WO1999041193A1

WO1999041193A1 - METHOD FOR PRODUCING PURE LiPF¿6?

Info

Publication number: WO1999041193A1
Application number: PCT/EP1999/000141
Authority: WO
Inventors: Klaus Schade; Ulrich Wietelmann
Original assignee: Metallgesellschaft Aktiengesellschaft
Priority date: 1998-02-12
Filing date: 1999-01-13
Publication date: 1999-08-19
Also published as: DE19805356C1

Abstract

The invention relates to a method for producing pure LiPF6 from LiF and PCl5 in diethyl ether. According to said method a suspension of LiF in diethyl ether is acidified with an anhydrous protic acid HX and then reacted with PCl5. After completion of the reaction the mixture is neutralised, filtered and either evaporated to dryness or LiPF6 is crystallized out by means of a cystallizing agent.

Description

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The invention relates to a process for the production of pure lithium hexafluorophosphate, LiPF _s , from LiF and PC1 _S in diethyl ether.

Lithium hexafluorophosphate, LiPF _s , is currently used as a conductive salt in all commercial lithium ion batteries. LiPF _β is a moderately hydrolysis-sensitive substance that is extremely hygroscopic and releases hydrogen fluoride (HF) in contact with moist air. HF has an extremely damaging effect on the cycle stability of lithium ion batteries, since it can detach metals from the cathodes consisting of transition metal oxides and thus cause the electrodes to decay.

The battery manufacturers therefore prefer the LiPF _s in a form which is as little sensitive to hydrolysis as possible, ie which has the smallest possible specific surface area. Farther the LiPF ₆ should be free-flowing so that it can be processed in automated systems. Finally, it should be ensured that the not inconsiderable heat of solution is released in a controlled manner in the production of electrolyte solutions.

All of these requirements are met by a coarse LiPF ₅ crystal or granulate with an even grain distribution. This product must be available in the purest form possible, because it is known that, in addition to the lowest possible HF contents, a low chloride content is also necessary, for example, in order to ensure good cycle stability with rechargeable batteries.

Lithium hexafluorophosphate is usually prepared from purified PF ₅ and lithium fluoride in a solvent (HF or organic solvents such as diethyl ether or acetonitrile). Since the PF _S gas is contaminated on the one hand with impurities from the synthesis (for example POF ₃ , HC1 and others) and on the other hand during the reaction with LiF in a liquid medium with traces of moisture with the release of HF, POF ₃ , Li [P0 ₂ F ₂ ] among other products, the raw product obtained generally has to be cleaned due to the high purity requirements of the battery industry.

For cleaning, the raw product can e.g. can be recrystallized from anhydrous HF. This method has the disadvantage that the last traces of acid and lithium fluoride can only be separated off with great difficulty. In addition, because of the corrosive and toxic properties of HF, it requires complex reaction technology.

Therefore, synthetic processes that avoid the use of HF are easier to implement on an industrial scale. So is described in US Patent a method for the preparation of LiPF proposed _s 3,607,020, is reacted at the LiF with PF ₅ in an inert organic solvent, with especially lower as the solvent, are saturated alkyl and lower alkyl esters of aliphatic saturated monocarboxylic acids. This process has the disadvantage that PF ₅ gas must be synthesized immediately before the process is carried out, since this raw material is not available on the market.

In JP 09245807 A and CA-A 2,193,119 methods are described for the preparation of LiPF _s in which LiF is reacted with expensive, not available in large quantities PF _S gas in a non-aqueous organic solvent. The production of crystalline, solvent-free LiPF ₅ is not intended using these processes.

Another process (EP 643 433 B1) is based on ammonium hexafluorophosphate, which is carried out with LiH in aprotic solvents according to the equation

Solvent NH ₄ PF _ε + LiH> LiPF _s + NH ₃ T + H ₂ T (1)

to LiPF _{6 is} implemented. This process has the disadvantage that NH ₄ PF ₆ and LiH are relatively expensive raw materials.

