EP2900593A1

EP2900593A1 - Production of high-purity lithium difluorophosphate

Info

Publication number: EP2900593A1
Application number: EP13766577.4A
Authority: EP
Inventors: Matthias Boll; Wolfgang Ebenbeck
Original assignee: Lanxess Deutschland GmbH
Current assignee: Lanxess Deutschland GmbH
Priority date: 2012-09-28
Filing date: 2013-09-27
Publication date: 2015-08-05
Also published as: US20150263384A1; CA2884406A1; WO2014049156A1; JP2015533767A; KR20150063051A; CN104684845A; EP2712843A1

Abstract

The present invention relates to a process for producing high-purity lithium difluorophosphate in particular having low sodium content and in particular taking the form of solutions thereof in organic solvents, starting from lithium fluoride and phosphorus pentafluoride.

Description

Preparation of high purity lithium difluorophosphate

The present invention relates to a process for the preparation of high-purity, in particular sodium-poor, limium difluorophosphate, in particular in the form of its solutions in organic solvents, starting from lithium fluoride and phosphorus pentafluoride. The proliferation of portable electronic devices, such as laptops and palmtop computers, cell phones or video cameras, and thus the need for lightweight and powerful batteries and accumulators has dramatically increased in recent years worldwide. In addition, there will be the equipment of electric vehicles with such accumulators and batteries in the future. Limium difluorophosphate (LiP0 ₂ F ₂ ) has aroused industrial interest in particular as an alternative, because fairly stable conductive salt to Lithiumhexafluorophosphat in the production of high-performance accumulators. In order to ensure the functionality and lifetime and thus the quality of such accumulators, it is of particular importance that the lithium compounds used are highly pure and in particular contain as low as possible amounts of other metal ions, in particular sodium or potassium ions. Foreign metal ions are believed to be responsible for cell shedding due to precipitate formation (US 7,981,388). High levels of chloride are held responsible for corrosion.

From the prior art, only a few processes for the preparation of Limiumdifluorphosphat are known. WO 2012/004188 A discloses a process in which tetraphosphorodecoxide (P ₄ O ₁₀ ) is reacted with lithium fluoride (LiF) at temperatures of about 300 ° C. to form limium difluorophosphate.

WO 2008/111367 A discloses a process in which chlorides and bromides are reacted with lithium hexafluorophosphate and water.

EP 2 061 115 discloses a process in which lithium hexafluorophosphate is partially hydrolyzed with water in the presence of siloxanes to give limium difluorophosphate and lithium tetrafluorophosphate.

All methods have in common that they either run nonspecifically with respect to their target products or produce large amounts of inevitable by-products. The prior art shows that it is technically very complex to achieve high purities for Lithiumdifluorphosphat and in particular to keep the content of foreign metal ions and the content of chloride low. Consequently, not every purity requirement can be met with the hitherto known processes for the preparation of lithium difluorophosphate. Accordingly, it was an object of the present invention to provide an efficient process for producing high purity limium difluorophosphate or high purity solutions containing lithium difluorophosphate in organic solvents, which does not require elaborate purification operations and yields high yields.

The solution to the problem and object of the present invention is now a process for the preparation of Lithiumdifluorphosphat comprising at least the step: a) contacting solid lithium fluoride with a gas containing phosphorus pentafluoride wherein the solid lithium fluoride has a water content of more than 1,500 ppm, preferably 1,550 ppm or more more preferably 1550 ppm to 100,000 ppm, even more preferably 2,000 ppm to 20,000 ppm, and most preferably 5,000 ppm to 15,000 ppm.

If solutions of limium difluorophosphate are to be prepared in organic solvent, the following steps are preferably followed by at least b) contacting the reaction mixture formed according to a) containing limium difluorophosphate with an organic solvent, the formed limium difluorophosphate at least partially dissolving

c) optionally but preferably separation of solid components from the solution containing lithium hexafluorophosphate.

It should be noted at this point that the scope of the invention includes all possible and possible combinations of the above-listed and listed below, general or preferred ranges mentioned components, value ranges or process parameters.

In step a), solid lithium fluoride containing the above-specified water content is contacted with a gas containing phosphorus pentafluoride to obtain a reaction mixture containing lithium difluorophosphate and unreacted lithium fluoride. The lithium fluoride used in step a) has, for example, a purity of 98.0000 to 99.9999% by weight, preferably 99.0000 to 99.9999% by weight, more preferably 99.9000 to 99.9995% by weight. , particularly preferably 99.9500 to 99.9995% by weight and very particularly preferably 99.9700 to 99.9995% by weight, based on anhydrous product. The lithium fluoride used furthermore preferably has foreign ions:

1) a content of 0, 1 to 250 ppm, preferably 0, 1 to 75 ppm, more preferably 0, 1 to 50 and particularly preferably 0.5 to 10 ppm and most preferably 0.5 to 5 ppm of sodium in ionic form and

2) a content of 0.01 to 200 ppm, preferably 0.01 to 10 ppm, more preferably 0.5 to 5 ppm and particularly preferably 0.1 to 1 ppm of potassium in ionic form.

The lithium fluoride used furthermore preferably has foreign ions

3) a content of 0.05 to 500 ppm, preferably 0.05 to 300 ppm, more preferably 0.1 to 250 ppm and particularly preferably 0.5 to 100 ppm of calcium in ionic form and / or

4) a content of 0.05 to 300 ppm, preferably 0.1 to 250 ppm and more preferably 0.5 to 50 ppm of magnesium in ionic form.

The lithium fluoride used furthermore has, for example, foreign ions

i) a content of 0, 1 to 1000 ppm, preferably from 0, 1 to 100 ppm and more preferably 0.5 to 10 ppm of sulfate and / or

ii) a content of 0.1 to 1000 ppm, preferably 0.5 to 500 ppm chloride,

also based on the anhydrous product and it is true that the sum of lithium fluoride and the aforementioned foreign ions does not exceed 1,000,000 ppm based on the total weight of the technical lithium carbonate based on the anhydrous product.

In one embodiment, the lithium fluoride contains a total of foreign metal ion content of 1000 ppm or less, preferably 300 ppm or less, more preferably 20 ppm or less, and most preferably 10 ppm or less.

Contacting solid lithium fluoride containing the above specified water content with a gas containing phosphorus pentafluoride to yield a reaction mixture containing lithium difluorophosphate and unreacted lithium fluoride can be accomplished by any method known to those skilled in the gaseous solid state art. For example, the contacting may take place in a fixed bed or a fluidized bed, wherein the contacting in a fluidized bed is preferred. In one embodiment, the fluidized bed may be configured as a stirred fluidized bed. The solid lithium fluoride used can, in particular when used as a fixed bed, for example in the form of shaped articles or in the form of fine particles, for example in the form of a powder are used, the use of fine particles or powders, in particular for use fluidized bed is preferred. When using moldings, preference is given to those which have a solids content in the range from 20 to 95% by weight, preferably in the range from 60 to 90% by weight, particularly preferably at 67 to 73% by weight and very particularly preferably approx. 70 wt .-% is.

