The present invention claims benefit of the priorities of European patent application N° 10171881.5 filed August 4, 2010, and of European patent application N° 10188108.4 filed on October 19, 2010 the whole content of which is incorporated herein for all purposes. The present invention relates to a method for the manufacture of L1PO ₂ F ₂ ; more specifically, it relates to a method for the manufacture of L1PO ₂ F ₂ comprising a step of reacting a compound which has a P-F bond and is selected from the group consisting of phosphorus

pentafluoride (PF ₅ ), phosphoryl fluoride (POF ₃ ), and mixtures thereof, and lithium orthophosphate (L1 ₃ PO ₄ ). The present invention is also directed to the use of POF ₃ in the manufacture of L1PO ₂ F ₂ .

Lithium difluorophosphate, L1PO ₂ F ₂ , is useful as electrolyte salt or additive for an electrolyte composition comprising an electrolyte salt for lithium ion batteries. Thus, WO 2008/111367 discloses how to manufacture a mixture of LiPF ₆ and L1PO ₂ F ₂ from a halide other than a fluoride, LiPF ₆ and water. The resulting salt mixture, dissolved in aprotic solvents, is used as an electrolyte solution for lithium ion batteries. EP-A-2 061 115 describes, as state of the art at that time, the manufacture of L1PO ₂ F ₂ from P ₂ O ₃ F ₄ and Li compounds, and, as invention, the manufacture of L1PO ₂ F ₂ from LiPF ₆ and compounds with a Si-O-Si bond, e.g. siloxanes. US 2008-305402 and US 2008/102376 disclose the manufacture of L1PO ₂ F ₂ from LiPF ₆ with a carbonate compound ; according to US 2008/102376, LiPF ₆ decomposes at 50°C and above under formation of PF ₅ ; according to other publications, PF ₅ is only formed at and above the melting point of LiPF ₆ (~ 190°C). EP-A-2 065 339 discloses how to manufacture a mixture of LiPF ₆ and L1PO ₂ F ₂ from a halide other than a fluoride, LiPF ₆ and water. The resulting salt mixture, dissolved in aprotic solvents, is used as an electrolyte solution for lithium ion batteries.

However, the above methods are technically difficult and produce a greater amount of a by-product such as LiF which is not industrially interesting and thus would incur additional cost for the waste treatment. Further the starting material, LiPF ₆ , is expensive and thus its use increases the production cost. Consequently, there has been a need to develop new processes, which are capable of avoiding the drawbacks indicated above. Object of the present invention is to provide L1PO ₂ F ₂ in a technically feasible and economical manner. This object and other objects are achieved by the invention as outlined in the patent claims.

According to one aspect of the present invention, L1PO ₂ F ₂ is manufactured by the reaction of L1 ₃ PO ₄ and a compound having a P-F bond which compound is selected from the group consisting of POF ₃ , PF ₅ , and mixtures thereof. The resulting reaction mixture thereby obtained comprises L1PO ₂ F ₂ .

According to one embodiment, L1PO ₂ F ₂ is manufactured from PF ₅ and L1 ₃ PO ₄ . Both are cheap starting materials. Depending on the molar ratio of PF ₅ and L1 ₃ PO ₄ , the reaction mixture may comprise LiF and/or LiPF ₆ according to the reaction equations

PF ₅ + L1 ₃ PO ₄ 2 LiP0 ₂ F ₂ + LiF (I)

2 PF5 + U3PO4 2 LiP0 ₂ F ₂ + LiPF ₆ (II)

Especially the reaction according to equation (II) is advantageous because the LiPF ₆ produced is a valuable product per se.

According to another embodiment of the present invention, L1PO ₂ F ₂ is manufactured by the reaction of phosphoryl fluoride (POF ₃ ) and lithium orthophosphate (L13PO4).

2POF ₃ + Li ₃ P0 ₄ ^ 3 LiP0 ₂ F ₂ (III)

Since no by-product is ideally produced from this reaction, the purity of L1PO ₂ F ₂ is very high even without purification when compared to the process of the prior art where the reaction mixture contains at least one byproduct such as LiF.

