WO2015028346A1

WO2015028346A1 - Production of metal difluorophosphates in an inorganic solvent

Info

Publication number: WO2015028346A1
Application number: PCT/EP2014/067622
Authority: WO
Inventors: Carsten Brosch; Andreas Grossmann; Ulrich Seseke-Koyro; Marc Lacroix
Original assignee: Solvay Sa
Priority date: 2013-08-28
Filing date: 2014-08-19
Publication date: 2015-03-05

Abstract

The present invention relates to a method for the production of metal difluorophosphates, specifically to the production of LiPO₂F₂, in an inorganic solvent. More specifically, it relates to a method for the production of metal difluorophosphates comprising a step of reacting a phosphorus-containing reactant selected from the group consisting of phosphorus pentafluoride (PF₅),phosphoryl fluoride (POF₃), and mixtures thereof, with a metal orthophosphate, bicarbonate or carbonate in an inorganic solvent, preferably in an excess of the phosphorus-containing reactant.

Description

Production of metal difluorophosphates in an inorganic solvent

This application claims priority to European applications No. 13182079.7, filed August 28, 2013 and No. 14153455.2, filed January 31 , 2014, the whole content of these applications being incorporated herein by reference for all purposes.

The present invention relates to a method for the production of metal difluorophosphates, specifically to the production of L1PO₂F₂, in an inorganic solvent. More specifically, it relates to a method for the production of metal difluorophosphates comprising a step of reacting a phosphorus-containing reactant selected from the group consisting of phosphorus pentafluoride (PF₅), phosphoryl fluoride (POF₃), and mixtures thereof, with a metal orthophosphate, bicarbonate or carbonate in an inorganic solvent, preferably in an excess of the phosphorus-containing reactant.

Metal difluorophosphates are useful compounds in electrolyte

compositions for metal ion batteries. As a specific example, lithium

difluorophosphate, L1PO₂F₂, is useful as electrolyte salt or additive for an electrolyte composition used in lithium ion batteries.

WO 2012/016924 describes the reaction of solid L1₃PO₄ with gaseous POF₃ and/or PF₅ to yield LiP0₂F₂. Furthermore, WO 2012/016924 outlines the possibility of performing the process in presence of an aprotic organic solvent.

Now therefore, the invention makes available an improved process for the production of metal difluorophosphates, specifically for the production of L1PO₂F₂ in a technically feasible and economical manner. It is an object of the present invention to provide a process for the production of metal difluorophosphates, specifically for the production of L1PO₂F₂, which is advantageous in terms of the overall yield, the purity, the physicochemical properties including but not limited to the crystallinity and/or density of the product, the energy consumption, the safety requirements, the ease of work-up, and/or the side-product profile. Furthermore, it is an object of the present invention to provide L1PO₂F₂ in a form which is advantageous in terms of stability, solubility, crystallinity, dissolution rate, and/or ease of handling.

This object and other objects are achieved by the invention as outlined in the patent claims. Brief description of the drawing

Figure 1 shows the XRD pattern of L1PO2F2 produced according to the procedure of example 1.

Accordingly, one embodiment of the present invention is a process for the production of a compound of general formula MPO₂F₂, wherein M is Li, Na or K; comprising a reaction step (I) of a compound of the general

formula M₃PO₄, M₂CO₃, MHCO₃ or a mixture thereof, wherein each M is defined as above; with a phosphorous-containing reactant selected from the group consisting of POF₃, PF₅ and a mixture thereof; to form the compound of general formula MPO₂F₂, wherein the reaction is performed in the presence of an inorganic solvent. The inventive process is not limited to the metals M as given above. It can also be used to produce metal difluorophosphates of other metals like Mg, Zn, Ca, Sr, Ba, or Fe.

