Preparation of Lithium Hexafluorophosphate Solutions Herstellung Von Lithiumhexafluorphosphatlosungen Preparation De Solutions D'hexafluorophosphate De Lithium

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) int. CI.6: C01 B 25/10, H01M6/14, of the grant of the patent: C01 D 1 5/00, H01 M 6/1 6, 31.03.1999 Buiietin 1999/13 H01M 10/40 (21) Application number: 94926652.2 (86) International application number: (22) Date of filing: 02.09.1994 PCT/US94/09843

(87) International publication number: WO 95/17346 (29.06.1995 Gazette 1995/27)

(54) PREPARATION OF LITHIUM HEXAFLUOROPHOSPHATE SOLUTIONS HERSTELLUNG VON LITHIUMHEXAFLUORPHOSPHATLOSUNGEN PREPARATION DE SOLUTIONS D'HEXAFLUOROPHOSPHATE DE LITHIUM

(84) Designated Contracting States: • BARNETT, Rebecca, A. DE FR Maiden, NC 28650 (US)

(30) Priority: 23.12.1993 US 172690 (74) Representative: McCall, John Douglas et al (43) Date of publication of application: WP. THOMPSON & CO. 09.10.1996 Bulletin 1996/41 Coopers Building Church Street (73) Proprietor: FMC CORPORATION Liverpool L1 3AB (GB) Philadelphia, PA 19103 (US) (56) References cited: (72) Inventors: EP-A- 0 643 433 US-A- 3 654 330 • SALMON, Dennis, J. US-A-4 880 714 Gastonia, NC 28054 (US) • BARNETTE, D. Wayne • PATENT ABSTRACTS OF JAPAN vol. 008, no. Bessemer City, NC 28016 (US) 142 (E-254), 3 July 1984 & JP-A-59 051475 (SANYO DENKI KK), 24 March 1984,

CO CO CO <7> IO CO Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in o a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. Q_ 99(1) European Patent Convention). LU Printed by Xerox (UK) Business Services 2.16.7/3.6 1 EP 0 735 983 B1 2

