Method of Purifying Lithium Hexafluorophosphate Verfahren Zur Reinigung Von Lithiumhexafluorphosphat Procede Permettant De Purifier L’Hexafluorophosphate De Lithium

Europäisches Patentamt *EP001055640B1* (19) European Patent Office

Office européen des brevets (11) EP 1 055 640 B1

(12) EUROPEAN PATENT SPECIFICATION

(45) Date of publication and mention (51) Int Cl.7: C01B 25/445, C01D 15/00 of the grant of the patent: 30.06.2004 Bulletin 2004/27 (86) International application number: PCT/JP1999/006386 (21) Application number: 99972189.7 (87) International publication number: (22) Date of filing: 16.11.1999 WO 2000/029324 (25.05.2000 Gazette 2000/21)

(54) METHOD OF PURIFYING LITHIUM HEXAFLUOROPHOSPHATE VERFAHREN ZUR REINIGUNG VON LITHIUMHEXAFLUORPHOSPHAT PROCEDE PERMETTANT DE PURIFIER L’HEXAFLUOROPHOSPHATE DE LITHIUM

(84) Designated Contracting States: • FUKUDOME, Toshirou DE FR GB IT Stella Chemifa Kabushiki Kaisha Sakai-shi, Osaka 590-0982 (JP) (30) Priority: 17.11.1998 JP 32731998 • WAKI, Masahide Stella Chemifa Kabushiki Kaisha (43) Date of publication of application: Sakai-shi, Osaka 590-0982 (JP) 29.11.2000 Bulletin 2000/48 (74) Representative: Dr. Weitzel & Partner (73) Proprietors: Friedenstrasse 10 • Stella Chemifa Kabushiki Kaisha 89522 Heidenheim (DE) Osaka-shi, Osaka-fu 541-0047 (JP) • Yazaki, Hiroshi (56) References cited: Sakai-shi, Osaka 590-0982 (JP) WO-A-99/40027 JP-A- 6 298 506 JP-A- 10 072 207 JP-A- 10 092 468 (72) Inventors: JP-A- 11 147 705 JP-A- 59 081 870 • YAZAKI, Hiroshi Stella Chemifa Kabushiki Kaisha • PATENT ABSTRACTS OF JAPAN vol. 1995, no. Sakai-shi, Osaka 590-0982 (JP) 01, 28 February 1995 (1995-02-28) & JP 06 298507 • KIKUYAMA, Hirohisa A (CENTRAL GLASS CO LTD), 25 October 1994 Stella Chemifa Kabushiki Kaisha (1994-10-25) Sakai-shi, Osaka 590-0982 (JP)

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 a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention). EP 1 055 640 B1