Phosphoryl fluoride (POF ₃ ) can be obtained commercially, e.g. from ABCR GmbH & Co. KG, or can be prepared by a known process in the art. For example, POF ₃ can be prepared by fluorination of phosphoryl chloride with HF and/or other fluorinating agents, for example, ZnF ₂ . Alternatively, it may be also prepared by the reaction of H3PO4/P2O5, HF/H ₂ 0 and SO3/H2SO4. Sometimes, the POF ₃ obtained may contain PF ₅ as impurity, or vice versa, PF ₅ may comprise POF ₃ as impurity. The advantage of the process of the invention is that even such mixtures can be applied without impact on the yield.

PF ₅ may be obtained commercially, e.g. from Praxair, or it may be prepared from PCI ₅ and HF or, as described in EP-A-0 0816287, for example from PCI3, Cl ₂ and HF. L1 ₃ PO ₄ 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.

Consequently, the reactions of the invention are gas-solid reactions or, if a solvent for POF ₃ or PF ₅ , respectively, is applied, a gas-liquid-solid reaction or a liquid-solid reaction.

Preferably, the reaction between PF ₅ and L1 ₃ PO ₄ , between POF ₃ and L1 ₃ PO ₄ and between mixtures of POF ₃ and PF ₅ , respectively, and L1 ₃ PO ₄ is performed in the absence of water or moisture. Thus, the reaction may be performed at least for a part of its duration in the presence of an inert gas ; dry nitrogen is very suitable, but other dry inert gases may be applied, too. The reaction can be performed in an autoclave-type vessel or in other reactors. 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.

L1 ₃ PO ₄ 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 with POF ₃ , PF ₅ and mixtures therof.

The reactants POF ₃ or PF ₅ , respectively, can be introduced into the reaction in gaseous form or in the form of a solution in suitable aprotic organic solvents. Suitable solvents are, for example, ether compounds, e.g. diethyl ether, and organic solvents which are useful as solvents in lithium ion batteries ; many examples of such solvents, for example, especially organic carbonates, but also lactones, formamides, pyrrolidinones, oxazolidinones, nitroalkanes,

Ν,Ν-substituted urethanes, sulfolane, dialkyl sulfoxides, dialkyl sulfites, acetates, nitriles, acetamides, glycol ethers, dioxolanes, dialkyloxyethanes,

trifluoroacetamides, are given below.

In other embodiments, POF ₃ is introduced into the reactor in complex form, especially in the form of a donor-acceptor complex such as POF ₃ -amine complexes. Those complexes include POF ₃ - pyridine, POF ₃ -trietylamine, POF ₃ -tributylamine, POF ₃ -DMAP(4-(dimethylamino) pyridine),

POF ₃ -DBN(l,5-diazabicyclo[4.3.0]non-5-ene), POF ₃ -DBU(l,8- diazabicyclo[5.4.0]undec-7-ene), and POF ₃ -methylimidazole. In specific embodiments, a separate vessel can be used to supply POF ₃ to the reactor vessel. PF ₅ , too, can be introduced in such manner into the reactor.

POF ₃ , PF ₅ and any mixtures therof are preferably introduced into the reactor in gaseous form or in the form of a solution in an aprotic organic solvent. POF ₃ , PF ₅ and any mixtures therof are more preferably introduced into the reactor in gaseous form.

Preferably, no FIF is added to the reaction mixture. Preferably, no difluorophosphonc acid is added to the reaction mixture. Preferably, equal to or more than 80 %, more preferably, equal to or more than 85 %, and most preferably, 100 % of the P content in L1PO ₂ F ₂ produced originate from PF ₅ or POF ₃ and L1 ₃ PO ₄ introduced into the reaction according to equations (I), (II) and (III), and less than 20 % and preferably less than 5 % of the P content in L1PO2F2 produced originates from added LiPF ₆ ; most preferably, no LiPF ₆ is added at all.