Description cation difficult. One preparation method reacts lithium hydride (LiH) and phosphorus pentachloride (PCI5) in [0001] This invention concerns a manufacturing the presence of hydrofluoric acid anhydride. The proc- method for high purity, battery quality, lithium hexaf luor- ess starts with solid PCI5 which always contains some ophosphate and high purity, lithium hexafluorophos- s moisture, sulfate ions, iron and lead which impurities phate solutions suitable for use in high energy batteries. contaminate the electrolyte; unfortunately even rela- [0002] The high voltages of primary lithium batteries tively small amounts of these impurities are unaccepta- and the charging voltage for secondary lithium battery ble in electrolytes. Another method reacts a lithium designs place a demanding requirement on the electro- halide and PF6 in hydrofluoric acid anhydride, this proc- lyte salt chosen for these battery applications. The salt 10 ess, employing the solid gas reaction of porous LiF-HF must have sufficient electrochemical stability to avoid with PF6 gas, avoids the moisture problems of earlier reduction reactions, sufficient chemical stability to avoid processes; however high purity PF5 gas is extremely reaction with the other battery components and suffi- expensive. The process of published Japanese pub- cient solubility in the electrolyte solvent (or polymeric lished application Hei 4-175216 (1992) claims to over- matrix) to allow sufficient conductivity for the discharge 15 come the high PF5 costs by reacting PCI5 and of primary batteries and for the charging of secondary hydrofluoric acid at -20 °C or lower and an HF solution, batteries. HPF6, is formed. This resultant reaction solution is [0003] Lithium hexafluorophosphate meets the elec- warmed up to -10 °C to 20 °C to produce high purity PF5 trochemical and conductivity requirements for many gas. The PF5 gas is introduced carefully into a solution battery applications. However, the salt is chemically 20 of LiF-HF to produce LiPF6 at -30 °C. The LiPF6 precip- very reactive and difficult to manufacture and purify. The itates as 2-3 mm particles which are recovered using use of this salt as the electrolyte salt in a lithium battery usual methods of recovery. A process is known in which can lead to reactions with other battery components NH4PF6 is reacted with LiBr in dimethoxyethane (DME) and thermal decomposition of the salt. Lithium hex- to form a LiPF6 • DME complex. The product has high afluorophosphate prepared from aqueous solutions of 25 purity but the DME is very difficult to remove which limits hexaf luorophosphoric acid and a basic lithium salt, such the product to uses where the DME can be tolerated. as lithium hydroxide or lithium carbonate, can hydrolyze [0006] Processing to avoid contamination by acidic to form three anions P02F2-, HPO3F", and P04. Thus, components has been described. US Patent 4,880,714 the precipitated lithium hexafluorophosphate salt pre- discloses the reaction of a salt with a cation containing pared from aqueous solutions will contain these unde- 30 an adduct of a proton and a Lewis base and an anion sirable contaminants. These hydrolysis reactions will consisting of hexafluorophosphate in an ether with a yield acids which catalyzes the hydrolysis reaction. The lithium base to form a solution from which the LiPF6- poor thermal stability of lithium hexafluorophosphate ether complex can be isolated. Due to difficulties in makes removal of water, in order to produce anhydrous removing the ether from the complex, the complex must lithium hexafluorophosphate, extremely difficult. Conse- 35 be incorporated directly into the battery electrolyte and, quently lithium hexafluorophosphate prepared by aque- thus, this product is not useful for battery designs not ous routes are generally unsuitable for battery containing the ether. applications. The potential exists for acid catalyzed [0007] The reaction of potassium hexafluorophos- decomposition reactions with other solvents. phate with lithium bromide in acetonitrile is described to [0004] To avoid the problems of dealing with hydroly- 40 yield a potassium bromide precipitate, which is filtered, sis of the hexafluorophosphate anion in aqueous solu- and a solution of lithium hexafluorophosphate in ace- tions, processes were developed whereby lithium tonitrile recovered. Removal of acetonitrile, extraction hexafluorophosphate was produced by reactions of sus- by a halogenated hydrocarbon solvent, and filtration of pended lithium fluoride and gaseous phosphorous pen- impurities yields a solution from which crystalline tafluoride in organic solvents. The difficulties of these 45 [Li(CH3CN)4 PF6] can be isolated by removal of the processing methods include handling extremely reac- organic solvent. This product is limited to battery appli- tive, expensive phosphorous pentaf luoride gas and diffi- cations containing acetonitrile as an electrolyte compo- cult isolation of the non-solvated salt from the organic nent and is not generally suitable for batteries. solution. The reaction of lithium halides with phospho- [0008] The present invention provides a process rous pentafluoride in anhydrous hydrofluoric acid sol- so which overcomes the problems for producing battery vent has been described. Descriptions of further quality lithium hexafluorophosphate solutions by react- processing to reduce cost and increase purity are ing, under basic conditions, lithium salts with alkali revealed. These procedures leave a residual hydrofluo- metal or ammonium or organoammonium salts of hex- ric acid contained in the solid product which cannot be af luorophosphoric acid in a non-protic organic solvent in completely removed and may be detrimental to battery 55 a reaction zone that is continuously saturated with a performance. compound selected from anhydrous ammonia, methyl [0005] Lithium hexafluorophosphate is extremely amine or ethyl amine. In particular embodiments of this hygroscopic which has made its manufacture and purifi- invention, ammonia or other volatile amines are added