Shaped bodies can in principle be in any desired form, with spherical, cylindrical or annular shaped bodies being preferred. Preferably, the shaped bodies are not larger than 3 cm in any dimension, preferably not larger than 1.5 cm.

Shaped bodies are produced, for example, by extrusion from a mixture of lithium fluoride and water, the shaped bodies being dried after extrusion at temperatures of from 50 to 200 ° C., preferably at temperatures of from 80 to 150 ° C., particularly preferably at about 120 ° C. they have the above specified water content. Such shaped bodies are typically cylindrical.

Water contents are, unless stated otherwise, determined by the method according to Karl Fischer, which is known to the person skilled in the art and described, for example, in P.Bruttel, R. Schlink, "Water Determination by Karl Fischer Titration", Metrohm Monograph 8.026.5001, 2003 The reaction kinetics in step a) depend on the reaction temperature, the effective surface area of the lithium fluoride, the water content, the flow resistance caused by the fixed bed or fluidized bed, and the flow velocity, without the applicant intending to be scientifically exact While the temperature, pressure and flow rate can be controlled in terms of process technology, the effective surface area of the lithium fluoride, the flow resistance and the volume increase of the reaction mixture depend on the morphology of the lithium fluoride used.

It has been found that it is advantageous both for use in the production of moldings and for use in the form of fine particles, lithium fluoride having a D50 value of 4 to 1000 μπι, preferably 15 to 1000 μπι, more preferably 15 to 300 ppm , Particularly preferably 15 to 200 μπι and even more preferably 20 to 200 μπι use. The lithium fluoride used furthermore preferably has a D10 value of 0.5 μm or more, preferably 5 μm or more, more preferably 7 μm or more. In another embodiment, the lithium fluoride has a DlO value of 15 μιη or more.

By the D50 value or the D10 value is meant the particle size in and below which a total of 10% by volume and 50% by volume of the lithium fluoride are present.

The lithium fluoride further preferably has a bulk density of 0.6 g / cm ³ or more, preferably 0.8 g / cm ³ or more, more preferably 0.9 g / cm ³ or more, and particularly preferably 0.9 g / cm ³ to 1.2 g / cm ³ .

The lithium fluoride having the aforementioned specifications can be obtained, for example, by a process comprising at least the following steps: i) providing an aqueous medium containing dissolved lithium carbonate

ii) reacting the aqueous medium provided according to a) with gaseous hydrogen fluoride to form an aqueous suspension of solid lithium fluoride

iii) separating the solid lithium fluoride from the aqueous suspension

iv) drying the separated lithium fluoride to the above specified water content.

According to step i), an aqueous solution containing lithium carbonate is provided.

The term "aqueous medium containing dissolved lithium carbonate" is to be understood here as meaning a liquid medium which

i) contains dissolved lithium carbonate, preferably in an amount of at least 2.0 g / 1, more preferably 5.0 g / 1 to the maximum solubility in the aqueous medium at the selected temperature, most preferably 7.0 g / 1 to maximum solubility in the aqueous medium at the selected temperature. In particular, the content of lithium carbonate is 7.2 to 15.4 g / l. It is known to the skilled person that the solubility of lithium carbonate in pure water at 0 ° C 15.4 g / 1 at 20 ° C 13.3 g / 1, at 60 ° C 10.1 and at 100 ° C 7.2 g / 1 and consequently certain concentrations only in certain cases

Temperatures can be reached

ii) contains at least 50% by weight of water, preferably 80% by weight, more preferably at least 90% by weight, based on the total weight of the liquid medium, and

iii) preferably also solids-free or has a solids content of more than 0.0 to 0.5 wt .-%, preferably solids-free or a solids content of more than 0.0 to 0.1 % By weight, more preferably solids-free or has a solids content of more than 0.0 to 0.005 wt., And particularly preferably solids-free,

wherein the sum of components i), ii) and preferably iii) is at most 100% by weight, preferably 98 to 100% by weight and particularly preferably 99 to 100% by weight, based on the total weight of the aqueous medium containing dissolved lithium carbonate ,

The aqueous medium containing dissolved lithium carbonate may in another embodiment of the invention as a further component

iv) contain at least one water-miscible organic solvent. Suitable water-miscible organic solvents are, for example, monohydric or polyhydric alcohols, such as methanol, ethanol, n-propanol, isopropanol, n-butanol, ethylene glycol,

Ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, propylene glycol, 1,3-propanediol or glycerol, ketones such as acetone or ethyl methyl ketone.

If the aqueous medium containing dissolved lithium carbonate contains at least one water-miscible organic solvent, their proportion may be, for example, more than 0.0% by weight to 20% by weight, preferably 2 to 10% by weight, in which case in each case in that the sum of components i), ii), iii) and iv) contains at most 100% by weight, preferably 95 to 100% by weight and particularly preferably 98 to 100% by weight, based on the total weight of the aqueous medium dissolved lithium carbonate is.

Preferably, however, the aqueous medium containing dissolved lithium carbonate is free of water-miscible organic solvents.

The aqueous medium containing dissolved lithium carbonate may contain as further component v) a complexing agent, preferably in an amount of 0.001 to 1 wt .-%, preferably 0.005 to 0.2% by weight based on the total weight of the aqueous medium containing dissolved lithium carbonate.

Complexing agents are preferably those whose complexes with calcium ions and magnesium ions form complexes which have a solubility of more than 0.02 mol / l at a pH of 8 and 20 ° C. Examples of suitable complexing agents are ethylenediaminetetraacetic acid (EDTA) and its alkali metal or ammonium salts, with ethylenediaminetetraacetic acid being preferred.

In one embodiment, however, the aqueous medium containing dissolved lithium carbonate is free of complexing agents.

To provide the aqueous solution containing lithium carbonate, the procedure is preferably such that solid lithium carbonate is brought into contact with a lithium carbonate-free or lithium carbonate-poor aqueous medium, so that the solid Lithium carbonate at least partially goes into solution. A low-lithium carbonate aqueous medium is understood as meaning an aqueous medium which has a lithium carbonate content of up to 1.0 g / l, preferably up to 0.5 g / l, of lithium carbonate but is not free of lithium carbonate.

The aqueous medium used for the preparation fulfills the conditions mentioned above under ii) and iii) and optionally comprises the components iv) and v).

In the simplest case, the aqueous medium is water, preferably water with a specific electrical resistance of 5 Ω · cm at 25 ° C or more.

In a preferred embodiment, the steps i) to iv) are repeated one or more times. In this case, the aqueous medium used in the repetition for providing the aqueous medium containing dissolved lithium carbonate as lithium carbonate-free or lithium carbonate-poor aqueous medium that in a previous step iii) is obtained in the separation of solid lithium fluoride from the aqueous suspension of lithium fluoride. In this case, the lithium carbonate-free or lithium carbonate-poor aqueous medium contains dissolved lithium fluoride, typically up to the saturation limit at the respective temperature.