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 POF ₃ , PF ₅ and any mixtures therof with L1 ₃ PO ₄ . For the reaction between POF ₃ and L1 ₃ PO ₄ , a preferred reaction time of 0.5 to 2 hours, most preferably of around 1 hour gives good results. For the reaction

between PF ₅ or mixtures of PF ₅ and POF ₃ and L1 ₃ PO ₄ , a preferred reaction time of 0.5 to 2 hours, most preferably of around 1 hour gives good results, too. The reaction speed is very fast.

The reaction temperature is preferably equal to or higher than 0°C.

Preferably, the reaction temperature is equal to or lower than 100°C.

The reaction temperature when reacting PF ₅ and L1 ₃ PO ₄ is preferably equal to or lower than 70°C, more preferably, it is equal to or lower than 50°C. Still more preferably, it is lower than 50°C, a especially preferably, it is lower than 45°C. Advantageously, the reaction of PF ₅ with L1 ₃ PO ₄ is performed at a temperature from 15 to 35°C, preferably at a temperature from 20 to 30°C, and most preferably, at ambient temperature.

When POF ₃ and L1 ₃ PO ₄ are reacted, the reaction temperature is preferably equal to or higher than ambient temperature (25°C), more preferably, equal to or higher than 50°C. The reaction temperature is preferably equal to or lower than 100°C, more preferably equal to or lower than 90°C. A preferred range of temperature is from 50 to 90° C.

If desired a reactor can be applied with internal heating or cooling means, or external heating or cooling means. It may have, for example, lines or pipes with a heat transfer agent like water.

The reaction between POF ₃ , PF ₅ or their mixtures with L1 ₃ PO ₄ may be performed at ambient pressure (1 bar abs.). Preferably, the reaction of POF ₃ , PF ₅ or their mixtures with L1 ₃ PO ₄ is performed at a pressure higher than 1 bar (abs.), more preferably at a pressure higher than 3 bar (abs.), most preferably, higher than 5 bar (abs). As the reaction proceeds, POF ₃ and PF ₅ , respectively, are consumed, and the pressure may consequently be decreasing, in an autoclave for example. The upper limit of the pressure during the reaction is not critical. Often, for practical reasons, the pressure is equal to or lower than 30 bar (abs).

The reaction of POF ₃ and PF ₅ or their mixtures with L1 ₃ PO ₄ can be performed batch wise, for example, in an autoclave. The reactor may have internal means, e.g. a stirrer, to provide a mechanical impakt on the surface of the solid particles of L1 ₃ PO ₄ to remove reaction product from t he surface and provide an unreacted fresh surface. It is also possible to shake or rotate the reactor itself.

Alternatively, the reaction can be performed continuously, for example, in a flow reactor. For example, the L1 ₃ PO ₄ may be provided in the form of a bed ; POF ₃ , PF ₅ or their mixtures may be passed through this bed until a

"breakthrough" of POF ₃ or PF ₅ is observed indicating the end of the reaction. If desired, dry inert gas like nitrogen or noble gases may be passed through the L1 ₃ PO ₄ bed to remove oxygen, moisture or both before performing the reaction.

If the reaction is performed continuously, for example, L1 ₃ PO ₄ may be kept in the form of a bed in a flow reactor, e.g. as a fluidized bed, and POF ₃ or PF ₅ or their mixtures is continuously passed through the bed. Continuously, POF ₃ and/or PF ₅ and unreacted L1 ₃ PO ₄ may be introduced into the reactor, and continuously, reaction product may be withdrawn from the reactor. Means, for example, moving parts, e.g. stirrers, may be foreseen in the reactor which provide a mechanical impact on the surface of the solid particles to remove reaction product from their surface and to provide unreacted L1 ₃ PO ₄ .