In a preferred embodiment, M is Li. In a more preferred embodiment, the reaction is the reaction of L1₃PO₄ with POF₃ to form L1PO₂F₂. Accordingly,

L1PO₂F₂ is produced by the reaction of phosphoryl fluoride (POF₃) and lithium orthophosphate (L1₃PO₄) following the reaction scheme:

2POF₃ + L13PO4 -> 3 L1PO2F2

The term "solvent" is intended to denote a chemical compound which is a liquid under the reaction conditions of reaction step (I) and in which at least part of the starting materials, reactants and/or reaction products is dissolved during the performance of reaction step (I).

The term "inorganic" is intended to denote any compound that lacks both carbon and hydrogen atoms.

Suitable examples of inorganic solvents include carbon monoxide, carbon dioxide, hydrogen fluoride, urea, POF₃, PF₅ and mixtures thereof. Although some of the aforementioned inorganic solvents are solid or gaseous under ambient conditions, they fall under the definition "inorganic solvent" as used in the context of this invention when in the liquid state under the reaction conditions of reaction step (I). In one preferred embodiment, supercritical CO₂ is used as the inorganic solvent. In another preferred embodiment the

phosphorous-containing reactant according to this invention is used as the inorganic solvent, more preferably POF₃ is used as the inorganic solvent. Thus, one compound can serve both the roles of the phosphorous-containing reactant as well as the inorganic solvent. Preferably, the initial molar ratio of POF₃ to L1₃PO₄ is equal to or greater than 1 and equal to or lower than 3. Also preferably, the phosphorous-containing reactant is used in an excess molar ratio. In case of the reaction of L1₃PO₄ with POF₃, the preferred molar ratio of POF₃ to L1₃PO₄ is equal to or greater than 2, more preferably equal to or greater than 5. Alternatively, the ratio is suitably chosen to create a liquid phase of POF₃ under the given reactor volume at room temperature.

Phosphoryl fluoride (POF₃) can be obtained commercially, e.g. from ABCR GmbH & Co. KG, or can be prepared by a known process in the art. For example, POF₃ can be prepared by fluorination of phosphoryl chloride with HF and/or other fluorinating agents, for example, ZnF₂. Alternatively, it may be also prepared by the reaction of H3PO4/P2O5, HF/H₂0 and SO3/H2SO4. Sometimes, the POF₃ obtained may contain PF₅ as impurity, or vice versa, PF₅ may comprise POF₃ as impurity. The advantage of the process of the invention is that even such mixtures can be applied without impact on the yield.

PF₅ may be obtained commercially, e.g. from Praxair, or it may be prepared from PCI₅ and HF or, as described in EP-A-0816287, for example

L1₃PO₄ is commercially available, e.g. from Strem Chemicals, Inc, Newburyport, USA, or from Chemetall GmbH, Germany. It is a solid with a melting point far above 1000°C.

Preferably, the reaction between PF₅ and L1₃PO₄, between POF₃ and L1₃PO₄ and between mixtures of POF₃ and PF₅, respectively, and L1₃PO₄ is performed in the absence of water or moisture. It is preferred to perform the reaction in apparatus made from steel or other materials resistant against corrosion, e.g. in reactors made of or clad with Monel metal and/or

Fluorpolymer (Teflon^®) coated.

L1₃PO₄ is preferably applied in the form of small particles, e.g. in the form of a powder. If desired, it can be dried before introducing it into the reaction.

The reaction conditions are chosen in a way that at least part of the inorganic solvent is in the liquid state. To this end it is preferred that the reaction is performed under a pressure of equal to or higher than 6 bar, preferably equal to or higher than 8 bar, more preferably equal to of higher than 10 bar. Also preferably, the reaction is performed at a pressure of equal to or below 20 bar, more preferably equal to or below 15 bar. Also preferably, the reaction is performed at a reaction temperature from 0 to 95 °C, preferably from 15 to 80°C, more preferably from 20 to 65 °C.