In one embodiment, the contacting of the lithium carbonate-free or aqueous medium with the solid lithium carbonate may be accomplished in a stirred reactor, flow-through reactor, or any other apparatus known to those skilled in the art for contacting liquid with solids. Preferably, in the sense of a short residence time and the achievement of a concentration of lithium carbonate in the aqueous medium used which is as close as possible to the saturation point, an excess of lithium carbonate is used, i. so much that complete dissolution of the solid lithium carbonate can not occur. In order to limit the solids content according to (ii) in this case, filtration, sedimentation, centrifugation or any other method known to the person skilled in the art for the separation of solids from or from liquid is then carried out, filtration being preferred. If the process steps i) to iii) are repeated and / or carried out continuously, filtration through a cross-flow filter is preferred.

The temperature when contacting can be carried out, for example, from the freezing point to the boiling point of the aqueous medium used, preferably 0 to 100 ° C, more preferably 10 ° to 60 ° C and particularly preferably 10 ° to 35 ° C, in particular 16 to 24 ° C.

The pressure when contacting can be, for example, 100 hPa to 2 MPa, 900 hPa to 1200 hPa, in particular ambient pressure is particularly preferred. In the context of the invention, technical lithium carbonate is understood as meaning lithium carbonate which has a purity of 95.0 to 99.9% by weight, preferably 98.0 to 99.8% by weight and particularly preferably 98.5 to 99.8% by weight. -% based on anhydrous product possesses.

Preferably, the technical lithium carbonate further contains foreign ions, i. ions that are not lithium or carbonate ions

1) a content of 200 to 5000 ppm, preferably 300 to 2000 and more preferably

500 to 1200 ppm of sodium in ionic form and / or

2) a content of 5 to 1000 ppm, preferably 10 to 600 ppm of potassium in ionic form and / or

3) a content of 50 to 1000 ppm, preferably 100 to 500 and particularly preferably 100 to 400 ppm of calcium in ionic form and / or

4) a content of 20 to 500 ppm, preferably 20 to 200 and particularly preferably 50 to 100 ppm of magnesium in ionic form. Furthermore, the technical lithium carbonate further contains foreign ions, i. ions which are not lithium or carbonate ions: i) a content of 50 to 1000 ppm, preferably 100 to 800 ppm of sulfate and / or ii) a content of 10 to 1000 ppm, preferably 100 to 500 ppm of chloride,

also based on the anhydrous product.

In general, the sum of lithium carbonate and the abovementioned foreign ions 1) to 4) and optionally i) and ii) does not exceed 1,000,000 ppm, based on the total weight of the technical lithium carbonate, relative to the anhydrous product.

In a further embodiment, the technical lithium carbonate has a purity of 98.5 to 99.5% by weight and a content of 500 to 2000 ppm of foreign metal ions, i. Sodium, potassium, magnesium and calcium.

In a further embodiment, the technical lithium carbonate preferably additionally has a content of 100 to 800 ppm of foreign anions, i. Sulphate or chloride based on the anhydrous product.

Unless otherwise stated, the ppm data given herein are based on parts by weight, the contents of said cations and anions being determined by ion chromatography, unless otherwise indicated in the experimental section. In one embodiment of the method according to the invention, the provision of the aqueous medium containing lithium carbonate or the contacting of a lithium carbonate-free or poor, aqueous medium with solid lithium carbonate batchwise or continuously, wherein the continuous implementation is preferred. The aqueous medium containing dissolved lithium carbonate provided according to step i) typically has a pH of 8.5 to 12.0, preferably of 9.0 to 11.5, measured or calculated at 20 ° C and 1013 hPa.

Before the aqueous medium containing dissolved lithium carbonate provided in step i) is used in step (ii), it can be passed over an ion exchanger in order, in particular, to at least partially remove calcium and magnesium ions. For example, weakly or strongly acidic cation exchangers can be used for this purpose. For use in the process according to the invention, the ion exchangers can be used in devices, such as, for example, flow columns which are filled with the cation exchangers described above, for example in the form of powders, beads or granules. Particularly suitable are ion exchangers containing copolymers of at least styrene and divinylbenzene, which also contain, for example, aminoalkylenephosphonic acid groups or iminodiacetic acid groups.

Such ion exchangers are, for example, those of the Lewatit ™ type such as Lewatit ™ OC 1060 (AMP type), Lewatit ™ TP 208 (IDA type), Lewatit ™ E 304/88, Lewatit ™ S 108, Lewatit TP 207, Lewatit ™ S 100; Amberlite ™ type such as Amberlite ™ IR 120, Amberlite ™ IRA 743; those of the Dowex ™ type, such as Dowex ™ HCR; those of the Duolite type, such as Duolite ™ C 20, Duolite ™ C 467, Duolite ™ FS 346; and Imac ™ type such as Imac ™ TMR, with Lewatit ™ types being preferred. Preferably, such ion exchangers are used, which are as low-sodium as possible. For this purpose, it is advantageous to rinse the ion exchanger before use with the solution of a lithium salt, preferably an aqueous solution of lithium carbonate.

In one embodiment of the method according to the invention, no treatment with ion exchangers takes place. According to step ii), the reaction of the aqueous medium provided according to step i) comprising dissolved lithium carbonate with gaseous hydrogen fluoride is carried out to give an aqueous suspension of solid lithium fluoride. The reaction can be carried out, for example, by introducing or passing a gaseous hydrogen fluoride-containing gas stream into or over the aqueous medium containing dissolved lithium carbonate, or by spraying, atomizing or flowing through the aqueous medium containing dissolved lithium carbonate in or through a gas containing gaseous hydrogen fluoride.

Due to the very high solubility of gaseous hydrogen fluoride in aqueous media, it is preferred to pass, spray, mist or flow through it, with pass-over being even more preferred.

Gaseous hydrogen fluoride contained as a gaseous hydrogen fluoride gas or gas containing gaseous hydrogen fluoride can be used as such or a gas containing gaseous hydrogen fluoride and an inert gas, an inert gas is to be understood as a gas that does not react with lithium fluoride under the usual reaction conditions. Examples are air, nitrogen, argon and other noble gases or carbon dioxide, with air and more nitrogen being preferred. The proportion of inert gas can vary as desired and, for example, 0.01 to 99 vol .-%, preferably 1 to 20 vol .-%.

In a preferred embodiment, the gaseous hydrogen fluoride used contains 50 ppm of arsenic in the form of arsenic compounds or less, preferably 10 ppm or less. The indicated arsenic contents are determined photometrically after conversion to arsenic hydrogen and its reaction with silver diethyldithiocarbaminate to give a red color complex (spectrophotometer, for example LKB Biochrom, Ultrospec) at 530 nm.

