FR2852945A1 - Solid-state synthesis of lithium hexafluorophosphate, useful as a battery electrolyte, comprises reacting a lithium source with diammonium phosphate and reacting the product with ammonium fluoride - Google Patents

Abstract

Solid-state synthesis of lithium hexafluorophosphate comprises mixing a lithium source (oxide or salt) with diammonium phosphate, heating the mixture at 150-600 [deg]C, cooling and pulverizing the product, mixing the product with a 6- to 9-fold amount of ammonium fluoride, heating the mixture at 150-400 [deg]C for 4-6 hours in a sealed PTFE vessel, and transferring the product to a dry receptacle.

Description

Ca ne Beud oménie

  The present invention relates to a process for the preparation of lithium hexafluorophosphate (LiPF6). More particularly, the present invention relates to a process for the preparation of lithium hexafluorophosphate (LiPF6) useful as battery electrolyte, in particular for batteries of the “rocking chair” or “steering wheel” type (that is to say in which lithium ions describe a back and forth movement between the anode and the cathode) and other nonaqueous lithium batteries and lithium electrolyte in the form of solid polymer.

  LiPF6 is a well known electrolyte for secondary lithium batteries which is difficult to prepare due to the high activity of raw materials such as P205, Li2O and PF5 and F2. However, there are a small number of chemical processes available in the literature, but they require careful purification and handling. In addition, these methods require a wide range of equipment to process and prepare this essential chemical for "rocking chair" or lithium ion or intercalation type battery systems.

  Phosphorus metal fluorides such as MPF6 or M is 20 Ca, K or Li can be prepared by reaction of MF with PF3 (Paul et al., Fluorine Chemistry, 56, 1995) according to the reaction: 3MF + 5PF3 - * 3MPF6 + 2P o M is Ca, K or Li. MPF6 can be prepared by neutralizing HPF6 with an appropriate base, namely, 2HPF6 + Ca (OH) 2 - Ca (PF6) 2 + 2 H2O Similarly, some of the hexafluorophosphates by double decomposition of NH4PF6 or KPF6 (Paul et al., Fluorine Chemistry, 56, 1995; Fluorine Chemistry, vol. 5, Simons JH, 131 (1819), 1964; Fluorine Chemistry, vol. 1, Emelson HJ, 76 ( 219), 1995). LiPF6 30 prepared by previous processes has certain disadvantages, for example toxic chemicals are required as reactants, it becomes difficult to handle the chemicals involved, the final product contains unreacted impurities, the reaction is not only partial, additional steps are required for preparation and it is not a pure solid reaction.

  Cabinet Beau de Loménie The main object of the present invention is to provide a process for the synthesis of lithium hexafluorophosphate (LiPF6) as a battery electrolyte.

  Another object of the present invention is to provide a complete solid state reaction.

  Yet another object of the present invention is to avoid the many active chemicals which are difficult to handle.

  Yet another object of the invention is to avoid toxic gases.

  Yet another object of the invention is to obtain a product in the absence of partial reaction.

  These and other objects of the invention are achieved and the problems associated with the state of the art resolved by the method of the invention described below.

  A process for the preparation of LiPF6 (lithium hexafluorophosphate) is developed o equimolar amounts of a source of dry pure lithium such as reactive quality that Li2O or Li2CO3 or LINO3 are mixed with very pure dry samples of reactive quality d Dammonium hydrogen phosphate and the mixture is heated continuously for 6 h between 2000 and 6000C in an electric oven.

  The product is cooled and then transferred to a dry container.

  The product is a transparent substance whose X-ray analysis confirms that it is LiPF6.

  Therefore, the present invention provides a solid state thermal process for the synthesis of lithium hexafluorophosphate (LiPF6) which comprises the steps of: (a) mixing a lithium source selected from the group consisting of an oxide lithium, a lithium salt or a combination thereof with diammonium phosphate; (b) heating the mixture in an oven at a temperature of the order of 1500C to 6500C continuously to obtain LiPO3; (c) cooling and spraying LiPO3; (d) mixing the sprayed product with six to nine times its amount of ammonium fluoride, then heating it to a temperature of the order of 1500C to 4000C using a continuous oven for 4 to 6 h in a closed container Teflon; (e) transfer the product to a dry container.

  In one embodiment of the invention, step (b) above is implemented for a period of the order of 4 to 6 h. In one embodiment of the present invention, LiPO3 is mixed with NH4F in the ratio 1: 6 to 9 to form LiPF6.