The reaction time is selected such that the desired degree of conversion is achieved. Often, a reaction time of 1 second to 5 hours gives good results for the reaction between POF₃, PF₅ and any mixtures thereof with L1₃PO₄. For the reaction between POF₃ and L1₃PO₄, a preferred reaction time of 0.5 to 5 hours gives good results. For the reaction between PF₅ or mixtures of PF₅ and POF₃ and L1₃PO₄, a preferred reaction time of 0.5 to 2 hours, most preferably of around 1 hour gives good results, too. The reaction speed is generally very fast.

In case the inorganic solvent is gaseous under ambient conditions, the inorganic solvent can be removed after reaction step (I) by venting the reaction vessel. The crude product thus obtained may optionally be treated further to remove residual reactant, inorganic solvent or by-products. To this end, the crude product may optionally be purged with a stream of nitrogen, subjected to elevated temperatures and/or subjected to reduced pressure.

In a preferred embodiment, the inorganic solvent can be recycled after the reaction step (I). If POF₃ is used as the inorganic solvent it can be removed from the reaction vessel in gaseous form by lowering the pressure in the reaction vessel, collected in a further suitable vessel and re-used for a subsequent reaction step. The inorganic solvent can optionally be purified before being re-used.

Purification and/or crystallization of L1PO₂F₂ in aprotic organic solvents have been described in the prior art. Surprisingly, it has now been found that a compound of general formula MPO₂F₂, preferably L1PO₂F₂, can be purified by recrystallisation of the compound from a pro tic organic solvent, preferably from an alcohol, more preferably from methanol. Thus, another preferred

embodiment is a process comprising a further reaction step (II) wherein the crude reaction product from reaction step (I) is dissolved in a solvent mixture comprising a protic solvent, preferably comprising an alcohol, more preferably comprising methanol. Subsequently, the product may be isolated by means of spray drying, evaporation of the solvent, crystallisation, lyophilization or a mixture thereof, preferably by means of crystallisation. If a crystallisation step is performed, this step can be performed using cold crystallisation, anti-solvent crystallisation, seeding or a mixture of these technologies.

The term "protic solvent" is intended to denote a solvent that has a hydrogen atom bound to an oxygen atom (as in a hydroxyl group) or a nitrogen atom (as in an amine group). The mixture obtained after the reaction step (I) and/or (II) can be too acidic possibly leading to a product of lower quality after isolation. Thus, in another preferred embodiment the mixture obtained after the reaction step (I) and/or (II) is subjected to a neutralization step. Preferably, the neutralization step is performed in the presence of L1₂CO₃. To this end, the neutralization agent, preferably a carbonate or bicarbonate, more preferably lithium carbonate, is added to the mixture after the reaction step (I) and/or (II), preferably added in solid form to a solution or slurry of the crude product from reaction step (I) in a suitable solvent, preferably in methanol. Advantageously, the pH of the mixture after the neutralization step is from 4 to 7, preferably from 5.5 to 6.5, more preferably about 6.

Another embodiment of the present invention concerns a process for the production of a compound of the general formula MPO₂F₂, wherein M is Li, Na or K, comprising a reaction step (I) of a compound of general formula M₃PO₄, M₃PO₄, M₂CO₃, and MHCO₃, or a mixture thereof, wherein each M is defined as above, with POF₃, PF₅ or a mixture thereof, to form the compound of general formula MPO₂F₂, wherein the reaction is performed in the presence of an organic solvent, preferably in an organic solvent in which the compound of general formula MPO₂F₂ has a solubility of > 1 g/1 at ambient conditions, preferably of > 5 g/1, more preferably of > 10 g/1. The process is not limited to the metals M as given above. It can also be used to produce metal difluorophosphates of other metals like Mg, Zn, Ca, Sr, Ba, or Fe.

In a preferred embodiment, M is Li. In a more preferred embodiment, the reaction is the reaction of L1₃PO₄ with POF₃ to form L1PO₂F₂.