In a likewise preferred embodiment, the gaseous hydrogen fluoride used contains 100 ppm of hexafluorosilicic acid or less, preferably 50 ppm or less. The indicated hexafluorosilicic acid content is determined photometrically as silicomolybdic acid and its reduction with ascorbic acid to a blue color complex (spectrophotometer, e.g., LKB Biochrom, Ultrospec). Disturbing effects of fluorides are suppressed by boric acid, interfering reactions of phosphate and arsenic by the addition of tartaric acid.

In the reaction according to step ii), lithium fluoride is formed, which precipitates due to the fact that it is less soluble in the aqueous medium than lithium carbonate, and consequently forms an aqueous suspension of solid lithium fluoride. It is known to those skilled in the art that lithium fluoride has a solubility of about 2.7 g / l at 20 ° C. The reaction is preferably carried out in such a way that the resulting aqueous suspension of solid lithium fluoride reaches a pH of 3.5 to 8.0, preferably 4.0 to 7.5, and more preferably 5.0 to 7.2. Carbon dioxide is liberated at the stated pH values. In order to enable its release from the suspension, it is advantageous to pass the suspension to, for example, stirring or via static mixing elements.

The temperature in the reaction according to step ii) can be, for example, from the freezing point to the boiling point of the aqueous medium containing dissolved lithium carbonate, preferably 0 to 65 ° C., more preferably 15 ° to 45 ° C. and particularly preferably 15 ° to 35 ° C., especially 16 to 24 ° C.

The pressure in the reaction according to step ii) can be, for example, 100 hPa to 2 MPa, 900 hPa to 1200 hPa, in particular ambient pressure is particularly preferred.

In step iii), the separation of the solid lithium fluoride from the aqueous suspension. Separation is accomplished, for example, by filtration, sedimentation, centrifugation, or any other method known to those skilled in the art for separating solids from or from liquids, with filtration being preferred.

If the filtrate for step i) is used again and the process steps a) to c) are carried out repeatedly, filtration through a cross-flow filter is preferred.

The solid lithium fluoride thus obtained typically still has a residual moisture of from 1 to 40% by weight, preferably from 5 to 30% by weight. Before the lithium fluoride separated in step iii) is dried according to step iv), it can be washed once or several times with water or a medium containing water and water-miscible organic solvents. Water is preferred. Water having an electrical resistance of 15 Ω · cm at 25 ° C or more is particularly preferable. From step iii) adhering to the solid lithium fluoride water with foreign ions is thereby removed as far as possible.

In step iv), the lithium fluoride is dried. Drying can be carried out in any apparatus known to the person skilled in the art for drying, for example belt, thin-layer or conical dryers. Preferably, the drying is carried out by heating the lithium fluoride, preferably at 100 to 800 ° C, more preferably 200 to 500 ° C. Alternatively, it can be dried by microwaves. The drying can either be done so that the desired water content is achieved directly, or so that after intensive drying the lithium fluoride water is added again to the desired amount. In order to achieve a homogeneous distribution of the water on the solid lithium fluoride in this case, for example intensive mixing by grinding or stirring, or alternatively the water can also be introduced in the form of a moist gas stream.

The preparation of lithium fluoride explained in more detail with reference to FIG 1.

In a device for producing lithium fluoride 1 is solid lithium carbonate (Li ₂ C0 ₃ (s)) with water (H ₂ 0) and, if it is not the Erstbefüllung the device 1, the filtrate from the filtration unit 19 in the template 3, wherein the lithium carbonate at least partially dissolves. The suspension thus obtained is conveyed via the line 4 through the pump 5 via a filtration unit 6, which is designed here as a cross-flow filter, wherein undissolved lithium carbonate is recycled to the template 3 via line 7 and the filtrate, the aqueous medium containing dissolved Lithium carbonate is introduced via the line 8 in the reactor 9. In the reactor 9, a gas stream containing gaseous hydrogen fluoride, which in this case contains gaseous hydrogen fluoride and nitrogen, is introduced via line 10 into the gas space 11 of the reactor, which is located above the liquid space 12 of the reactor. By the pump 13, the contents of the liquid space 12, which initially consists essentially of the aqueous medium containing dissolved lithium carbonate and is converted by the reaction into a suspension containing solid lithium fluoride, passed via the line 14 to a packed column 15, in which the release of the carbon dioxide formed during the reaction is conveyed from the suspension. About the outlet 16, the carbon dioxide and the nitrogen used as a diluent is discharged. After passing through the packed column, the contents of the liquid space 12 guided out of the reactor 9 flow back into the liquid space 12 through the gas space 11. The return through the gas space 11 has the advantage that the liquid surface, in part also by passive atomization, is increased, which promotes the reaction with gaseous hydrogen fluoride. After reaching the target pH or sufficient formation of solid lithium fluoride, the resulting suspension of solid lithium fluoride is pumped by the pump 17 via line 18 to the filtration unit 19, which is designed here as a cross-flow filter. The solid lithium fluoride (LiF (s)) is recovered, the filtrate, the lithium carbonate-free or lithium carbonate poor aqueous medium is recycled via line 20 in the template 3. Since the recovered lithium fluoride has a residual content of water and water is discharged via the outlet 16 with the carbon dioxide, the supply of water (H ₂ 0) in the template 3 is essentially after the initial filling of the device 1 to compensate for the loss of water described above in further cycles.

It is clear to the person skilled in the art that foreign metal ions, in particular sodium and potassium, which form readily water-soluble carbonates and fluorides, accumulate in the circulation stream of the aqueous media. Optionally, a portion of the filtrate of the filtration unit 19 via the outlet 22 on the valve 21, which is designed here as an example as a three-way valve, be discharged.

By returning the filtrate of the filtration unit 19 in the template 3, it is possible in the Lithiumfluoridherstellung a degree of conversion of 95% or more, especially at high repetition numbers of steps a) to d), also called cycle numbers, for example, 30 or more even of 97% or more to be achieved, wherein the degree of conversion is the yield of high-purity lithium fluoride based on the lithium carbonate used.

In step a), solid lithium fluoride containing the above specified water content is contacted with a gas stream containing phosphorus pentafluoride. The phosphorus pentafluoride can be prepared in a manner known per se by a process which comprises at least the following steps.

1) Reaction of phosphorus trichloride with hydrogen fluoride to phosphorus trifluoride and

Hydrochloric

2) reaction of phosphorus trifluoride with elemental chlorine to trifluoride phosphorodichloride

3) Reaction of phosphorodichloride trifluoride with hydrogen fluoride

Phosphorus pentafluoride and hydrogen chloride

The gas mixture obtained according to step 3) can be used directly either with or without removal of the hydrogen chloride in step a) as a gas containing phosphorus pentafluoride. If particularly low chloride contents are to be realized, hydrogen chloride is at least largely removed from the gas mixture, which can be carried out by methods known per se, for example selective adsorption on basic adsorbents

Alternatively, the chloride content can be lowered by introducing inert gas such as nitrogen or argon through the reactor following the reaction of PF5 with LiF. Alternatively, the preparation of largely hydrogen chloride-free phosphorus pentafluoride by reacting Tetraphosphordecaoxid with hydrogen fluoride.