If desired, the reaction may be performed in a solvent, e.g. an organic polar aprotic solvent. Preferably, the L1 ₃ PO ₄ is dispersed therein. While it is not expected that a significant amount of L1 ₃ PO ₄ will dissolve in such a solvent, at least the solvent may serve to dissolve reaction products like LiF or LiPF ₆ thus making the isolation of L1PO ₂ F ₂ easier. If desired, the POF ₃ and PF ₅ or their mixtures, respectively, may be introduced into the reaction dissolved in an aprotic polar solvent, for example, in an ether, e.g. in a dialkyl ether, for example, in diethyl ether, or in other solvents, and especially in one of the solvents for lithium ion batteries mentioned below. Since LiPF ₆ is much better soluble in these solvents than L1PO ₂ F ₂ , the reaction between POF ₃ or PF ₅ and L1 ₃ PO ₄ and the subsequent removal of formed LiPF ₆ can be performed in the same reactor in a kind of "1 -pot process". This is especially preferred if a reaction between POF ₃ and L1 ₃ PO ₄ is performed because ideally, no by-product is formed, and also for the reaction between PF ₅ and L1 ₃ PO ₄ because the reaction can be performed such (by providing a relatively high molar ratio of PF ₅ :Li ₃ P0 ₄ , e.g. from 2 to 4) that the formation of LiF as by-product is suppressed and the formation of LiPF ₆ as by-product is increased ; this is explained below.

If desired, after termination of the reaction, a vacuum may be applied, or dry inert gas like nitrogen or noble gases may be passed through the L1PO ₂ F ₂ bed, to remove solvents or residual POF ₃ or PF ₅ .

The resulting reaction mixture is present in solid form if no solvent is used. If desired, the solid may be comminuted, e.g. milled, to provide a larger contact surface if it is intended to dissolve constituents of it.

If desired, the L1PO ₂ F ₂ formed can be isolated from the resulting reaction mixture which may comprise LiF and/or LiPF ₆ .

In the following, the reaction of PF ₅ and L1 ₃ PO ₄ is explained in more detail.

The molar ratio of PF ₅ to L1 ₃ PO ₄ is preferably equal to or greater than 0.9: 1. It is more preferably equal to or greater than 1 : 1.

Depending on the molar ratio of PF ₅ and L1 ₃ PO ₄ , the reaction with L1 ₃ PO ₄ can be influenced in view of the formation of LiF or LiPF ₆ as preferred side product.

According to one embodiment, the molar ratio of PF ₅ to L1 ₃ PO ₄ is equal to or lower than 2: 1, more preferably, lower than 2: 1. If the molar ratio of PF ₅ and L1 ₃ PO ₄ is between 0.9: 1, preferably 1 : 1, and 2: 1, it is expected that LiF and LiPF ₆ are formed and are present in the reaction mixture. The closer the ratio of PF ₅ and L1 ₃ PO ₄ is to 2: 1, the more LiPF ₆ is expected to be formed. The presence of LiPF ₆ as reaction product has the advantage that it can be separated from L1PO ₂ F ₂ very easily as is shown below because its solubility is much higher than that of L1PO ₂ F ₂ in a lot of organic solvents. The disadvantage is that LiPF ₆ is much more sensitive to moisture than LiF. To separate L1PO ₂ F ₂ from LiF, it is preferred to apply a solvent for L1PO ₂ F ₂ as explained below. It is possible and in some embodiments it is preferred that the resulting reaction mixture is heated to decompose LiPF ₆ to form LiF and PF ₅ . For example, if both LiF and LiPF ₆ are present as impurities, LiF is provided as single impurity thus making work-up easier.

According to another embodiment, the molar ratio of PF ₅ to L1 ₃ PO ₄ is equal to or greater than 2: 1. It is preferably equal to or lower than 4, more preferably, it is lower than 4, still more preferably, it is equal to or lower than 3. In this embodiment, L1PO ₂ F ₂ is formed containing LiPF ₆ as by-product. As mentioned above, LiPF ₆ can be removed easily from L1PO ₂ F ₂ by extraction with a solvent.

