solvate obtained has the same characteristics as that We claim: obtained in the previous examples. 1. Solvate of lithium hexafluorophosphate and pyridine of formula: EXAMPLE 7 Preparation of the Solvate LiPF, Pyridine 2. Process for the preparation of the Solvate of lithium This example follows the same operating procedure as in hexafluorophosphate and pyridine of formula: example 6, but tert. butyl lithium is used as the lithium compound. In small portions 8.5 10 mole of C5H5NHPF obtained in example 1 are added to 5 cm of a 1.7M. tert. 25 characterized in that it comprises the following Stages: butyl lithium Solution in pentane (Aldrich Solution) kept at a) preparation of pyridinium hexafluorophosphate of for -20 C. The reaction is fast and highly exothermic, which mula CH-NHPF by neutralization of hexafluorophos leads to the boiling of the pentane. The product precipitates phoric acid HPF with pyridine using the stoichiomet as in example 6 and it is recovered by filtration, followed by ric quantity permitting the neutralization of only the washing with CHCl2, as previously. HPF and not the other acid impurities present in the The characteristics of the product obtained are identical to Starting acid and those obtained with the preceding examples. b) conversion of the pyridinium hexafluorophosphate into EXAMPLE 8 Solvate Li(CHN)PF by exchange with a lithium 35 compound Selected from the group consisting of Preparation of the Solvate LiPF, Pyridine lithium hydroxide, lithium alkoxides and alkyl lithiums. In this example, the pyridinium Salt obtained in example 3. ProceSS according to claim 2, characterized in that in 1 is converted into Solvate using lithium methanolate in an Stage b) use is made of hydrated or unhydrated lithium aprotic medium as the lithium compound. In this case, 1.26 40 hydroxide and the exchange reaction is performed in an 10° mole of lithium are reacted with 20 cm of absolute alcoholic medium. methanol to form lithium methanolate, as in example 4. 4. Process according to claim 3, characterized in that the After evaporating the methanol, the dry residue is Suspended alcohol is methanol or ethanol. in 20 cm of tetrahydrofuran (THF). Preparation also takes 5. ProceSS according to claim 2, characterized in that in place of a suspension of the salt CH-NHPF obtained in 45 Stage b) use is made of a lithium alkoxide and the exchange example 1 suspending 2.85g of said salt in 40 cm of THF. reaction is performed in the alcohol corresponding to lithium The two Suspensions are then mixed. The reaction is fast and alkoxide or in an aprotic medium. there is a total Solubilization of the Solvate. The Solvate is 6. Process according to claim 5, characterized in that the then isolated by eliminating THF by partial vacuum evapo lithium alkoxide is lithium methanolate or ethanolate. ration at ambient temperature. The product obtained has the 50 7. Process according to claim 6, characterized in that the Same characteristics as that obtained in the preceding aprotic medium is tetrahydrofuran. examples. 8. Process according to claim 5, characterized in that the aprotic medium is tetrahydrofuran. EXAMPLE 9 9. Process according to claim 2, characterized in that in Preparation of LiPF 55 Stage b) use is made of an alkyl-lithium and the exchange reaction is performed in a Saturated aliphatic hydrocarbon. In this example, LiPF is prepared by vacuum decompo 10. Process according to claim 9, characterized in that the Sition of the Solvate obtained in example 2, working under alkyl-lithium is butyl lithium or tert. butyl lithium. a dynamic vacuum at a pressure below 1 Pa and a tempera 11. Process for the preparation of lithium hexafluorophos ture of 50° C., pure LiPF is directly obtained. 60 phate LiPF characterized in that it consists of Subjecting FIG. 6 shows the infrared spectrum of the product the Solvate of lithium hexafluorophosphate and pyridine of obtained under these conditions and which corresponds to formula: LiPF. Thus, the bands are at u(P-F)=832 cm with a shoulder at 888 cm and 8(P-F) at 559 cm. The finally regenerated LiPF purity, estimated by Li 65 to a vacuum decomposition at a temperature equal to or dosing in atomic absorption is close to 99% (98.7 and below 50° C. in order to eliminate the pyridine by volatil 98.9%). ization. 5,993,767 9 10 12. Process according to claim 11, characterized in that reacted with Sulphuric acid to eliminate the pyridine by the Solvate is prepared by a process comprising the follow precipitation in the form of pyridinium Sulphate. ing Stages: 14. Process according to claim 13, characterized in that a) preparation of pyridinium hexafluorophosphate of for the Solvate is prepared by a process comprising the follow 5 ing Stages: mula CH-NHPF by neutralization of hexafluorophos a) preparation of pyridinium hexafluorophosphate of for phoric acid HPF with pyridine using the stoichiomet mula CH-NHPF by neutralization of hexafluorophos ric quantity permitting the neutralization of only HPF phoric acid HPF with pyridine using the stoichiomet and not the other acid impurities present in the Starting ric quantity permitting the neutralization of only HPF acid and and not the other acid impurities present in the Starting b) conversion of the pyridinium hexafluorophosphate into acid and Solvate Li(CHN)PF by exchange with a lithium b) conversion of the pyridinium hexafluorophosphate into compound Selected from the group consisting of Solvate Li(CHN)PF by exchange with a lithium lithium hydroxide, lithium alkoxides and alkyl compound Selected from the group consisting of lithiums. lithium hydroxide, lithium alkoxides and alkyl 13. Process for the preparation of lithium hexafluorophos 15 lithiums. phate LiPF, characterized in that the Solvate of lithium hexafluoride and pyridine of formula Li(CHN)PF is