In a further process (US Pat. No. 5,378,445), starting from MPF ₆ (M = Na, K, NH ₄ , NR ₄ ), the lithium compound is produced according to the equation

Solvent / NH ₃ MPF ₆ + LiX> LiPF _s + X4- (2)

M = Na, K, NH ₄ NR ₄ X = halogen etc. prepared as a solution in organic solvents. The process has the disadvantages that the metal hexafluorophosphates (MPF ₆ ) are not available or are only available at high prices and the solutions are contaminated by the anion X (for example 0.1% KC1 or 3% KBr).

DE 196 32543 A describes, among other things, a process for the production of LiPF ₆ from the cheap raw materials LiF and PC1 ₅ under autogenous pressure or optionally in organic solvents, in particular in diethyl ether, according to the equation

6 LiF PCI-LiPF _c 5 LiCl

suggested.

This process has the disadvantage that finely powdered, chloride-containing end products are formed (for example 0.2% Cl ^~ content in the printing process). It was also found that during the direct synthesis in diethyl ether there is a discoloration of the initially colorless reaction mixture. The bluish-black impurities remain in the raw LiPF ₆ product after removal of the solvent and are extremely difficult to separate.

When LiPF _s crystallize from organic donor solvents such as diethyl ether or acetonitrile, complexes usually form between LiPF ₆ and solvency (LiPF _s • D _x ; D = donor solvency, x = 1 ... 4). The solvate complexes, most of which are in the form of well-formed crystals, disintegrate into a surface-rich, poor surface when they are dried at temperatures below the solvate decomposition point manageable powder.

For example, the decomposition of the well-defined acetonitrile complex LiPF ₆ ^• (CH ₃ CN) ₄ under reduced pressure at temperatures up to 30 ° C. provides a pure, but surface-active, and therefore difficult to handle solvent-free product (US Pat. No. 3,594,402).

When LiPF ₆ is crystallized from diethyl ether, a solvate complex is also obtained, the solvate decomposition point of which is approximately 40 ° C. (own experiments).

The production of a solvate-free LiPF ₆ from an ethereal solution has been known for a long time. Thus, according to US Pat. No. 3,607,020, LiPF _{6 is produced} from LiF and PF _S in ether at 0 to 50 ° C. and the LiPF ₆ crystals obtained are dried at 30 to 35 ° C. under reduced pressure (0.2 mm).

Similarly, according to DE 196 14503 AI, the drying of the LiPF _s , which is produced by reacting LiF with PF _S and dissolved in diethyl ether, at max. 40 ° C under vacuum. Temperatures of about 40 ° C are generally not exceeded because product decomposition according to the equation

ΔT LiPF,> LiF + PF ₅ t (4, '

is feared. For example, US Pat. No. 3,594,402 claims that the dissociation according to reaction (4) begins at approximately 20 ° C. and LiPF ₆ decomposes at 30 to 40 ° C.

The LiPF _s isolated from ethereal solutions at temperatures of <40 ° C contains depending on the Manufacturing conditions a certain amount of "crystal ether" (about 1 to 2 mol), which can be removed relatively quickly and completely during vacuum drying, but inevitably a dusty, surface-rich product is obtained.

The object of the invention is to avoid the disadvantages known from the prior art and to create a process which, starting from cheap raw materials, provides a technically simple, manageable process, an easy to handle, pure LiPF ₆ , which has a purity of> 99, Has 8%.

The object is achieved by the method specified in claim 1. Subclaims 2 to 16 disclose features that further develop the method according to the invention. When the method according to the invention is carried out according to subclaims 17 to 20, a pure LiPF _β obtained by total evaporation is obtained. Alternatively ^~ process features are specified in the dependent claims 21 to 34, which lead to a product obtained by crystallization of high purity LiPF. ₆

In the process according to the invention, a diethyl ether-containing LiF suspension is reacted with PC1 _S , the LiF suspension being slightly acidified before the PC1 _{5 is} metered in. It has surprisingly been found that acidification, for example with HCl gas, accelerates the LiPF _s formation reaction and, at the same time, suppresses side reactions. The phenomenon that the discoloration of the reaction mixture does not occur or is greatly delayed is also particularly striking.