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Description or phosphorus pentafluoride to be used are required to be refined to a high purity, increasing cost and affecting Technical Field of Invention considerably the product price. [0008] Therefore, none of conventional method was [0001] The present invention concerns a method of 5 satisfactory. purifying lithium hexafluorosphate that allows to purify [0009] It is an object of the present invention to pro- lithium hexafluorophosphate, useful as, for instance, vide a method of purifying lithium hexafluorosphate that lithium secondary cell electrolyte, organic synthesis me- allows to obtain high purity lithium hexafluorophos- dium or the like, to an extremely high purity. phate, by converting hydrogen fluoride, oxyfluoride, lith- 10 ium fluoride or other impurities, generated in the course Prior Art of production, handling or conservation of lithium hexafluorophosphate and mixed with the product, into lithi- [0002] Lithium hexafluorophosphate is usually syn- um hexafluorophosphate. thesized in an insoluble medium such as hydrofluoric anhydride or organic medium; however it reacts with a 15 Disclosure of the Invention trace of water existing in the medium, and generates oxyfluoride and lithium fluoride etc., then they are mixed [0010] The method of purifying lithium hexafluor- into the product and contaminates the same. osphate of the present invention is characterized by that [0003] Besides, lithium hexafluorophosphate decom- the purification is performed by introducing phosphorus poses and equilibrates partially as shown in the follow- 20 pentachloride and hydrogen fluoride of the quantity nec- ing expression, when it is dissolved in hydrofluoric an- essary for producing phosphorus pentafluoride of the hydride or organic medium. quantity more than necessary for converting rude lithium hexafluorophosphate and oxyfluoride in the raw materi- al into lithium hexafluorophosphate, in the reaction sys- LiPF ←→LiF + PF 6 5 25 tem with brut lithium hexafluorophosphate and reacting them. [0004] This LiF is mixed into the product and becomes impurity. Effect [0005] As lithium hexafluorophosphate has an extremely high moisture absorption ability, even a trace of 30 [0011] In the present invention, impurities such as hy- humidity in the atmosphere provokes hydrolysis to gen- drogen fluoride, oxyfluoride, lithium fluoride contained erate hydrofluoric acid portion. In addition, lithium fluo- in lithium hexafluorophosphate are converted into lithi- ride or lithium oxyfluorophosphate (LiPOxFy) is gener- um hexafluorophosphate by adding phosphorus pen- ated to cause impurity. If lithium hexafluorophosphate tachloride for the purification. At this moment, phospho- containing such impurities is used as lithium cell elec- 35 rus pentachloride and hydrogen fluoride of equal or su- trolyte, hydrofluoric acid erodes into the electrode ma- perior to the equivalent amount are introduced for react- terial, and lithium fluoride becomes residue as it is in- ing them. soluble to organic medium and requires filtration and re- [0012] At this moment, phosphorus pentachloride re- moval, while lithium oxyfluorophosphate accelerates acts with hydrogen fluoride to generate phosphorus the decomposition of organic medium, and possibly in- 40 pentafluoride: creases inner voltage, lowers cell capacity, or inflames. [0006] Conventionally, these impurities can be re- PCl + 5HF → PF + 5HCl (1) moved, by a method wherein lithium hexafluorophos- 5 5 phate is dissolved in an organic medium and impurities are removed by an ion exchange {exchange} resin (Jap- 45 The generated phosphorus pentafluoride reacts respec- anese Patent Laid-Open No. SHOU 59-87774) or a tively with oxyfluoride and lithium fluoride as follows to method for neutralizing in an organic medium (Japa- be converted into lithium hexafluorophosphate and pu- nese Patent Laid-Open No. SHOU 59-81870); however, rified. these methods dissolve once into an organic medium, increasing the production process and costs. 50 [0007] Moreover, a method for reacting and removing LiPOxFy + PF5 → LiPF6 + POzFy-1 (2) oxyfluorophosphate with fluorine gas (Japanese Patent Publication No. HEI 4-16406, Japanese Patent Publica- tion No. HEI 4-16407) or a method for making hexafluor- LiF + PF5→ LiPF6 (3) ophosphate contact with a gas containing pentafluoro- 55 phosphate (Japanese Patent Laid-Open No. HEI [0013] The reaction shown by the formula (1) devel- 6-298507) or the like involve danger in gas treatment ops quantitatively at the room temperature and normal and require special knowledge. Moreover fluorine gas