As the gas containing phosphorus pentafluoride is typically a gas mixture containing 5 to 41 wt .-% of phosphorus pentafluoride and 6 to 59 wt .-% hydrogen chloride, preferably 20 to 41 wt .-% phosphorus pentafluoride and 40 to 59 wt .-% hydrogen chloride, more preferably 33 to 41 wt .-% phosphorus pentafluoride and 49 to 59 wt .-% hydrogen chloride are used, wherein the proportion of phosphorus pentafluoride and hydrogen chloride, for example 11 to 100 wt .-%, preferably 90 to 100 wt .-% and particularly preferably 95 to 100 wt .-% is.

The difference to 100 wt .-%, if present at all, may be inert gases, wherein an inert gas is to be understood here as a gas that does not react with phosphorus pentafluoride, fluorine or hydrogen chloride or lithium fluoride under the usual reaction conditions. Examples are nitrogen, argon and other noble gases or carbon dioxide, with nitrogen being preferred.

The difference to 100 wt .-%, if any, may alternatively or additionally continue to be hydrogen fluoride.

Based on the overall process via stages 1) to 3), hydrogen fluoride is used, for example, in an amount of 4.5 to 8, preferably 4.8 to 7.5 and particularly preferably 4.8 to 6.0 mol of hydrogen fluoride per mole of phosphorus trichloride.

Typically, the gas containing phosphorus pentafluoride is therefore a gas mixture containing 5 to 41% by weight of phosphoφentafluoride, 6 to 59% by weight of hydrogen chloride and 0 to 50% by weight of hydrogen fluoride, preferably 20 to 41% by weight of phosphorus pentafluoride, 40 to 59 % By weight of hydrogen chloride and 0 to 40% by weight of hydrogen fluoride, particularly preferably 33 to 41% by weight of phosphorus pentafluoride, 49 to 59% by weight of hydrogen chloride and 0 to 18% by weight of hydrogen fluoride, the proportion of phosphorus pentafluoride, Hydrogen chloride and hydrogen fluoride, for example 11 to 100 wt .-%, preferably 90 to 100 wt .-% and particularly preferably 95 to 100 wt .-% is. The reaction pressure in step a) is, for example, 500 hPa to 5 MPa, preferably 900 hPa to 1 MPa, and more preferably 0, 1 MPa to 0.5 MPa.

The reaction temperature in step a) is for example -60 ° C to 150 ° C, preferably between 20 ° C to 150 ° C and most preferably between -10 ° C and 20 ° C or between 50 ° C and 120 ° C. At temperatures above 120 ° C., it is preferable to work under a pressure of at least 1500 hPa.

The reaction time in step a) is, for example, 10 s to 24 h, preferably 5 m to 10 h.

When using a gas containing phosphorus pentafluoride and hydrogen chloride gas leaving the fixed bed reactor or the fluidized bed in an aqueous solution of alkali hydroxide, preferably an aqueous solution of potassium hydroxide, more preferably in a 5 to 30 wt%, most preferably in a 10 to 20 wt .-%, in particular preferably in one 15 wt .-% potassium hydroxide collected in water. Surprisingly, under the conditions typical of the invention, hydrogen chloride does not react measurably with lithium fluoride, so that hydrogen chloride exits from the fixed-bed or fluidized-bed reactor and is then preferably neutralized. Preferably, the preparation of the gas or gas mixture used in step a) takes place in the gas phase. The reactors to be used for this purpose, preferably tube reactors, in particular stainless steel tubes, and the fixed bed or fluidized bed reactors to be used for the synthesis of the limium difluorophosphate are known to the person skilled in the art and are described, for example, in the Textbook of Technical Chemistry - Volume 1, Chemische Reaktionstechnik, M. Baerns, H. Hofmann, A. Renken, Georg Thieme Verlag Stuttgart (1987), pp. 249-256.

If solutions containing limium difluorophosphate are to be prepared, it is preferable to carry out the contacting of the reaction mixture formed according to a), which contains limium difluorophosphate, with an organic solvent in step b).

The reaction mixture typically contains the desired product lithium difluorophosphate and unreacted lithium fluoride.

Preferably, the reaction is conducted so that 1 to 98 wt .-%, preferably 2 to 80 wt .-% and particularly preferably 4 to 80 wt .-% of the solid lithium fluoride used are converted into lithium difluorophosphate.

The contacting of the reaction mixture formed according to a) with an organic solvent is carried out in a preferred embodiment after the fixed bed or the fluidized bed is purged with inert gas and thus traces of fluorine or hydrogen chloride or phosphorus pentafluoride have been removed. Inert gases are to be understood as meaning gases which do not react with phosphorus pentafluoride, fluorine or hydrogen chloride or lithium fluoride under the usual reaction conditions. Examples are nitrogen, argon and other noble gases or carbon dioxide, with nitrogen being preferred.

Organic solvents which are preferably used are organic solvents which are liquid at room temperature and have a boiling point of 300 ° C. or less at 1013 hPa and which furthermore contain at least one oxygen atom and / or one nitrogen atom.

Preferred solvents are furthermore those which have no protons which have a pKa value at 25 ° C., based on water or an aqueous comparison system of less than 20. Such solvents are also referred to in the literature as "aprotic" solvents. Examples of such solvents are liquid at room temperature nitriles, esters, ketones, ethers, acid amides or sulfones.

Examples of nitriles are acetonitrile, propanitrile and benzonitrile.

Examples of ethers are diethyl ether, diisopropyl ether, methyl tert-butyl ether, ethylene glycol dimethyl and diethyl ether, 1,3-propanediol dimethyl and diethyl ether, dioxane and tetrahydrofuran.

Examples of esters are methyl and ethyl acetate and butyl acetate or organic carbonates such as dimethyl carbonate (DMC), diethyl carbonate (DEC) or propylene carbonate (PC) or ethylene carbonate (EC). An example of sulfones is sulfolane.

Examples of ketones are acetone, methyl ethyl ketone and acetophenone

Examples of acid amides are N, N-dimethylformamide, Ν, Ν-dimethylacetamide, N-methylformanilide, N-methylpyrrolidone or hexamethylphosphoric triamide.

Particular preference is given to using acetonitrile, dimethyl carbonate (DMC), diethyl carbonate (DEC), propylene carbonate (PC) or ethylene carbonate (EC) or a mixture of two or more of these solvents. Particular preference is given to using dimethyl carbonate.