Before starting the reaction with PC1 ₅ , the LiF suspension containing diethyl ether is acidified. It is also possible to acidify the diethyl ether before adding LiF and use it for slurrying the lithium fluoride.

Anhydrous protic acids HX are used for acidification, where X can be: a halogen, sulfate or a carboxylic acid residue. Preferred acids are those whose corresponding lithium salts are as poorly soluble as possible in ether or ether / hydrocarbon mixtures. HC1 and HF gas are particularly preferred, the former being particularly advantageous because of the simpler handling.

The acid concentration can be between 0.01 and 0.5 mmol / g suspension. The range between 0.02 and 0.2 mmol / g is particularly preferred.

The reaction temperature is 0 to 35 ° C, the preferred range being between 15 and 30 ° C.

The response time will include influenced by the reaction temperature and stirring intensity. In the preferred temperature range between 15 and 30 ° C, typically 2 to 8 hours are required for a practically quantitative conversion. Depending on the reaction conditions chosen (acid concentration, metering time, stirring intensity, stoichiometry and temperatures), the reaction mixture remains colorless during the entire reaction time, or it only becomes yellowish or slightly bluish towards the end.

The PC1 _{5 is} metered into the acidified, well-stirred LiF suspension at temperatures between 0 and 35 ° C. The amount of PCl ₅ metered in is chosen so that 6.06 to 12 mol LiF are present per mol PC1 ₅ . Because the theoretical

Stoichiometric ratio PC1 ₅ to LiF 1: 6, LiF is present in a defined excess. A ratio PC1 ₅ to LiF of 1: 6.3 to 1: 7.2 is preferred. In principle, higher LiF surpluses lead to a faster and more complete utilization of the PC1 _{S used} , but the economy of the process is adversely affected.

After the end of the reaction, the reaction mixture is neutralized with a base, the amount of base to be used at least corresponds to the amount of acid used. Ammonia, LiOH, Li ₂ CO ₃ , LiH or organolithium compounds such as methyl lithium or butyllithium can be used as bases. Preferred are methyl lithium, which is available on the market in the form of an ethereal solution, and lithium hydride, which does not leave any troublesome by-products in the neutralization.

Because of the insolubility of lithium hydride, it is used (based on the amount of acid used) up to a 10-fold, preferably 3 to 6-fold, molar excess. Excess lithium hydride together with the ether-insoluble lithium halides can be conveniently removed by filtration.

The concentration of the lithium fluoride presented as a suspension in diethyl ether is preferably 10 to 40%.

Either pure, dry diethyl ether or a mixture of diethyl ether and a solvent consisting of one or more hydrocarbons is used as the reaction medium. Suitable hydrocarbons are alkanes, such as, for example, preferably pentane, hexane, heptane or cyclohexane and aromatics, such as, for example, preferably toluene, xylene or ethylbenzene. The amount of the additional solvent optionally used can vary within wide limits and can be, for example, 0.3 to 3 parts by weight of the amount of LiF. A further dilution is possible, but makes no sense for technical and economic reasons. The solvent can either be introduced as a whole before the acidification and metering in of PC1 ₅ , or it can be added during the PC1 _S metering or the after-reaction phase. It improves the stirrability of the reaction suspension and makes it possible to replace part of the more expensive diethyl ether. Furthermore, it can be used as a crystallization aid in the crystallization cleaning step (see below) to be carried out optionally. The neutralized reaction mixture is then filtered, decanted or centrifuged to remove the insoluble by-products and the excess lithium fluoride. An ethereal LiPF ₆ crude product solution is obtained in this way. The raw solution is contaminated, among other things, with chlorine-containing compounds, especially PC1 ₃ .