2 3 EP 0 735 983 B1 4 to increase the rate of the reaction as well as to precipi- more to complete. Ammonia is added at a rate to pro- tate acidic contaminants from the reactant hexafluoro- vide continuous saturation of the atmosphere in the phosphate salt. A variety of organic solvents can be reaction zone with ammonia. The reaction zone may be used in the processing, and in preferred embodiments constructed of any convent material inert to the reac- low boiling organic solvents are used so that the initial 5 tants and products. solvent can be removed in the presence of another [0013] The reactants, LiCI and KPF6 are employed in higher boiling solvent to prepare the final battery elec- substantially stoichiometric amounts with a slight trolyte solutions. The advantages of this process excess of LiCI generally being employed. Anhydrous include avoidance of acidic conditions which can yield ammonia is used in substantial amounts as it is desira- undesired decomposition reactions and avoidance of w ble to keep the reaction solution saturated with ammo- the thermally unstable solid salt; for example, by satu- nia. Stopping the ammonia addition apparently stops rating the reaction solution with anhydrous ammonia. the reaction. The reaction is ordinarily done under ambi- The reaction is optionally, beneficially conducted in the ent pressure and temperature conditions. Reaction presence of an amine which can be easily removed under pressure can be done; the reaction is best con- when the reaction is completed; for example by use of 75 ducted in an ammonia saturated atmosphere. Addition methyl or ethyl amine. of the ammonia causes a small exotherm, otherwise the [0009] A variety of reactant lithium salts useful in prac- reaction is done under ambient temperature and pres- ticing this invention include but are not limited to lithium sure conditions. Ammonia advantageously is added chloride, lithium bromide, lithium perchlorate, lithium throughout the reaction period. tetrafluoroborate, lithium nitrate, lithium acetate, lithium 20 [0014] Battery quality electrolytes based on LiPF6 dis- benzoate and the like. Choice is usually governed by solved in organic solvents are useful battery electro- solubility of the by-product salt formed from the cation of lytes. The use of NH3 permits use to lithium chloride the hexafluorophosphate salt and the anion of the lith- (LiCI); without the presence of NH3 the KPF6-LiCI reac- ium salt. The lithium salt must also have sufficient solution does not proceed. Ammonia dissolves the LiPF6 bility to allow the reaction to proceed. In a similar 25 product and shifts the reaction to completion. Lithium fashion, the choice of cation in the reactant hexafluoro- bromide (LiBr) can be used in place of LiCI but this phosphate salt is generally governed by the solubility of results in KBr being dissolved in the solvent. LiCI is not the resultant by-product salt. so soluble in the solvents so the product LiPF6 is purer. [0010] Salts of hexaf luorophosphorc acid useful in After completion of the reaction, NH3 is removed from practicing this invention include, but are not limited to, 30 the reaction zone or mixture as a gas. Thus, NH3 is pre- potassium hexafluorophosphate, sodium hexafluoro- ferred over amines because neither NH3 or amines are phosphate, ammonium hexafluorophosphate and orga- wanted in the electrolyte. The reaction mixture is recov- noammonium hexafluorophosphate compounds of the ered by ordinary means such as filtering off by-products formula R4NPF6 wherein R is selected from alkyl and vacuum removal of the ammonia. groups of 1 to 8, preferably 1 to 4, carbon atoms and 35 [0015] The following examples further illustrate the aryl groups of 6 to 12 carbon atoms. invention. [001 1 ] Solvents useful in practicing this invention are low-boiling non-protic organic solvents having low solu- Example 1 . LiPF6 in Propylene Carbonate bility of the sodium, potassium, ammonium, or organo ammonium salt containing the anion of the reactant Nth- 40 [0016] ium salt and high solubility of the lithium hexafluorophosphate, which include, but are not limited to, Solution A: 553g recrystallized KPF6 was dissolved acetonitrile, dimethylcarbonate, diethylcarbonate, meth- in 3000cc CH3CN at room temperature. ylene chloride and dimethoxyethane or other low boiling Solution B: 127g LiCI was added to 400cc CH3CN non-protic solvents. These low boiling solvents can be 45 at room temperature. mixed with high viscosity solvents such as ethylene carbonate or propylene carbonate, after which the low boil- [0017] Solution A was added to solution B at room ing solvent is removed. The viscosity of these materials temperature. Ammonia was then sparged into mixture when dissolved in a high viscosity solvent may be mod- for 24 hours. Solution was filter to remove KCI. Solution ified (see draft) such as dimethyl carbonate or diethyl- so was mixed with propylene carbonate and the ace- carbonate. The last few percent of the reaction solvent tonitrile was removed by evaporation. Product con- is difficult to remove from the hexafluorophosphate tained 0.1% KCI. product and a wiped film distillation apparatus has been found useful for removing the acetonitrile. Comparison Example A. [001 2] The reaction as generally conducted at room 55 temperature or slightly above. High temperatures are [0018] Example 1 was repeated without the ammonia avoided to avoid decomposing the hexafluorophosphate sparge. No reaction occurred. salts. The reaction is slow and may take 24 hours or