  In another embodiment of the invention, lithium metaphosphate (LiPO3) is mixed with ammonium fluoride in the ratio of 1: 7 and the mixture is heated to 200 ° C. in an electric oven for 6 hours continuously to obtain lithium hexafluorophosphate 10.

  In yet another embodiment of the invention, Li2CO3 or Li20 or LiNO3 is mixed with diammonium hydrogen phosphate and ammonium fluoride in molar ratios of 1: 2: 6 to 9.

  In another embodiment of the invention, Li2CO3 or Li20 or LiNO03 is mixed with diammonium hydrogen phosphate and ammonium fluoride in the ratio of 1: 1: 7.

  In yet another embodiment of the invention, Li20 or LiNO03 is mixed with diammonium hydrogen phosphate and ammonium fluoride in the ratio of 1: 1: 7 and the mixture is heated to 200 C continuously for 12 h in an electric oven to obtain LiPF6.

  In one embodiment of the invention, Li2CO3 or Li20 or LiNOO3 is mixed with diammonium phosphate in the ratio 1: 1, then the product is mixed with NH4F in the ratio of 1: 7 and heated.

  In yet another embodiment of the invention, the temperature is maintained between 150 and 350 C for the preparation of LiPF6 when LiN03 or Li20 is the starting product.

  In another embodiment of the invention, in the case of Li2CO3, the heating temperature with (NH4) 2HP04 is around 600 C, and then mixed with NH4F and heated, the temperature being maintained between 150 and 350 C.

  In another embodiment of the invention, the reactions are carried out in the solid state.

  In yet another embodiment of the invention, the method comprises a two-step reaction as follows (a) 3000C 2 (NH4) 2HPO4 + Li2O - 2 LiPO3 + 4NH3 + 3H20 6000C 2 (NH4) 2HP04 + Li2CO3 - -> 2 LiPO3 + 4NH3 + C02 + 3H20 300 C 2 (NH4) 2HP04 + 2 LiNO3 -> 2 LiPO3 + 4NH3 + 2N02 + 2H20 + 02> 150-300 C (b) LiPO3 + 6NH4F -> LiPF6 + 6NH3 + 3:20 In yet another embodiment of the invention, it is possible to use a single step process at a temperature of 150-3000C.

  Li2O + 2 (NH4) 2HP04 + 12 NH4F -> 2 LiPF6 + 16NH3 + 9H20 Li2CO3 + 2 (NH4) 2HP04 + 12 NH4F -> 2 LiPF6 + 16NH3 + C02 + 9H20 LiNO3 + 2 (NH4) 2HP04 + 12 NH4F -> 2 LiPF6 + 16NH3 + NO2 + 9H20 In another embodiment of the invention, pure dry Li20 or Li2CO3 or LiNO3 is mixed with twice the amount of diammonium phosphate, that is to say in the molar ratio of 1: 2 and the mixture is heated in an electric or muffle furnace for 6 h at a temperature of 600 C continuously in the case of Li2CO3 and approximately 25 300 C in the case of Li20 and LiNO3. The product is dried at 80 ° C., then allowed to react with NH4F in the molar ratio of 1:> 6-8 for 4 h in a continuous electric oven at a temperature of the order of 150 to 3500C.

  In yet another embodiment of the invention, all of the materials are in the solid state.

  A feature of the invention is that an electric oven can be used for the process.

  Another feature of the invention is that a muffle furnace can be used for the process.

  In yet another embodiment of the invention, it is possible to use a single-step process, namely> 150-3000C (a) LiPO3 + 6NH4F -> LiPF6 + 6NH3 + 3H20 Lithium hexafluorophosphate is an essential chemical for "rocking chair" or "steering wheel" batteries, the 5 lithium ion batteries and intercalation battery systems.

  However, the preparation of this compound by the prior methods is difficult and has many drawbacks.

  The invention relates to a solid state thermal process for preparing LiPF6 which overcomes the above difficulties. It comprises a solid state reaction of a lithium salt or a lithium oxide or a combination of these with diammonium phosphate in equimolar proportions, which makes it possible to obtain a mixture of the two compounds. The mixture is then heated in an oven at 6000C and the product obtained is sprayed after cooling. It is then mixed with ammonium fluoride at six times the amount of LiPO3 obtained from the reaction, then heated to 2000C using a continuous oven for 4 to 6 h in a closed Teflon container.

  The main advantages of the invention are first of all the absence of secondary reaction, secondly the possibility of a one-step or two-step process depending on the method of approach, thirdly the obtaining of a pure sample of LiPF6, fourthly the possibility of a purely solid reaction under thermal control, since no gas or liquid is used, even for the initial reaction, fifthly the purity of the product which depends on the purity of the reagents and finally the simplicity, the non-complexity and the excellent yield of the process.