In the production of LiPF _e according to a state-of-the-art process (see also Comparative Example 1), in which non-acidified diethyl ether is used, approx. 0.5 to 1.5 mol% PC1 ₃ (determined from the integration ratio PC1 ₃ : PF _S ^" in the ³¹ P-NMR spectrum) was observed as an impurity. It was surprisingly found that the acidification of the diethyl ether by the process according to the invention leads to a significant decrease in the PC1 ₃ impurity: it is only in the region of the ^31st P-NMR detection sensitivity (approx. 0.02%) or below.

Insoluble constituents (LiCl, LiF, LiH, LiOH) of the ethereal crude LiPF ₆ product solution are filtered off, and the slightly yellowish or colorless LiPF ₆ solution is either dried by evaporation or further purified by crystallization in the manner described below.

By total evaporation, a moderately clean LiPF ₆ quality (content approx. 99.8%) can be obtained from the filtrate. In order to achieve a product which is easy to handle, ie one with a low specific surface area, the diethyl ether and the solvent which may be present are distilled off at normal or only moderately reduced pressure (600 to 1000 mbar). After removal of the majority of ether, the bottom temperature is increased to 40 to 100 ° C., preferably 50 to 75 ° C., by external heating. The pressure can be removed simultaneously to remove the last diethyl ether or further solvent residues

(reasonably) be reduced (to 0.1 to 10 mbar, for example). Surprisingly, at the relatively high temperatures 10

no product decomposition according to reaction equation (4) was observed. On the other hand, the bottom temperatures are above the decomposition point of the LiPF ₆ etherate, which is why an ether-free, dust-free solid product forms directly. Depending on the drying conditions chosen, either a lumpy product or a granulate is obtained.

For higher purity requirements, a

Crystallization process can be selected. For this purpose, an aprotic crystallization aid is added to the ethereal crude product solution, which does not or only very poorly dissolves LiPF _s in pure form and has a higher boiling point than diethyl ether.

Alternatively, the crude product solution, which has been pre-evaporated to a LiPF ₆ concentration of 20 to 50%, preferably 30 to 45%, can be mixed with the crystallization aid in pure diethyl ether and then filtered.

This crystallization aid is e.g. another ether (methyl tert-butyl ether (MTBE), dibutyl ether, diisopropyl ether), an alkane (e.g. heptane, methylcyclohexane, octane) or an aromatic hydrocarbon (e.g. benzene, toluene, ethylbenzene) or a mixture of the substances mentioned. Heptane, methylcyclohexane, toluene and methyl tert are particularly preferred. Butyl ether.

The amount of the crystallization aid is 0.2 to 5 parts by weight of the amount of LiPF _{6 present} in diethyl ether solution. 0.3 to 1.5 parts by weight, based on the dissolved LiPF _ε , are particularly preferred. 11

The LiPF ₆ solution in the solvent mixture defined above is concentrated at normal or slightly reduced pressure. The jacket temperature of the still is initially 40 to 70 ° C. According to the different boiling points, practically pure diethyl ether initially distills, which continuously worsens the solvent capacity of the remaining solvent for the impurities and also LiPF ₆ . When an Et ₂ 0: LiPF ₆ ratio of approximately 1.2 to 2.3 is reached, the distillation is interrupted and the distillation residue is freed of any precipitated impurities by filtration.

The clear filtrate is then evaporated further down to a residual amount of ether of 0 to 30%. The bottom temperature rises to about 40 to 90 ° C. Lithium hexafluorophosphate separates out as a colorless, coarsely crystalline solid. The solid is freed from the mother liquor by filtration or centrifugation. This solid / liquid is preferably

Separation step carried out at temperatures> 40 ° C.