The term "organic solvent" is intended to denote any compound comprising at least one carbon atom that is liquid under the reaction conditions. Advantageously, the organic solvent does not react with any of the starting materials or the reaction product. Useful examples of an organic solvent are aprotic organic solvents, for example cyclic and acyclic ethers, esters, ketones, carbonates, nitriles, sulfones and mixtures thereof wherein the solubility of the compound of general formula MPO₂F₂ is > 1 g/1 at ambient conditions.

Examples of useful organic solvents include acetone, acetonitrile,

dimethylformamide, sulfolane.

The term "ambient conditions" is intended to denote conditions referring to the standard ambient temperature and pressure (25°C, 100 kPa). The term "solubility" is intended to denote the analytical composition of a saturated solution expressed as a proportion of a designated solute in a designated solvent according to IUPAC definition.

In a preferred embodiment, the organic solvent is a diether or a poly ether, more preferably a diether, most preferably the diether is 1,2 dimethoxy ethane. The term "diether" is intended to denote a compound comprising two moieties of the structural motif "C-O-C", i.e. a compound comprising two oxygen atoms each directly connected to two groups selected from alkyl, alkylene, (hetero)aryl or (hetero)arylene. The term "polyether" is intended to denote a compound comprising at least three moieties of the structural motif "C-O-C",

i.e. a compound comprising at least three oxygen atoms each directly connected to two groups selected from alkyl, alkylene, (hetero)aryl or (hetero)arylene. The diether and/or polyether can advantageously be substituted, for example substituted by fluorine. The diether and/or polyether can advantageously be cyclic or acyclic. Useful examples of diethers are 1,2-diethoxyethane. Useful examples of polyethers are glymes of the general

formula CH₃0(CH₂CH₂0)_nCH₃ with n > 1 or crown ethers, for

example 12-crown-4, 15-crown-5, 18-crown-6, dibenzo-18-crown-6. Most preferably, the organic solvent is 1,2-dimethoxyethane.

The inventive process yields LiP0₂F₂ with superior characteristics, especially in terms of crystallinity and/or purity. Thus, another aspect of the present invention concerns LiP0₂F₂ obtainable using the inventive process as described above.

Yet another aspect of the present invention concerns crystalline LiP0₂F₂ characterized by an X-ray powder diffraction pattern showing the two strongest peaks at 22.6 ± 0.2 and 27.3 ± 0.2 ⁰ 2-Theta, preferably characterized by an X-ray powder diffraction pattern showing the four strongest peaks at 19.9 ± 0.2, 20.6 ± 0.2, 22.6 ± 0.2, 27.3 ± 0.2 ⁰ 2-Theta.

Still another aspect of the present invention concerns crystalline LiP0₂F₂ characterized by an X-ray powder diffraction pattern essentially as shown in Figure 1.

A further aspect concerns crystalline LiP0₂F₂ characterized by a bulk density of < 500 g/1, preferably between 100 and 400 g/1, more preferably between 200 and 300 g/1.

Yet another aspect of the present invention concerns an electrolyte composition for lithium-ion batteries, lithium- sulfur batteries and/or lithium- oxygen batteries comprising the crystalline L1PO₂F₂ according to this invention and further comprising a solvent suitable for electrolyte solutions for lithium-ion batteries, lithium- sulfur batteries and/or lithium-oxygen batteries.

Solvents suitable for electrolyte solutions for lithium- ion batteries, lithium- sulfur batteries and/or lithium-oxygen batteries are known in the art. Suitable examples include the group of dialkyl carbonates (which are linear) and alkylene carbonates (which are cyclic), and wherein the term "alkyl" denotes preferably CI to C4 alkyl, the term "alkylene" denotes preferably C2 to C7 alkylene groups, including a vinylidene group, acetone, acetonitrile, linear dialkyl carbonates, e.g. dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, cyclic alkylene carbonates, e.g. ethylene carbonate, propylene carbonate, and vinylidene carbonate, and fluorinated derivatives of the compounds mentioned in this paragraph, e.g. l-fluoroethyl methyl carbonate, 4-fluoroethylene carbonate or l-fluoroethyl allyl carbonate.