Preferably, contacting the reaction mixture formed with an organic solvent to dissolve the resulting Limiumdifluorphosphats for a period of 5 minutes to 24 hours, more preferably from 1 hour to 5 hours when using a bed or fluidized bed reactor such that the reactor contents of the fixed bed reactor or of the fluidized-bed reactor is brought into contact with organic solvent as long as possible, preferably with stirring or with pumping over, until the content of lithium difluorophosphate in the solvent remains constant.

For example, the weight ratio of organic solvent used to originally used lithium fluoride is 1: 5 to 100: 1.

In a further embodiment, the amount of organic solvent used is such that the concentration of limonium difluorophosphate in the organic solvent resulting from step b) or c) is from 0.1 to the solubility limit in the solvent used at the dissolution temperature, for example from 0.1 to 37% by weight. % preferably from 0.3 to 10% by weight and particularly preferably from 2 to 10 wt .-% is. For example, WO2012 / 004188 discloses to the person skilled in the art the different solubilities of limonium difluorophosphate in organic solvents.

The organic solvent to be used is preferably subjected to a drying process prior to its use, more preferably a drying process over a molecular sieve.

The water content of the organic solvent should be as low as possible. In one embodiment, it is from 0 to 500 ppm, preferably from 0 to 200 ppm and more preferably from 0 to 100 ppm. Molecular sieves which are preferably used for drying according to the invention are zeolites.

Zeolites are crystalline aluminosilicates that can be found in many modifications in nature, but can also be produced synthetically. More than 150 different zeolites have been synthesized, 48 naturally occurring zeolites are known. The natural zeolites are summarized mineralogically under the term zeolite group. The composition of the substance group zeolites is:

Mn ⁺ _{x / n} [A10 ₂ ] _x (Si0 ₂ ) _y ] z H ₂ 0

The factor n is the charge of the cation M and is preferably 1 or 2.

M is preferably a cation of an alkali or alkaline earth metal. These cations are required for electrical charge balance of the negatively charged aluminum Tertraeder and are not incorporated into the main Gitte of the crystal, but remain in cavities of the lattice and are therefore also easily within the grid movable and also in the

Retrospectively interchangeable.

The factor z indicates how many water molecules were absorbed by the crystal.

Zeolites can absorb water and other low-molecular substances and release them again on heating without destroying their crystal structure.

The molar ratio of Si0 ₂ to A10 ₂ or x / y in the empirical formula is referred to as modulus. It can not be less than 1 due to the Löwenstein rule.

Synthetic zeolites preferably to be used as molecular sieve according to the invention are: Zeolite composition of the unit cell

Zeolite A Na ₁₂ [(A10 ₂ ) ₁₂ (Si0 ₂ ) ₁₂ ] -27 H ₂ 0

Zeolite X Na ₈₆ [(AlO ₂ ) ₈₆ (SiO ₂ ) ₁₀₆ ] -264 H ₂ 0

Zeolite Y Na ₅ 6 [(AlO ₂ ) ₈₆ (SiO ₂ ) ₁₃ 6] -250 H ₂ 0

Zeolite LK ₉ [(A10 ₂ ) ₉ (Si0 ₂ ) ₂₇ ] -22 H ₂ 0

Mordenite Na _8J [(A10 ₂ ) ₈₆ (Si0 ₂ ) ₃₉ ] -24 H ₂ 0

ZSM 5 Nao, 3H3, ₈ [(A102) 4, l (Si0 ₂ ) 91.9]

ZSM 1 1 Na ₀ , iH ₁ , ₇ [(AlO 2) i, ₈ (SiO ₂ ) 94.2]

As a rule, the lithiumdifluorophosphate-containing organic solvent also contains proportions of unreacted, not or not appreciably soluble lithium fluoride, which is separated off from the organic solvent in accordance with step c). The separation in step c) preferably takes place by means of filtration, sedimentation, centrifugation or flotation, particularly preferably by means of filtration, particularly preferably by filtration through a filter having an average pore size of 200 nm or less. Further possibilities for solids separation are known to the person skilled in the art.

The separated lithium fluoride is preferably recycled for use in step a). In this way, a total of 60 wt .-% or more, preferably 70 wt .-% or more of the lithium fluoride used can ultimately be converted into Limiimidifluorphosphat.

The apparatus used in the present work is described in FIG. In Fig. 2 mean

1 template tempered, anhydrous hydrogen fluoride with Massflow controller

2 original phosphorus trichloride

3 template elemental chlorine

4 pump

5 phosphorus trichloride evaporator

6 stainless steel pipe

7 stainless steel pipe

8 heat exchangers

9 fluidized bed reactor 10 stirrers

11 scrubbers

12 disposal containers

Preferably, a combination of at least two series-connected tube reactors, preferably stainless steel tube 6 and stainless steel tube 7, is used for the production of phosphorus pentafluoride in combination via at least one heat exchanger with at least one fixed bed reactor or fluidized bed reactor, in which then the reaction of the phosphorus pentafluoride and finally hydrous, solid lithium fluoride to lithium difluorophosphate he follows.

The reaction flow of the reactants is described by way of example with reference to FIG. 2, here with two tubular reactors, a heat exchanger and a fluidized-bed reactor, as follows. By a heated stainless steel tube 6, preferably at temperatures of 20 ° C to 600 ° C, more preferably at 300 ° C to 500 ° C, pre-tempered hydrogen fluoride, preferably pre-heated to 30 ° C to 100 ° C, gaseously dosed from a template 1 and reacted with gaseous phosphorus trichloride. The gaseous phosphorus trichloride is previously liquid from template 2 by means of pump 4 in the evaporator 5, preferably tempered between 100 ° C and 400 ° C, more preferably between 200 ° C and 300 ° C, transferred and mixed from this with the hydrogen fluoride in stainless steel pipe 6 and this heated, preferably at the above temperatures. The resulting reaction mixture is transferred into stainless steel tube 7 and mixed there with elemental chlorine from the original 3, preferably heated to 20 ° C to 400 ° C, more preferably to 200 ° C to 300 ° C, and reacted. The resulting gas mixture containing phosphorus pentafluoride is cooled by means of heat exchangers, preferably at -60 ° C to 80 ° C, more preferably at -10 ° C to 20 ° C, and with solid lithium fluoride in the fluidized bed reactor 9, preferably at temperatures of -60 ° C. up to 150 ° C, preferably between 20 ° C to 150 ° C and most preferably between -10 ° C and 20 ° C or between 50 and 120 ° C, brought into contact, preferably by stirring by means of stirrer 10, or by turbulence or a combination of both. The gas mixture leaving the fluidized-bed reactor 9 is freed of acidic gases in the scrubber 11 and the resulting halide-containing solution is transferred to the disposal container 12. The solid reaction mixture remains in the fixed bed reactor / fluidized bed reactor 9 and is there partially dissolved by contacting with the organic solvent and the resulting suspension separated from the solid. Depending on the water content of the lithium fluoride used, it is also possible to controllably produce different amounts of lithium hexafluorophosphate in the reaction. In this respect, the method according to the invention is also suitable for selectively producing solutions of limonium difluorophosphate and lithium hexafluorophosphate in organic solvents. Unless a separation of Lithiumhexafluorophosphat of Limiumdifluorphosphat is desired, you can make the typically very different solubility in organic solvents to advantage and enforce in a subsequent step c2), for example, a solvent in which Limiumdifluorphosphat is less soluble than in the solvent used in step b) to thereby precipitate limium difluorophosphate. For example, in step b) acetonitrile, ketones such as acetone and ethers such as dimethoxyethane can be used and the precipitation can be carried out for example with diethyl carbonate, dimethyl carbonate or ethylene carbonate or propylene carbonate. Lithium hexafluorophosphate remains in solution. The amount required for the precipitation can be determined by the expert in a simple preliminary test. In this way, limonium difluorophosphate can be produced with as little foreign metal ion as is not obtainable according to the prior art processes.