The crystals are washed with an aliphatic and / or aromatic hydrocarbon, preferably pentane, hexane or toluene, and then dried. Drying is preferably carried out at elevated temperatures (30 to 50 ° C.) under reduced pressure.

In this way, a solvent-free, coarsely crystalline product with a purity of> 99.9% is obtained.

The subject matter of the invention is explained in more detail below with reference to comparative and exemplary embodiments.

Examples 1 and 5 were carried out for comparison purposes according to the prior art, the remaining examples were carried out according to the inventive method. 12

Example 1: (Comparative example): reaction of LiF with PC1 _S in neutral diethyl ether at 25 ° C. (according to German patent application 196 32543)

170.0 g (8.3 mol, 38% excess) of dried lithium fluoride were suspended in 920 g of diethyl ether in a 2-1 double jacket vessel. At an internal temperature of 25 ° C., 207 g (1.0 mol) of PC1 _S from a metering bulb were added over the course of 18 minutes. The internal temperature was kept below 28 ° C. by counter-cooling. After 2 hours, the reaction mixture began to turn violet; after adding 32 g (1.23 mol) of LiF again, the reaction suspension discolored briefly, but the violet color was observed again after 15 minutes.

After a reaction time of 3.5 hours, 2.6 g of LiH were added to the reaction mixture, and the mixture was stirred for a further 1.5 hours. The suspension was filtered and the residue was washed with 3 portions of ether.

963 g of a blue-gray solution were obtained. The solution was concentrated in vacuo at 25 ° C. (weight 518 g) and a sample was hydrolyzed and analyzed by elemental analysis:

Li = 1.12%; P = 5.25%; F = 18.5%; Cl = 0.48%

The raw LiPF _s yield was therefore approx. 128 g (84%), the solution had a LiPF _s content of approx. 24.7%. PC1 ₃ (δ ³¹ P = -220 ppm) could be detected in the ³¹ P-NMR spectrum, - the molar ratio PC1 ₃ : LiPF ₆ was approx. 1.2: 100. 13

Example 2: Reaction of LiF with PC1 _S in acidic diethyl ether at 25 ° C

256.8 g (9.90 mol, 10% excess) of LiF in 1184 g of hydrochloric diethyl ether (H ⁺ = 0.08 mmol / g, total 95 mmol) were introduced into a 3-1 double-jacket reactor with a Teflon dispersing disc, reflux condenser and solids metering device ) submitted. At an internal temperature between 24 and 27 ° C, 312 g (1.50 mol) of PC1 _{5 were} metered in in portions within 1 hour.

After a total reaction time of 5 hours, the solution began to turn slightly yellowish. 3.15 g (0.40 mol) of lithium hydride were carefully added (initially strong gas evolution) and the mixture was then refluxed for about 20 minutes.

After filtration, 1288 g of a clear, almost colorless solution were obtained (Li = 0.65%, F = 11.4%, P = 3.1%), the content of LiPF _{6 was} approximately 15.2% (corresponding to one LiPF _s - crude product yield of approx. 86%). According to the ³¹ P NMR spectrum, the molar ratio PC1 ₃ : LiPF _{6 was} 0.02: 100.

Examples 1 and 2 show that much less undesirable PC1 _{3 is} formed by acidification and product discoloration can be largely avoided.

Example 3: Reaction of LiF with PC1 ₅ in 0.07 mmol H ⁺ / g Et ₂ 0 at 20 to 37 ° C

18.8 g of dried LiF (726 mmol, 10% excess) in 103 g of hydrochloric acid diethyl ether (0.07 mmol of H ⁺ / g) were placed in a 250 ml Schlenk flask with reflux condenser and 22.8 g (110 mmol) PC1 ₅ added. As a result of the heat of reaction released, the reaction mixture heated to boiling (36 ° C.) within 13 minutes. After 50 minutes the temperature dropped back below 35 ° C. After 80 minutes one 14

slight reddish discoloration noticed.