The concentration of the metal difluorophosphates of the invention in the electrolyte solution is preferably 1 ± 0.2 molar. Often, the electrolyte solution may comprise LiPF₆ and L1PO2F2. In the case, the combined concentration of the two compounds in the electrolyte solution is preferably 1 ± 0.2 molar.

Should the disclosure of any of the patents, patent applications, and publications that are incorporated herein by reference be in conflict with the present description to the extent that it might render a term unclear, the present description shall take precedence.

Examples

Example 1 : Production of LiPOiFi

The reactor is charged with L1₃PO₄ (5.8 kg, 50 mol) and cooled to 16°C.

POF₃ (35.5 kg, 350 mol) is fed to a pressure of 14 bar(g) in the reactor while agitating the L1₃PO₄. During addition of the POF₃ the temperature rises continuously to 60°C. After 16 h, the excess POF₃ is pumped off and can be recycled for the next batch. The reactor (double jacket) is then heated to 140°C to evaporate residual gas while under vacuum with an additional purge of 300 1/h nitrogen for 24 h. Subsequently, the reactor is cooled to room temperature and 38 kg MeOH is added. The solution is being processed by filtration through a 5 μιη Teflon^® sieve.

The filtrate can be further treated by either

(A) Being transferred to a evaporation unit to produce crude L1PO₂F₂ in form of crystals. The crystals can be transferred to a glove box and milled to a fine powder, which again is vacuum dried (100 °C and 100 mbar using a flow of nitrogen of 100 1/h) to remove residual solvent from the crystallization step. The accumulated yield is 85 %.

or

(B) Being spray dried under controlled and ex-proof condition, which results also in a 85 % yield of LiP0₂F₂.

Analytical data

PXR (powder X-ray diffraction): Samples were analysed on a Broker AXS D8 Advance powder X-ray diffractometer. The wavelength of the radiation was 1.5406Λ.

Measurement conditions were as follows.

Position [° 2 Theta] Intensity [counts] Position [° 2 Theta] Intensity [counts]

13,03 538,88 46,08 310,03

19,91 7900, 17 46,52 101 1 ,01

20,64 9222,67 46,89 509,58

21 ,37 1732,4 47,55 1897,22

21 ,78 2100,5 48,29 272,25

22,55 17484,82 50,88 588, 15

23,32 631 ,65 51 ,81 479,78

26,27 2304,76 53,45 560,08

27,31 16984,9 54,33 464,72

27,86 6620,6 55, 12 674,57

28,45 729, 1 1 56,35 306,58

29,59 439,26 57,41 269,72

30,56 1769,7 57,72 302,43

32,25 885,48 59,08 343,91

32,51 1351 ,54 59,66 203,39

33,90 2813,27 60,61 544,44

35,42 426,98 62,45 340,32

37,64 245, 17 67,40 246,56

38, 13 1005,28 68,07 288,53

38,67 394,43 69,21 269,34

39,53 381 ,03 69,72 167,86

40,46 1695,09 71 ,07 206,26

42,01 549,94 71 ,84 280, 12

43,51 344,46 73,04 151 ,94

44,94 446,99

Table 1 : XRD data for the compound according to example 1(B)

¹⁹F-NMR (470.94 MHz; D₆-acetone): -84.25 ppm (doublet, J= 926 Hz) The bulk density at ambient conditions of the L1PO₂F₂ according to example 1 was determined to be 280 g/1. In a comparable example, the bulk density of the L1PO₂F₂ prepared according to example 3 of WO 2012/016924 was determined to be 560 g/1.