Therefore, the invention also includes lithium difluorophosphate having a purity of 99.9000 to 99.9995 wt.%, Preferably 99.9500 to 99.9995 wt.% And particularly preferably 99.9700 to 99.9995 based on anhydrous product.

The lithium difluorophosphate further preferably has foreign ions

1) a content of 0, 1 to 75 ppm, preferably 0, 1 to 50 and particularly preferably 0.5 to 10 ppm and particularly preferably 0.5 to 5 ppm of sodium in ionic form and

2) a content of 0.01 to 10 ppm, preferably 0.5 to 5 ppm and more preferably 0.1 to 1 ppm of potassium in ionic form.

The lithium fluoride further preferably has foreign ions

3) a content of 0.05 to 300 ppm, preferably 0.1 to 250 ppm and more preferably 0.5 to 100 ppm of calcium in ionic form and / or

In one embodiment, the limonium difluorophosphate contains a total of foreign metal ion content of 300 ppm or less, preferably 20 ppm or less, and more preferably 10 ppm or less.

If the solution containing limonium difluorophosphate is not used directly as an electrolyte or for the preparation of an electrolyte, the removal of organic solvent can be carried out as step d) at least in part. If the removal is partial, the setting of a specific content of Lithiumdifluorphosphat is possible. If it is largely complete, it is also possible to obtain high-purity lithium difluorophosphate as a solid. Almost complete here means that the remaining content of organic solvent is 5000 ppm or less, preferably 2000 ppm or less.

The invention therefore furthermore relates to the use of the solutions obtained according to the invention as or for the preparation of electrolytes for lithium batteries or for the production of solid lithium difluorophosphate.

The invention further relates to a process for the preparation of electrolytes containing lithium difluorophosphate for lithium batteries characterized in that it comprises at least steps a) to c) and optionally d).

The advantage of the invention lies in particular in the efficient procedure and the high purity of the resulting Limiimidifluorphosphats.

Examples

In the following, the term "%" always means wt .-%.

With regard to the ion chromatography used in the present work, reference is made to the publication of the TU Bergakademie Freiberg, Faculty of Chemistry and Physics, Institute of Analytical Chemistry from March 2002 and the literature cited therein.

In the present work, the concentration of LiP0 ₂ F _{2 was} measured with an ion chromatograph with the following parameters:

Device type: Dionex ICS 2100

Column: IonPac® AS20 2 * 250-mm "Analytical Column with guard"

Sample volume: 1 μΐ

Eluent: KOH gradient: 0 min / 15 mM, 10 min / 15 mM, 13 min / 80 mM, 27 min / 100 mM, 27.1 min / 15 mM, 34 min / 15 mM

Eluent flow rate: 0.25 ml / min

Temperature: 30 ° C

Self-Regenerating Suppressor: ASRS® 300 (2-mm)

The assignment of the signals obtained to LiP02F2 was confirmed by 31P and 19F NMR spectroscopy. Details on the separation of LiP02F2 from other phosphorus fluorine-containing compounds by ion chromatography can also be found in Lydia Terborg Sascha Nowak, Stefano Passerini, Martin Winter, Uwe Karst, Paul R. Haddad, Pavel N. Nesterenko, Analytica Chimica Acta 714 (2012) 121 - 126.

Example 1: Preparation of high purity lithium fluoride

In a device according to FIG. 1, in the original 3, 500 g of solid lithium carbonate of industrial grade (purity:> 98% by weight, Na: 231 ppm, K: 98 ppm, Mg: 66 ppm, Ca: 239 ppm) and 20 liters of water submitted and prepared at 20 ° C, a suspension. After about five minutes, the suspension was passed through the filtration unit 6, which was designed as a cross-flow filter, and the resulting medium containing dissolved lithium carbonate, here an aqueous solution of lithium carbonate with a content of 1.32 wt .-%, via line 8th transferred to the reactor 9. After a total of 4 kg of the medium were pumped into the reactor 9, the feed from the filtration unit 6 and was stopped in the reactor 9 gaseous hydrogen fluoride in the gas space 1 1 with continuous pumping of the medium through the pump 13, the line 14 and the packed column 15th began. This dosage was terminated when the pH of the pumped solution was 7.0.

The resulting suspension from the reactor 9 was conveyed via the pump 17 and the line 18 to the filtration unit 19, which was designed here as Drucknutsche, filtered there, and the filtrate, here fed back a lithium carbonate-free aqueous medium via the line 20 to the template 3. The lithium carbonate-free aqueous medium had a content of lithium fluoride of about 0.05% by weight.

The above procedure was repeated five times.

The water-moist lithium fluoride separated off at the filtration unit 19 (total 148 g) was removed and washed on a further pressure filter with water having a conductivity of 5 Ωcm at 25 ° C. (30 ml each). The lithium fluoride thus obtained was dried in a vacuum oven at 90 ° C and 100mbar.

Yield: 120g of a white, fine powder.

The product obtained had a potassium content of 0.5 ppm and a sodium content of 2.5 ppm, the magnesium content of the product was 99 ppm, the calcium content of 256 ppm. The chloride content was less than 10 ppm.

The residual moisture content was 500 ppm water

The measurement of the particle size distribution gave a D50 value of 45 μπι and a D10 value of 22 μπι. The bulk density was 1.00 g / cm ³ .

When performing 50 cycles (repetitions), a total of 97% of the lithium carbonate used was obtained in the form of high-purity lithium fluoride. Example 2a Preparation of Highly Pure Lithium Difluorophosphate in Acetonitrile (Inventive)

Through a heated to 450 ° C, about 6 m long stainless steel tube (ID 8mm) was passed a mixture of 0.6 g / min PC1 ₃ and the slightly more than five times equimolar amount of HF (both in gaseous form). In this reaction mixture 8 1 / h of chlorine were introduced and passed through another, about 4 m long stainless steel tube (ID 8mm), which was heated to 250 ° C.