Example 4: Reaction of LiF with PC1 ₅ in 0.14 mmol H ⁺ / g Et ₂ 0 at 20 to 37 ° C

As in Example 3, 20.6 g of LiF (793 mmol, 10% excess) in 100 g of hydrochloric acid diethyl ether (0.14 mmol H ⁺ / g, total amount

14 mmol) and 25.0 g (120 mmol) of PC1 _{S were} added. The mixture heated to boiling within about 7 minutes. After about 1.5 hours there was a very weak yellowing, which did not increase in the following 1.5 hours. 0.2 g (25 mmol) of LiH were added and

Boiled under reflux for 15 minutes. After filtration, a practically colorless ethereal LiPF ₆ solution was obtained.

Examples 3 and 4 (different variants of the process according to the invention) show that the different discoloration behavior is dependent on the acid concentration. At an acid concentration of 0.14 mmol / g, a colorless product solution was obtained even at relatively high reaction temperatures.

Example 5: (comparative example): total evaporation to powder

(according to German patent application 196 32543)

380 g of the filtered solution from Example 1 (LiPF _s content approx. 15.2%, corresponding to 57.8 g content) were in a rotary evaporator (bath temperature 30 to 40 ° C) in a vacuum (last 1 mbar) to dryness and constant weight evaporated. 53 g (yield: 92%) of a yellowish, dust-fine powder were obtained. 15

Example 6: Total inspection for granules

88 kg of a LiPF ₆ solution prepared as in Example 2 were first concentrated to a concentration of 31% LiPF _s . This concentrated solution was evaporated to dryness in a heatable planetary mixer (jacket temperature 45 to 55 ° C.) first at normal pressure, then in vacuo (about 50 mbar) in about 5 hours. 14.2 kg of yellowish granules (grain size 1 to 3 mm) were obtained.

Yield: 88%, Cl content: 0.08%.

Examples 5 and 6 demonstrate that when the bottom temperature is increased above 40 ° C., granules can be obtained, while below 40 ° C. a yellowish, dust-fine powder is obtained, and that pure LiPF _{6 is} produced by the process according to the invention.

Example 7: Crystallization from Et ₂ 0 / hexane at RT

364 g of a 38% ethereal LiPF _s solution (prepared analogously to Example 2) were mixed with 450 g of hexane at about 15 ° C. with stirring in about 30 minutes. The LiPF _s etherate precipitated in the form of partially well-formed crystal needles was isolated in a glass frit and washed with a little pentane. The filter-moist product (278 g) was dried in vacuo (0.1 mbar) at room temperature. 122 g (88%) of pure LiPF _{s were obtained} in the form of a white, very finely crystalline powder (purity> 99.9%).

Example 8: Crystallization from Et ₂ 0 / toluene at 50 to 70 ° C

In a 500 ml Schlenk flask, 91.4 g of crude LiPF ₆ (Cl content 1.2%) were dissolved in 144 g of ether and with 95 g of toluene 16

added. The cloudy solution was stirred for 30 minutes and then filtered.

The clear, yellow filtrate was concentrated at a pressure of 700 mbar and an oil bath temperature of 70 ° C until the distillate temperature rose to about 55 ° C. Colorless, coarse crystals precipitated out. The residue (213 g) was filtered while warm, the crystals were washed with toluene and hexane and then dried in vacuo. 79.7 g (87%) of pure LiPF _{6 were} obtained (Cl content 50 ppm).

Examples 7 and 8 according to the invention demonstrate the different crystallization behavior of LiPF _s from diethyl ether / hydrocarbon mixtures below and above about 40 ° C.

Example 9: Crystallization from Et ₂ 0 / toluene at 40 to 75 ° C

197 g of crude LiPF ₅ (Cl content 0.06%) were dissolved in 460 g of ether and 195 g of toluene were added. The slightly cloudy solution was stirred at RT for 2 hours and then filtered. The clear solution was concentrated at normal pressure and a bath temperature of initially 40 ° C., then increasing to 75 ° C. After 474 g of distillate had been separated off, the LiPF _{6 which} precipitated out in the form of large, colorless crystals was filtered off, washed and dried. The yield was 194 g (98%), the chloride content was <20 ppm.