Example 2 : Production of LiPOiFi

58 g Li₃P04 was dried at 200°C for 18 h and subsequently placed in a Teflon^® reactor equipped with a paddle mixer and a Teflon^® condenser. Dimethoxy ethane (500 ml) was added and the mixture was stirred at 200 rpm. The reaction vessel was subjected to a nitrogen atmosphere and subsequently, POF₃ (103.4 g) was introduced into the mixture via an immersion tube at room temperature over a period of 4.5 h. After the introduction of POF₃ was completed, reaction mixture and vessel were flushed with nitrogen gas for 30 min. 25 g lithium carbonate was added and stirring continued for another 10 min. The mixture was filtered through a 10 μιη Teflon^® filter with suction (300 mbar on the filtrate side). The filtrate showed pH 6. Volatiles were removed by means of a spray dryer (Buechi B-295- Inert Loop) under the following conditions: inlet temperature 202°C, outlet temperature 115°C, feed rate 7 g/min.

The crude product is dried at 100°C and 100 mbar using a flow of nitrogen of 100 1/h for 18 h to yield 146 g (90 %) of the product.

Example 3 : Electrolyte solution for lithium ion batteries, lithium sulfur batteries and/or lithium-oxygen batteries

117 g LiPF₆, 23 g LiP0₂F₂ (obtained analogously to example 1),

50 g 4-fluoroethylene carbonate and propylene carbonate are mixed in amount such that a total volume of 1 liter is obtained. The resulting solution contains 0.77 mol LiPF₆ and 0.23 mol LiP0₂F₂.

Claims

C L A I M S

1. A process for the production of a compound of general

formula MPO₂F₂, wherein M is Li, Na or K; comprising a reaction step (I) of a compound of the general formula M₃PO₄, M₂CO₃, MHCO₃ or a mixture thereof, wherein each M is defined as above; with a phosphorous-containing reactant selected from the group consisting of POF₃, PF₅ and a mixture thereof; to form the compound of general formula MPO₂F₂, wherein the reaction is performed in the presence of an inorganic solvent.

2. The process according to claim 1 wherein M is Li.

3. The process according to claim 1 or 2 comprising the reaction step (I) is the reaction of L1₃PO₄ with POF₃ to form L1PO₂F₂.

4. The process according to any one of claims 1 to 3 wherein the reaction is performed under a pressure of equal to or higher than 6 bar, preferably equal to or higher than 8 bar, more preferably equal to of higher than 10 bar.

5. The process according to any one of claims 1 to 4 wherein the reaction is performed at a reaction temperature from 0 to 100°C, preferably from 10 to 70°C.

6. The process according to any one of claims 1 to 5 wherein the phosphorous-containing reactant is used as the inorganic solvent, preferably POF₃ is used as the inorganic solvent.

7. The process according to any one of claims 1 to 6 wherein the phosphorous-containing reactant is used in an excess molar ratio.

8. The process according to any one of claims 1 to 6 wherein the reaction is performed in excess POF₃.

9. The process according to claim 8 wherein the excess POF₃ is recycled.

10. The process according to any one of claims 1 to 9 comprising a further reaction step (II) wherein the crude reaction product from reaction step (I) is dissolved in a solvent mixture comprising an alcohol, preferably comprising methanol.

11. L1PO₂F₂ obtainable using the process according to any one of claims 1 to 10.

12. Crystalline L1PO₂F₂ characterized by an X-ray powder diffraction pattern showing the two strongest peaks at 22.6 ± 0.2 and 27.3 ± 0.2 ⁰ 2-Theta.

13. The crystalline L1PO₂F₂ according to claim 12 characterized by an X-ray powder diffraction pattern showing the four strongest peaks at 19.9 ± 0.2, 20.6 ± 0.2, 22.6 ± 0.2, 27.3 ± 0.2 ⁰ 2-Theta.

14. Crystalline L1PO₂F₂ characterized by an X-ray powder diffraction pattern essentially as shown in Figure 1.

15. An electrolyte composition for lithium- ion batteries, lithium-sulfur batteries and/or lithium-oxygen batteries comprising the crystalline L1PO₂F₂ according to any one of the claims 11 to 14 and further comprising a solvent suitable for electrolyte composition for lithium-ion batteries, lithium-sulfur batteries and/or lithium-oxygen batteries.