2 3 EP 1 055 640 B1 4 pressures. By-product hydrochloric gas is not involved Best Embodiments of the Invention into the reaction and discharged from the system with- out depositing to the product or remaining, because of (Embodiment 1) high vapor pressure. [0014] The ratio of phosphorus pentachloride to hy- 5 [0018] 500 g of brut lithium hexafluorophosphate con- drogen fluoride is desirable that hydrogen fluoride be taining 4% of hydrogen fluoride, 50ppm of oxyfluoride equal or superior to chemical equivalent amount; how- (LiPOF4) and 0.13% of lithium fluoride is taken in a PFA ever, even if phosphorus pentachloride is in excess and vessel of 1L, 5.5g of phosphorus pentachloride is added remains non-reacted, it can be removed by heating at thereto and mixed well, then the vessel is sealed with an temperature equal or superior to 100°C because its 10 nitrogen gas flow, heated a whole night at 101 kPa sublimation temperature is 100°C (760Torr), 105°C for reaction. Remaining gas is purged [0015] The reaction of phosphorus pentafluoride and by nitrogen gas to obtain purified lithium hexafluoro- oxyfluoride shown in the formula (2) and the reaction of phosphate. Impurities thereof are quantified to deter- phosphorus pentafluoride and lithium fluoride shown in mine hydrogen fluoride 30ppm, oxyfluoride 10ppm or the formula (3) depend on the temperature. The reaction 15 less and lithium fluoride 0.04%. Note that the stoichio- develops easily if the temperature is high. However, as metric amount of phosphorus pentachloride required for the temperature attains 250°C or more, the counter-re- oxyfluoride and lithium fluoride being 5.3g, it is added action as shown below will occur, increasing the content here by 1.0 time. of lithium fluoride as impurity. Fig. 1 shows an example of differential thermal analysis of lithium hexafluoro- 20 (Comparative Example 1) phosphate. [0019] 500 g of brut lithium hexafluorophosphate containing 4% of hydrogen fluoride, 50ppm of oxyfluoride LiF + PF5 ←→LiPF6 (LiPOF4) and 0.13% of lithium fluoride is taken in a PFA 25 vessel of 1L, 2.7g of phosphorus pentachloride, about >250°C (4) half of required amount for converting impurities into lithium hexafluorophosphate is added thereto and mixed [0016] Though the reaction of phosphorus pentafluo- well, then it is operated as in (Embodiment 1) thereafter. ride with oxyfluoride, lithium fluoride proceeds sufficient- Impurities in the obtained product thereof are quantified ly around the normal pressure, it is desirable that the 30 to determine hydrogen fluoride 50ppm, oxyfluoride reaction develops under the pressure. If the reaction 30ppm and lithium fluoride 0.08%, showing that impuri- system is put under negative pressure, not only the re- ties have been converted into lithium hexafluorophos- action of phosphorus pentafluoride with oxyfluoride, lith- phate rather insufficiently. Note that phosphorus pen- ium fluoride proceeds hardly, but, on the contrary, lithi- tachloride was added by half of the stoichiometric um hexafluorophosphate decomposed increasing im- 35 amount of the Embodiment 1. purities. This is shown, in Fig. 2, by the relationship between free acid and insoluble residue by the inner pres- (Embodiment 2) sure of the reaction system. Additionally, the time necessary for this generation reaction depends on condi- [0020] 500 g of brut lithium hexafluorophosphate con- tions such as temperature or pressure, and the content 40 taining 150ppm of hydrogen fluoride and 0.5g of lithium of hydrogen fluoride, oxyfluoride and lithium fluoride in fluoride is taken in a PFA vessel of 1L, 4.0g of phospho- lithium hexafluorophosphate used for the generation, rus pentachloride is added thereto and mixed well. Fur- however several hours to a whole day and night are suf- ther, 2.0g of liquid hydrogen fluoride corresponding to ficient. When the purification reaction is completed, phosphorus pentachloride is added. The vessel is through dry nitrogen gas, remaining hydrogen fluoride, 45 sealed with nitrogen gas flow, heated a whole night at phosphorus pentafluoride, hydrogenchloride, and non- 101 kPa (760Torr), 105°C for reaction. Remaining gas reacted phophorus pentachloride gas are purged com- is purged by nitrogen gas to obtain purified lithium hex- pletely. afluorophosphate, Impurities thereof are quantified to determine hydrogen fluoride 40ppm and lithium fluoride Brief Description of Drawings 50 0. 02%. Note that the stoichiometric amount of hydrogen fluoride for 4.0g of phosphorus pentachloride is 1.9g. [0017] (Comparative Example 2) Fig. 1 is a graph showing the results of differential thermal analysis of lithium hexafluorophosphate. 55 [0021] 500 g of brut lithium hexafluorophosphate con- Fig. 2 is a graph showing the relationship between taining 150ppm of hydrogen fluoride and 0.10% of lithi- inner pressure of the reaction system, free acid and um fluoride is taken in a PFA vessel of 1L, 4.0g of phos- insoluble residue. phorus pentachloride is added thereto and mixed well.