This example shows that a chloride-free LiPF ₆ can be obtained practically without losses from a relatively pure LiPF _s raw product quality. 17

Example 10: Crystallization from Et ₂ 0 / toluene at approx. 60 ° C without polishing filtration

178 g of a yellow 20.1% crude ethereal LiPF ₆ solution (containing 0.4% chloride) were mixed with 36 g of toluene at RT. A yellow, clear solution was formed. Ether was distilled off on a rotary evaporator at a bath temperature of initially 50 ° C., later 60 ° C. and slightly reduced pressure (first 1000, then 700 mbar). After approximately 110 ml of distillate (= 55% of the ether) had been separated off, a precipitate began to separate. A further 60 ml of ether were distilled off. The suspension was filtered and the solid filtered off was washed with a little toluene and hexane.

31.3 g (88%) of a dust-free, coarsely crystalline and pure white crystallizate were obtained. The chloride content was still <20 ppm.

In this example, a dilute LiPF _s solution was mixed with a hydrocarbon and evaporated until solvate-free, pure LiPF ₅ failed. In the present case, the ether was not removed completely, so that the impurities remained in the solution and polishing filtration was not necessary.

Example 11: Crystallization from Et ₂ 0 / methylcyclohexane at 70 ° C

86.0 g of crude LiPF _s (Cl content 0.5%) were dissolved in 201 g of diethyl ether and 88 g of methylcyclohexane were added. The slightly cloudy solution was filtered; the clear filtrate was concentrated at a bath temperature of 70 ° C and a pressure of 800 mbar. 190 g of distillate were separated off and the residue was filtered. In this way, 84 g (98%) of a coarse crystals with a chloride content of 70 ppm 18th

be preserved.

It is clear from this example that saturated hydrocarbons can be used instead of the aromatic toluene.

Claims

19Pat-pn r-nsprf-rhe:

1. Process for the preparation of pure LiPF ₆ from LiF and PC1 ₅ in diethyl ether, characterized in that a suspension of LiF, diethyl ether and an anhydrous protic acid HX, where X is a halogen, sulfate or carboxylic acid residue, is reacted with PC1 _S , that the acid HX is neutralized with a base after the reaction, that the neutralized mixture is filtered and that the pure LiPF _{6 is} isolated from the filtrate.

Process according to Claim 1, characterized in that the acid suspension of LiF in diethyl ether is produced either by adding LiF in acidified diethyl ether or by acidifying a suspension of LiF in diethyl ether.

3. The method according to claim 1 or 2, characterized in that gaseous HC1 or gaseous HF is used as the acid HX.

Method according to one or more of claims 1 to 3, characterized in that the acid concentration is 0.01 to 0.5 mmol / g suspension.

5. The method according to claim 4, characterized in that the acid concentration is 0.02 to 0.2 mmol / g suspension.

6. The method according to one or more of claims 1 to 5, characterized in that the reaction temperature 0 to 20th

Is 35 ° C.

7. The method according to claim 6, characterized in that the reaction temperature is 15 to 30 ° C.

8. The method according to one or more of claims 1 to 7, characterized in that the reaction time is 2 to 8 hours.

Method according to one or more of claims 1 to 8, characterized in that PC1 ₅ to LiF is used in a molar ratio of 1: 6.06 to 1:12.

10. The method according to claim 9, characterized in that PC1 ₅ to LiF is used in a molar ratio of 1: 6.3 to 1: 7.2.

11. The method according to one or more of claims 1 to 10, characterized in that the base used is NH ₃ , LiOH, Li ₂ C0 ₃ , LiH or an organolithium compound.