The reaction product was cooled to -20 and then passed through a fixed bed reactor approximately 45 mm in diameter which was partially filled with lithium fluoride according to Example 1 (69.5 g). 500μl of water was added to this powder using a syringe. The powder was stirred with a stirrer, also under reaction conditions. The total water content was 7140 ppm.

The gas mixture leaving this lithium fluoride-filled reactor was collected in an aqueous 15% by weight KOH.

After a total of about 7 hours of reaction time, the dosage of the educts was replaced by the metering of an inert gas and the reaction gas displaced from the system. Subsequently, the reaction product was washed in three portions with a total of 1000 ml of acetonitrile dried over molecular sieve 3A and the washing solutions were analyzed.

A total of 15.8 g of limium difluorophosphate was obtained in the form of a solution in acetonitrile. By extending the reaction time, lengthening the contact time and increasing the reaction temperature and increasing the water content, the yield and the ratio of limium difluorophosphate to limonium hexafluorophosphate can be further increased.

The solution further contained 21.52 g of lithium hexafluorophosphate.

Example 3: Attempting to Prepare Lithium Difluorophosphate in Acetonitrile (Not According to the Invention)

The procedure was completely analogous to Example 2 with the difference that no water was added to the lithium fluoride, ie the lithium fluoride had a water content of 500 ppm. Furthermore, the reaction time was extended to 13.5 hours. Overall, in addition to 80.5 g Lithiumhexafluorophosphat only 0.095 g of calcium in the form of a solution in acetonitrile, despite the longer reaction time and the higher reaction gas temperature.

Claims

A process for preparing limonium difluorophosphate comprising at least the step of: a) contacting solid lithium fluoride with a gas containing phosphorus pentafluoride, the solid lithium fluoride having a water content of more than 1500 ppm, preferably 1550 ppm or more, more preferably 1550 ppm to 100,000 ppm, even more preferred 2,000 ppm to 20,000 ppm and most preferably 5,000 ppm to 15,000 ppm.

A method according to claim 1, characterized in that solutions of Limiumdifluorphosphat are prepared in organic solvent and at least following steps follow: b) contacting the reaction mixture formed according to a) containing Limiumdifluorphosphat with an organic solvent, wherein the Limiimidifiuorphosphat formed is at least partially in solution

A method according to claim 1 or 2, characterized in that the lithium fluoride used in step a) has a purity of 98.0000 to 99.9999 wt .-%, preferably 99.0000 to 99.9999 wt .-%, more preferably 99, 9000 to 99.9995% by weight, particularly preferably 99.9500 to 99.9995% by weight and very particularly preferably 99.9700 to 99.9995% by weight, based on anhydrous product.

Process according to one of Claims 1 to 3, characterized in that the lithium fluoride used in step a) comprises foreign ions:

A content of 0.1 to 250 ppm, preferably 0, 1 to 75 ppm, more preferably 0 to 1 to 50 and particularly preferably 0.5 to 10 ppm and most preferably 0.5 to 5 ppm of sodium in ionic form and

A content of 0.01 to 200 ppm, preferably 0.01 to 10 ppm, more preferably 0.5 to 5 ppm and particularly preferably 0.1 to 1 ppm of potassium in ionic form.

Process according to one of Claims 1 to 4, characterized in that the lithium fluoride used in step a) comprises foreign ions: A content of 0.05 to 500 ppm, preferably 0.05 to 300 ppm, more preferably 0, 1 to 250 ppm and particularly preferably 0.5 to 100 ppm of calcium in ionic form and / or

A content of 0.05 to 300 ppm, preferably 0, 1 to 250 ppm and particularly preferably 0.5 to 50 ppm of magnesium in ionic form.

6. The method according to any one of claims 1 to 5, characterized in that the contacting of solid lithium fluoride containing the specified according to claim 1 water content is carried out with a gas containing phosphorus pentafluoride in a fixed bed or a fluidized bed.

7. The method according to any one of claims 1 to 5, characterized in that the lithium fluoride used is obtained by a process comprising at least the following steps: a) providing an aqueous medium containing dissolved lithium carbonate b) reacting the aqueous medium provided according to a) with gaseous

Hydrogen fluoride to an aqueous suspension of solid lithium fluoride. C) Separation of the solid lithium fluoride from the aqueous suspension

d) drying the separated lithium fluoride

8. The method according to any one of claims 1 to 7, characterized in that the phosphorus pentafluoride is prepared by a process comprising at least the following steps.

1) Reaction of phosphorus trichloride with hydrogen fluoride to phosphorus trifluoride and hydrogen chloride

3) Reaction of phosphorodichloride trifluoride with hydrogen fluoride to form phosphorus pentafluoride and hydrogen chloride or by reacting tetraphosphorodecoxide with hydrogen fluoride. Method according to one of claims 1 to 8, characterized in that the reaction pressure in step a) is 500 hPa to 5 MPa, preferably 900 hPa to 1 MPa and particularly preferably 1500 hPa to 0.5 MPa.

Method according to one of claims 2 to 9, characterized in that the organic solvent used are those which are liquid at room temperature and have a boiling point of 300 ° C or less at 1013 hPa and which further contain at least one oxygen atom and / or one nitrogen atom ,

11. The method according to claim 10, characterized in that are used as solvent at room temperature liquid nitriles, esters, ketones, ethers, acid amides or sulfones.

12. The method according to any one of claims 2 to 11, characterized in that to obtain solid Limiumdifluorphosphat either in a subsequent step c2) is added an organic solvent in which Limiumdifluorphosphat is less soluble than in the organic solvent in step b) was used to drop lithium difluorophosphate or in a step d) the organic solvent is removed.

13. Limonium difluorophosphate having a purity of 99.9000 to 99.9995% by weight, preferably 99.9500 to 99.9995% by weight, and particularly preferably 99.9700 to 99.9995, based on anhydrous product.

Lithium difluorophosphate according to claim 13 containing at foreign ions:

A content of 0, 1 to 75 ppm, preferably 0, 1 to 50 and particularly preferably 0.5 to 10 ppm and particularly preferably 0.5 to 5 ppm of sodium in ionic form and

a content of 0.01 to 10 ppm, preferably 0.5 to 5 ppm, and more preferably 0.1 to 1 ppm of potassium in ionic form, and preferably further a content of 0.05 to 300 ppm, preferably 0, 1 to 250 ppm and particularly preferably 0.5 to 100 ppm of calcium in ionic form and / or

a content of 0.05 to 300 ppm, preferably 0.1 to 250 ppm and more preferably 0.5 to 50 ppm of magnesium in ionic form wherein particularly preferably the Limiumdifluorphosphat has a content of foreign metal ions of a total of 300 ppm or less, preferably 20 ppm or less, and more preferably 10 ppm or less.

15. A process for the preparation of electrolytes containing calcium trifluorophosphate lithium batteries characterized in that it comprises at least steps a) to c) and optionally c2) and / or d).