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Further, phosphorus pentachloride and 0.9g of liquid hy- lithium fluoride 0.01%. Note that stoichiometric amount drogen fluoride, about half of the equivalent amount, are of phosphorus pentachloride of the Embodiment 3 is added thereto, and then it is operated as in (Embodi- added. ment 2) thereafter. Impurities in the obtained product thereor are quantified to determine hydrogen fluoride 5 (Example 4) 20ppm and lithium fluoride 0.05%, showing that lithium fluoride was converted into lithium hexafluorophosphate [0025] 1kg of brut lithium hexafluorophosphate con- insufficiently. Note that hydrogen fluoride was added by taining 0.5% of hydrogen fluoride and 0.11% of lithium half of the stoichiometric amount of the Embodiment 2. fluoride is taken in a 3L vessel made of SUS316, 9.0g 10 of phosphorus pentachloride is added thereto and (Embodiment 3) mixed well. It is heated to 105°C and made react for 10 hours. At this moment, the vessel inner pressure has [0022] 1kg of brut lithium hexafluorophosphate con- been lowered to 53kPa (400Torr) by a vacuum pump. taining 0.5% of hydrogen fluoride and 0.11% of lithium After completion of the reaction, nitrogen gas is blown fluoride is taken in a 3L vessel made of SUS316, 9.0g 15 inside. Impurities in the obtained lithium hexafluoro- of phosphorus pentachloride is added thereto and phosphate are analyzed to determine hydrogen fluoride mixed well. It is placed in a humidifier maintained at 20ppm and lithium fluoride 0.26%. Lithium hexafluoro- 200°C and made react for 6 hours. At this moment, as phosphate has decomposed by decompression and the vessel inner pressure has increased, it is adjusted heating. Note that stoichiometric amount of phosphorus to more or less 200kPa (1500Torr). After completion of 20 pentachloride of the Embodiment 3 is added. the reaction, the inner pressure is vented, and further gas remained inside is purged by nitrogen gas to obtain Industrial Domain of Application purified lithium hexafluorophosphate-Impurities thereof are analyzed to determine hydrogen fluoride 25ppm and [0026] The present invention allows to purify easily lithium fluoride 0.02%. Note that, in this embodiment, 25 lithium hexafluorophosphate, useful as lithium second- chemical equivalent amount of phosphorus pentachlo- ary cell electrolyte or organic synthesis medium. It is ride necessary for lithium fluoride is added. characterized by that harmful impurities such as oxyfluoride and lithium fluoride or the like are made to react (Example 3) in the presence of phosphorus pentachloride and hy- 30 drofluoric acid euql or superior to the equivalent amount, [0023] 1kg of brut lithium hexafluorophosphate con- and oxyfluoride and lithium fluoride are converted into taining 0.5% of hydrogen fluoride and 0.11% of lithium lithium hexafluorophosphate by means of phosphorus fluoride is taken in a 3L vessel made of SUS316, 9.0g. pentafluoride to be purified. The use of phosphorus pen- of phosphorus pentachloride is added thereto and tachloride is cheap in cost, and the handling is easy as mixed well. It is placed in a humidifier maintained at 270 35 phosphorus pentachloride is solid. On the contrary, a to 280°C and made to react for 6 hours. At this moment, method to refine lithium hexafluorophosphate to a high as the vessel inner pressure has increased, it is adjusted purity with gas containing phosphorus pentafluoride in- to more or less 200 kPa (1500 Torr). Thereafter, it is op- volves danger as gas is handled directly, and requires erated as in (Embodiment 3). Impurities in the obtained specialized knowledge. Moreover, the production of lithium hexafluorophosphate are analyzed to determine 40 high purity phosphorus pentafluoride required for the hydrogen fluoride 20ppm and lithium fluoride 0.2%. Lith- purification costs extremely high. ium hexafluorophosphate has decomposed as the tem- [0027] According to the present invention, a great ef- perature was too high. Note that phosphorus pentachlo- fect can be expected for producing cheaply and in quan- ride is added as much as Embodiment 3. tity high purity lithium hexafluorophosphate by using 45 phosphorus pentachloride in the course of purification. (Embodiment 4)

[0024] 1kg of brut lithium hexafluorophosphate con- Claims taining 0.5% of hydrogen fluoride and 0.11% of lithium fluoride is taken in a 3L vessel made of SUS316, 9.0g 50 1. A method for purifying lithium hexafluorophosphate of phosphorus pentachloride is added thereto and (LiPF6) from the impurities lithium oxyfluorophos- mixed well. It is heated to 105°C and made react for 10 phate (LiPOxFy) and/or lithium fluoride (LiF) and/or hours. At this moment, the vessel inner pressure has hydrogen fluoride (HF), wherein attained 333kPa (2500Torr). After completion of the reaction, the inner pressure is vented, and further gas re- 55 1.1 the reaction pressure is equal or superior mained inside is purged by nitrogen gas to obtain puri- to 9.04 104 Pa (680 Torr): fied lithium hexafluorophosphate. Impurities thereof are 1.2 Phosphorus pentachloride (PCl5) is added analyzed to determine hydrogen fluoride 20ppm and at least in a sufficient amount to react with the