  The invention will now be described in detail with reference to the following examples which are purely illustrative and therefore are not intended to limit the scope of the invention in any way.

Example 1

  An equimolar mixture of Li2CO3 (reactive quality) and (NH4) 2HP04 (reactive quality) is ground, mixed and heated at 6000C 35 in an electric / muffle oven for 6 h continuously, then the product is ground and mixing with NH4F (reactive quality) and the mixture is again heated in an electric oven / muffle oven for 4 h at a temperature of 200 C.

  Components Composition First stage Li2CO3 0.74 g (NH4) 2HPO4 1.32 g Granulometry of the mixture 5 pm Temperature 600 C Duration 6 h Second stage NH4F 2.6 g Temperature 600 C Duration 4 h Appearance of the product Transparent Process yield> 90 %

Example 2

  An equimolar mixture of Li20 (reactive quality) and (NH4) 2HPO4 (reactive quality) is ground, mixed and heated at 600 ° C. in an electric / muffle furnace for 6 h continuously, then the product is ground and mixed with NH4F (reactive quality) and the mixture is again heated in the electric oven / muffle oven for 4 h at a temperature of 200 C.

  Components Composition First stage Li20 0.3 g (NH4) 2HPO4 1.32 g Granulometry of the mixture 5 pm Temperature 400 C Duration 6 h Second stage NH4F 2.6 g Temperature 200 C Duration 4 h Appearance of the product Transparent Process yield> 90 %

Example 3

  An equimolar mixture of LiNO3 (reactive quality) and (NH4) 2HPO4 (reactive quality) is ground, and mixed and heated at 4000C in an electric / muffle oven for 6 h continuously, then the product is ground and mixing with NH4F (reactive quality) and the mixture is again heated in the electric oven / muffle oven for 4 h at a temperature of 200 C.

  Components Composition First stage LiNO3 0.69 g (NH4) 2HP04 1.32 g Granulometry of the mixture 5 pm Temperature 400 C Duration 6 h Second stage NH4F 2.6 g Temperature 200 C Duration 4 h Appearance of the product Transparent Process yield> 90 %

Example 4

  Take an equimolar mixture of lithium metaphosphate (LiPO3) and ammonium fluoride in the ratio 1:> 6 to 8, mix and grind, then heat in an electric oven / muffle oven, continuously for 4 h at 200 C until the final product is formed.

  Components Composition First stage LiNO3 0.69 g (NH4) 2HP04 1.32 g Granulometry of the mixture 5 pm Temperature 600 C Duration 6 h Second stage NH4F 2.6 g Temperature 600 C Duration 4 h Appearance of the product Transparent Process yield> 90 %

Example 5

  A mixture of Li2O, (NH4) 2HPO4 (reactive quality) and NH4F is taken in the ratio of 1: 2: 7 and it is heated in an electric / muffle furnace for 6 h at a temperature of 300 C, continuously.

  Components Composition Li2O 0.30 g (NH4) 2HPO4 1.32 g NH4F 2.60 g Granulometry of the mixture 5 pm Temperature 300 C Duration 6 h Nature of the product Transparent Process yield> 90%

Example 6

  A mixture of Li2CO3, (NH4) 2HPO4 (reactive quality) and NH4F is taken in the ratio of 1: 2: 7 and it is heated in an electric / muffle furnace for 6 h at a temperature of 3000C continuously.

  Components Composition Li2CO3 0.74 g (NH4) 2HPO4 1.32 g NH4F 2.60 g Granulometry of the mixture 5 pIm Duration 6 h Temperature 300 C Appearance of the product Transparent Process yield> 90%

Example 7

  A mixture of LiNO3, (NH4) 2HPO4 (reactive quality) and NH4F is taken in the ratio of 1: 2: 7 and it is heated in an electric / muffle oven for 4 h at a temperature of 300 C continuously.