12. The method according to claim 11, characterized in that LiH or methyl lithium is used as the base.

13. The method according to claim 11 or 12, characterized in that the base LiH is added up to a 10-fold molar excess to the amount of acid used.

14. The method according to claim 13, characterized in that the base LiH is added in a 3 to 6-fold molar excess to the amount of acid used. 21

15. The method according to one or more of claims 1 to 14, characterized in that LiF is suspended in so much diethyl ether that a suspension with a LiF concentration of 10 to 40% is formed.

16. The method according to one or more of claims 1 to 15, characterized in that 0.3 to 3 parts by weight of an aliphatic and / or aromatic solvent per part by weight of LiF are added before or during the reaction.

17. The method according to one or more of claims 1 to 16, characterized in that after the reaction, the diethyl ether and the solvent are removed by distillation.

A method according to claim 17, characterized in that the bottom temperature at the distillative removal of diethyl ether and solvent is 40 to 100 ° C towards the end of the distillation process.

19. The method according to claim 18, characterized in that the bottom temperature is 50 to 75 ° C.

20. The method according to one or more of claims 17 to 19, characterized in that the distillative diethyl ether and solvent removal is started at 1000 to 600 mbar and the pressure after separation of the majority of the diethyl ether and the solvent is gradually reduced and that finally at full Vacuum is dried. 22

21. The method according to one or more of claims 1 to 15, characterized in that an aprotic crystallization aid, which has a higher boiling point than diethyl ether and hardly or does not dissolve LiPF _s in pure form, is added after the solution of LiPF _{s has been converted} into diethyl ether becomes.

22. The method according to one or more of claims 1 to 15, characterized in that the LiPF ₆ solution in diethyl ether is evaporated to a LiPF _s concentration of 20 to 50%, preferably 30 to 45% and then an aprotic crystallization aid, which in turn has a higher boiling point than diethyl ether and in its pure form hardly or does not dissolve LiPF ₆ , is added. -

23. The method according to claim 21 and / or 22, characterized in that the crystallization aid is an alkane or an aromatic or an ether, preferably heptane or methylcyclohexane or toluene or methyl tert. - Butyl ether, is.

24. The method according to one or more of claims 21 to 23, characterized in that the

Crystallization aid in an amount of 0.2 to 5 parts by weight based on the amount of LiPF _{6 of} the solution is added.

25. The method according to claim 24, characterized in that the crystallization aid is added in an amount of 0.3 to 1.5 parts by weight, based on the amount of LiPF _{6 in} the solution. 23

26. The method according to one or more of claims 21 to

25, characterized in that the diethyl ether is distilled off to an Et ₂ 0: LiPF _s weight ratio of 1.2: 1 to 2.3: 1 and the solution is filtered.

27. The method according to one or more of claims 21 to

26, characterized in that the LiPF _s -containing solution is evaporated, the diethyl ether being distilled off to a residual amount of 0 to 30% of the amount initially introduced, the bottom temperature rising to 40 to 90 ° C and LiPF ₆ separates as a crystalline, solvate-free solid.

28. The method according to claim 27, characterized in that the deposited, crystalline LiPF _{s is} separated by filtration or centrifugation from the mother liquor.

29. The method according to claim 28, characterized in that the separation from the mother liquor is carried out at temperatures of over 40 ° C.

30. The method according to claim 28 or 29, characterized in that the crystalline LiPF _s with an aliphatic and / or aromatic hydrocarbon, preferably pentane or hexane or toluene, washed and then dried.

31. The method according to claim 30, characterized in that the crystalline LiPF ₆ washed with pentane or hexane or toluene and then dried.

32. The method according to claim 30 or 31, characterized in that the drying is carried out at temperatures of 20 to 70 ° C. 24

33. The method according to claim 32, characterized in that the drying is carried out at temperatures of 30 to 50 ° C.

34. The method according to claim 32 or 32, characterized in that the drying is carried out at reduced pressure.