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Example 2. LiPF6 in Mixed Solvents. 6. The process of claim 1 further characterized by recovering the lithium hexafluorophosphate from [0019] Example 1 was repeated. Following evapora- the solution by filtering the original product solution, tive removal of CH3CN a second solvent is added to the adding a higher boiling solvent, selected from ethyl- UPF6/PC solution. The second solvent could be s ene carbonate or propylene carbonate, to the initial dimethylcarbonate, diethylcarbonate, ethylene carbon- product solution of lithium hexafluorophosphate ate. and removing the initial low boiling solvent and ammonia or amine by heating under vacuum. Example 3. LiPF6 in PC using LiBr. 10 7. A process for preparing solutions of lithium hex- [0020] Example 1 was repeated substituting LiBr for afluorophosphate characterized by reacting, under LiCI. The result was a product containing 3% KBr. basic conditions, potassium, hexafluorophosphate salt with lithium chloride in acetonitrile to produce a Example 4. LiPF6 in PC. solution of lithium hexafluorophosphate and precip- 15 itated potassium chloride while keeping the solution [0021] Example 1 was repeated substituting LiBr for basic by saturating the solution with anhydrous LiCI and without the ammonia sparge. The resulting ammonia. product was discolored due to acid-catalyzed decomposition. 8. The process of claim 7 further characterized by 20 recovering the lithium hexafluorophosphate from Claims the solution by filtering the original product solution, adding a higher boiling solvent, selected from ethyl- 1. A process for preparing solutions of lithium hex- ene carbonate or propylene carbonate, to the initial afluorophosphate characterized by reacting, under product solution of lithium hexafluorophosphate basic conditions, a lithium salt with a salt selected 25 and removing the initial low boiling solvent and from sodium, potassium, ammonium, or tetraalkyl ammonia or amine by heating under vacuum. ammonium hexafluorophosphate in a low boiling, non-protic organic solvent in a reaction zone that is Patentanspruche continuously saturated with a compound selected from anhydrous ammonia, methyl amine or ethyl 30 1. Verfahren zur Herstellung von Losungen aus Lithi- amine to produce a solution of lithium hexafluoro- umhexafluorophosphat, gekennzeichnet durch das phosphate and a precipitated sodium, potassium, zur Reaktion bringen, unter basischen Bedingun- ammonium, or organo ammonium salt containing gen, eines Lithiumsalzes mit einem Salz, das aus the anion of the reactant lithium salt. Natrium-, Kalium-, Ammonium- oder Tetraalkylam- 35 moniumhexafluorophosphat ausgewahlt wird, in 2. The process of claim 1 characterized in that the einem niedrigsiedenden, nichtprotogenen organi- organic solvent is selected from acetonitrile, schen Losungsmittel in einer Reaktionszone, die dimethylcarbonate, diethylcarbonate, dimethox- kontinuierlich mit einer Verbindung gesattigt wird, yethane and methylene chloride. die aus wasserfreiem Ammoniak, Methylamin oder 40 Ethylamin ausgewahlt wird, zur Herstellung einer 3. The process of claim 1 characterized in that the Losung aus Lithiumhexafluorophosphat und einem reactant lithium salt is selected from lithium chlo- prazipitierten Natrium-, Kalium-, Ammonium- oder ride, lithium bromide, lithium perchlorate, lithium Organoammoniumsalz, welches das Anion des nitrate, lithium acetate, lithium tetrafluoroborate or Reaktionspartners Lithiumsalz enthalt. lithium benzoate. 45 2. Verfahren nach Anspruch 1, dadurch gekenn- 4. The process of claim 1 characterized in that the zeichnet, daB das organische Losungsmittel aus reactant organohexafluorophosphate salt is a Acetonitril, Dimethylcarbonat, Diethylcarbonat, tetraalkyl ammonium hexafluorophosphate of the Dimethoxyethan und Methylenchlorid ausgewahlt formula R4NPF6 wherein R is selected from alkyl so wird. groups of 1 to 8 carbon atoms. 3. Verfahren nach Anspruch 1, dadurch gekenn- 5. The process of claim 1 characterized in that the zeichnet, daB der Reaktionspartner Lithiumsalz basic conditions are achieved by means selected aus Lithiumchlorid, Lithiumbromid, Lithiumperchlo- from adding an effective amount of an amine or sat- 55 rat, Lithiumnitrat, Lithiumacetat, Lithiumtetrafluoro- urating the reaction solution with anhydrous ammo- borat oder Lithiumbenzoat ausgewahlt wird. nia. 4. Verfahren nach Anspruch 1, dadurch gekenn-