  Components LiNO3 (NH4) 2HPO4 NH4F Granulometry of the mixture Duration Temperature Appearance of the product Process yield Composition 0.69 g 1.32 g 2.60 g 5 Pm 4h 300 C Transparent> 90% (_Cabinet Beau de Loménie

Claims (18)

  1. A solid state thermal process for the synthesis of lithium hexafluorophosphate (LiPF6), characterized in that it comprises the steps consisting in: (a) mixing a lithium source chosen from the group consisting of a oxide of lithium, a lithium salt or a combination thereof with diammonium phosphate; (b) heating the mixture in an oven at a temperature of the order of 150 ° C. to 600 ° C. continuously to obtain the product LiPO3; (c) cooling and spraying the LiPO3 product; (d) mix the sprayed product with six to nine times its quantity of ammonium fluoride, then heat it to a temperature of the order of 150 ° C. to 400 ° C. using a continuous oven for 4 to 6 h 15 min in a closed Teflon container; (e) transfer the product to a dry container.   2. Method according to claim 1 characterized in that LiPO3 is mixed with NH4F in the ratio of 1: 7 to form LiPF6.   3. Method according to any one of claims i and 2 20 characterized in that step (b) is implemented for a period of the order of 4 to 6 h. 4. Method according to any one of the preceding claims, characterized in that the lithium metaphosphate (LiPO3) is mixed with the ammonium fluoride in the ratio of 1: 7 and the mixture is heated to 200 C in an electric oven for 6 hours continuously to obtain lithium hexafluorophosphate.   5. Method according to any one of the preceding claims, characterized in that Li2CO3 or Li2O or LiNO3 is mixed with diammonium hydrogen phosphate and ammonium fluoride in the molar ratio of 1: 2: 6 to 9.   6. Method according to any one of claims i to 4 characterized in that Li2CO3 or Li20 or LiNO3 is mixed with diammonium hydrogen phosphate and ammonium fluoride in the ratio of 1: 1: 7.   7. Method according to any one of claims I to 3 characterized in that Li2O or LiNO3 is mixed with XCabinet Beau de Lomenie Dammonium hydrogen phosphate and ammonium fluoride in the ratio of 1: 1: 7 and the mixture is heated at 200 C continuously for 12 h in an electric oven to obtain LiPF6.   8. Method according to any one of claims 1 to 3 5 characterized in that Li2CO3 or Li2O or LiNO3 is mixed with diammonium phosphate in the ratio of 1: 1, then the product is mixed with NH4F in the ratio of 1 : 7 and heated.   9. Method according to any one of the preceding claims, characterized in that the temperature is maintained between 150 10 and 350 C for the preparation of LiPF6 when LiNO3 or Li2O is the starting product.   10. Method according to any one of claims 1 to 6 characterized in that in the case of Li2CO3, the heating temperature with (NH4) 2HPO4 is about 600 C, then mixed with NH4F and heated, the temperature being maintained between 150 and 350 C.   11. Method according to any one of the preceding claims, characterized in that the reactions are carried out in the solid state.   12. Method according to any one of the preceding claims, characterized in that it comprises a two-step reaction as follows: (a) 300 C 2 (NH4) 2HP04 + Li2O -> 2 LiPO3 + 4NH3 + 3H20 600 C 2 (NH4) 2HP04 + Li2CO3 -> 2 LiPO3 + 4NH3 + C02 + 3H20 300 C 2 (NH4) 2HP04 + 2 LiNO3 -> 2 LiPO3 + 4NH3 + 2N02 + 2H20 + 02 30> 150-300 C (b) LiPO3 + 6NH4F - LiPF6 + 6NH3 + 3H20 13. Process according to any one of Claims 1 to 11, characterized in that the reaction is carried out according to a one-step process at a temperature of 150 to 300 C as follows: Li2O + 2 (NH4) 2HP04 + 12 NH4F ---> 2 LiPF6 + 16NH3 + 9H20 Li2CO3 + 2 (NH4) 2HPO4 + 12 NH4F -> 2 LiPF6 + 16NH3 + CO2 + 9H20 LiNO3 + 2 (NH4) 2HPO4 + 12 NH4F -> 2 LiPF6 + 16NH3 + NO2 + 9:20 AM 14. Method according to any one of claims 1 to 5 characterized in that dry Li20 or Li2CO3 or LiNO3 is mixed with twice its amount of diammonium phosphate, that is to say in the molar ratio of 1: 2, and the mixture is heated in an electric or muffle furnace for 6 h at a temperature of 600 C continuously in the case of Li2CO3 and approximately 300 C in the case of Li20 and LiNO3.1e product is dried at 80 C and then allowed to react with NH4F in the molar ratio of 1:> 6 to 8 for 4 h in a continuous electric oven at a temperature of the order of 150 to 350 C.   15. Method according to any one of the preceding claims, characterized in that all the materials are in the solid state.   16. Method according to any one of the preceding claims, characterized in that an electric oven is used.   17. Method according to any one of claims 1 to 15 characterized in that one uses a muffle furnace.   18. Method according to any one of claims 1 to 11 characterized in that the reaction is carried out in a single step 20 as follows:> 150-300 C UP03 + 6NH4F ---> LiPF6 + 6NH3 + 3H20