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total amount of hydrogen fluoride (HF) present Revendications and, if necessary, such an additional amount of hydrogen fluoride (HF) is added to generate an 1. Procédé pour purifier l'hexafluorophosphate de li- excess quantity of phosphorus pentafluoride thium (LiPF6) des impuretés oxyfluorophosphate de 5 (PF5) for the reaction with the total amount of lithium (LiPOxFy) et/ou fluorure de lithium (LiF) et/ the impurities lithium oxyfluorophosphate ou fluorure d'hydrogène (HF) dans lequel : (LiPOxFy) and lithium fluoride (LiF). - la pression de réaction est égale ou supérieure 2. The method of purifying lithium hexafluorophos- à 9,04 x 104 Pa (680 Torr); 10 phate of claim 1, wherein the hydrogen fluoride - du pentachlorure de phosphore (PCl5) est ajou- used for the reaction is liquid and/or gas. té au moins en quantité suffisante pour réagir avec la quantité totale de fluorure d'hydrogène 3. The method of purifying lithium hexafluorosphate of (HF) présente et si nécessaire, il est ajouté la claim 1 or 2, wherein the reaction temperature is quantité supplémentaire de fluorure d'hydrogè- within the range from the room temperature to 15 ne (HF) requise pour créer un excédent de pen- 250°C or below. tafluorure de phosphore (PF5) pour réagir avec la quantité totale des impuretés oxyfluorophos- 4. The method of purifying lithium hexafluorosphate of phate de lithium (LiPOxFy) et fluorure de lithium claim 1 to 3, wherein the reaction pressure is 1.01 (LiF). 105 Pa to 5,05 105 Pa (760 to 3800 Torr). 20 2. Procédé de purification de l'hexafluorophosphate de lithium de la revendication 1, dans lequel le fluo- Patentansprüche rure d'hydrogène utilisé pour la réaction est liquide et/ou gazeux. 1. Verfahren zur Reinigung von Lithiumhexafluoro- 25 phosphat (LiPF6) von den Verunreinigung Lithi- 3. Procédé de purification de l'hexafluorophosphate umoxyfluorophosphat (LiPOxFy) und/oder Lithium- de lithium de la revendication 1 ou 2, dans lequel la fluorid (LIF) und/oder Fluorwasserstoff (HF), worin température de réaction est comprise entre la tem- pérature ambiante et 250°C ou moins. 1.1 der Reaktionsdruck gleich oder größer als 30 9,04 104 Pa (680 Torr) ist; 4. Procédé de purification de l'hexafluorophosphate 1.2 Phosphorpentachlorid (PCl5) wenigstens in de lithium de l'une des revendications 1 à 3, dans einer ausreichenden Menge zugesetzt wird, lequel la pression de réaction est de 1,01 x 105 Pa um mit der Gesamtmenge an vorhandenem à 5,05 x 105 Pa (760 à 3800 Torr). Fluorwasserstoff (HF) zu reagieren, und erfor- 35 derlichenfalls eine solche zusätzliche Menge an Fluorwasserstoff (HF) zugesetzt wird, daß eine Überschußmenge an Phosphorpentafluo- rid (PF5) für die Reaktion mit der Gesamtmen- ge der Verunreinigungen Lithiumoxyfluoro- 40 phosphat (LiPOxFy) und Lithiumfluorid (LiF) er- zeugt wird.

2. Verfahren zur Reinigung von Lithiumhexafluoro- phosphat nach Anspruch 1, worin der zur Reaktion 45 verwendete Fluorwasserstoff flüssig und/oder gas- förmig ist.

3. Verfahren zur Reinigung von Lithiumhexafluoro- phosphat nach Anspruch 1 oder 2, worin die Reak- 50 tionstemperatur im Bereich zwischen Raumtempe- ratur und 250°C oder darunter liegt.

4. Verfahren zur Reinigung von Lithiumhexafluoro- phosphat nach Anspruch 1 bis 3, worin der Reakti- 55 onsdruck 1,01 105 Pa bis 5,05 105 Pa (760 bis 3800 Torr) beträgt.

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