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zeichnet, daB der Reaktionspartner Organohe- mine pour produire une solution d'hexafluorophos- xafluorophosphatsalz ein phate de lithium et un precipite de sel de sodium, Tetraalkylammoniumhexafluorophosphat der For- de potassium, d'ammonium ou d'ammonium orga- mel R4NPF6 ist, worin R aus Alkylgruppen von 1 nique contenant I'anion du sel de lithium reactant. Kohlenstoffatom bis 8 Kohlenstoffatomen ausge- 5 wahlt wird. 2. Le procede de la revendication 1 , caracterise en ce que le solvant organique est selectionne parmi 5. Verfahren nach Anspruch 1, dadurch gekenn- I'acetonitrile, le dimethylcarbonate, le diethylcarbo- zeichnet, daB die basischen Bedingungen durch nate, le dimethoxyethane et le chlorure de methy- Mittel erreicht werden, die aus der Zugabe einer 10 lene. wirksamen Menge eines Amins oder Sattigung der Reaktionslosung mit wasserfreiem Ammoniak aus- 3. Le procede de la revendication 1 , caracterise en ce gewahlt werden. que le sel de lithium reactant est selectionne parmi le chlorure de lithium, le bromure de lithium, le per- 6. Verfahren nach Anspruch 1, iiberdies gekenn- is chlorate de lithium, le nitrate de lithium, I'acetate de zeichnet durch Riickgewinnung des Lithiumhe- lithium, le tetrafluoroborate de lithium ou le ben- xafluorophosphats aus der Losung durch Filtern zoate de lithium. der Ausgangsproduktlosung, Zugabe eines hoher- siedenden Losungsmittels, das aus Ethylencarbo- 4. Le procede de la revendication 1 , caracterise en ce nat oder Propylencarbonat ausgewahlt wird, zu der 20 que le sel organohexafluorophosphate reactant est anfanglichen Produktlosung aus Lithiumhexafluo- un hexafluorophosphate d'ammonium tetraalkyle rophosphat und Entfernen des anfanglichen nied- ayant la formule R4NPF6, dans laquelle R est selec- rigsiedenden Losungsmittels und Ammoniaks oder tionne parmi des groupes alkyles de 1 a 8 atomes Amins durch Erhitzen unter Vakuum. de carbone. 25 7. Verfahren zur Herstellung von Losungen aus Lithi- 5. Le procede de la revendication 1 , caracterise en ce umhexafluorophosphat, gekennzeichnet durch das que les conditions basiques sont obtenues par des zur Reaktion bringen, unter basischen Bedingun- moyens selectionnes parmi I'ajout d'une quantite gen, von Kaliumhexafluorophosphatsalz mit Lithi- efficace d'une amine ou la saturation de la solution umchlorid in Acetonitril zur Herstellung einer 30 de reaction avec un ammoniac anhydre. Losung aus Lithiumhexafluorophosphat und prazi- pitiertem Kaliumchlorid, wahrend die Losung durch 6. Le procede de la revendication 1, caracterise de Sattigung der Losung mit wasserfreiem Ammoniak plus par la recuperation de I'hexafluorophosphate basisch gehalten wird. de lithium a partir de la solution en f iltrant la solution 35 de produit originale, I'ajout d'un solvant a point 8. Verfahren nach Anspruch 7, iiberdies gekenn- d'ebullition plus eleve, selectionne parmi le carbo- zeichnet durch Riickgewinnung des Lithiumhe- nate d'ethylene ou le carbonate de propylene, a la xafluorophosphats aus der Losung durch Filtern solution de produit initiale d'hexafluorophosphate der Ausgangsproduktlosung, Zugabe eines hoher- de lithium et I'extraction du solvant initial a faible siedenden Losungsmittels, das aus Ethylencarbo- 40 point d'ebullition et de I'ammoniac ou de I'amine en nat oder Propylencarbonat ausgewahlt wird, zu der chauffant sous vide. anfanglichen Produktlosung aus Lithiumhexafluo- rophosphat und Entfernen des anfanglichen nied- 7. Un procede pour la preparation de solutions rigsiedenden Losungsmittels und Ammoniaks oder d'hexafluorophosphate de lithium, caracterise par Amins durch Erhitzen unter Vakuum. 45 la reaction, dans des conditions basiques, de sel de hexafluorophosphate de potassium avec du chlo- Revendications rure de lithium dans I'acetonitrile pour produire une solution d'hexafluorophosphate de lithium et un 1. Un procede pour la preparation de solutions precipite de chlorure de potassium tout en mainte- d'hexafluorophosphate de lithium, caracterise par so nant la solution basique en saturant la solution avec la reaction, dans des conditions basiques, d'un sel de I'ammoniac anhydre. de lithium avec un sel selectionne parmi les hexa- fluorophosphates de sodium, de potassium, 8. Le procede de la revendication 7, caracterise de d'ammonium ou d'ammonium tetraalkyle dans un plus par la recuperation de I'hexafluorophosphate solvant organique non pratique a bas point d'ebulli- 55 de lithium a partir de la solution en f iltrant la solution tion, dans une zone de reaction qui est continuelle- de produit originale, I'ajout d'un solvant a point ment saturee avec un compose selectionne parmi d'ebullition plus eleve, selectionne parmi le carbo- I'ammoniac anhydre, le methylamine ou I'ethyla- nate d'ethylene ou le carbonate de propylene, a la

5 9 EP 0 735 983 B1 10 solution de produit initiale d'hexafluorophosphate de lithium et I'extraction du solvant initial a faible point d'ebullition et I'ammoniac ou I'amine en chauffant sous vide. 5