The molar ratio of POF ₃ to L1 ₃ PO ₄ is generally equal to or greater than 1.8: 1. It is more preferably equal to or greater than 2: 1. It is preferably equal to or lower than 5 : 1. According to one embodiment, the molar ratio of POF ₃ to L1 ₃ PO ₄ is equal to or lower than 4: 1. Preferably, the molar ratio of POF ₃ to L1 ₃ PO ₄ is equal to or greater than 2 and equal to or lower than 4.

If desired, mixtures comprising L1 ₃ PO ₂ F ₂ and LiPF ₆ in any desired ratio can be produced. In this case, L1 ₃ PO ₄ and LiF and sufficient PF ₅ are introduced into the reaction. PF ₅ forms LiPF ₆ with the introduced LiF, and it forms L1PO ₂ F ₂ (and some LiPF ₆ ) with the L1 ₃ PO ₄ introduced into the reaction.

To summarize,

a) the reaction of L1 ₃ PO ₄ with PF ₅ according to reraction scheme (I) provides a reaction product which essentially consists of L1PO ₂ F ₂ and LiF

b) the reaction of L1 ₃ PO ₄ with PF ₅ according to reraction scheme (II) provides a reaction product which essentially consists of L1PO ₂ F ₂ and LiPF ₆

c) the reaction of L1 ₃ PO ₄ with POF ₃ according to reraction scheme (III) provides a reaction product which essentially consists of L1PO ₂ F ₂ with at most minor amounts of impurities, e.g .LiF.

d) the reaction of a starting material comprising L1 ₃ PO ₄ and LiF with PF ₅ provides mixtures of L1PO ₂ F ₂ and LiPF ₆ in any desired ratio.

Main by-products according to a) and b) are LiF and LiPF ₆ , respectively ; only one of LiF and LiPF ₆ , or both, may be present. As outlined above, it is possible by properly selecting reaction conditions, especially the molar ratio of starting compounds (molar ratio of POF ₃ and PF ₅ , respectively, to L1 ₃ PO ₄ ) to influence the presence of LiF and LiPF ₆ as by-products. In some embodiments, the presence of LiF or LiPF ₆ may be desired. In such an embodiment, no further purification may be necessary. In other embodiments, it may be desired to obtain purified L1PO ₂ F ₂ , which is free of LiF or LiPF ₆ . If desired, the reaction mixture can be treated to obtain purified L1PO ₂ F ₂ ; to obtain purified L1PO ₂ F ₂ , two embodiments are preferred.

According to one embodiment, L1PO ₂ F ₂ can be purified including a step of extracting the reaction product with a solvent. L1PO ₂ F ₂ can be isolated by using a solvent or a solvent mixture which preferably dissolves L1PO ₂ F ₂ . This is the preferred way to separate L1PO ₂ F ₂ from mixtures which contain L1PO ₂ F ₂ and LiF as impurity, e.g. when obtained in a reaction mentioned above under a) and c). The dissolved L1PO ₂ F ₂ can be recovered from the solvent by removing it, e.g. by evaporation of the solvent. Optionally, a solution of L1PO ₂ F ₂ in a suitable solvent may directly be applied for the manufacture of an electrolyte for Li ion batteries.

According to another embodiment, L1PO ₂ F ₂ is purified from impurities by applying a solvent or solvent mixture which preferentially dissolves the impurity. This is the preferred way to separate L1PO ₂ F ₂ and LiPF ₆ , e.g. when a reaction mixture comprising both is obtained in a reaction mentioned above under b). In a preferred embodiment, formed LiPF ₆ is extracted with a solvent applicable in lithium ion batteries. In the following, certain solvents will be described which are preferably applied to separate L1PO ₂ F ₂ and LiF by preferentially dissolving LiP0 ₂ F ₂ .

If the reaction mixture comprises essentially only L1PO ₂ F ₂ and LiF, the separation is best achieved by contacting the reaction mixture with solvents which preferentially dissolve L1PO ₂ F ₂ . Aprotic and protic organic and inorganic solvents are suitable, especially polar solvents. The preferred inorganic solvent is water. Organic protic or aprotic solvents can be used for the extraction, too.

Suitable protic organic solvents are alcohols. Alcohols with one, two or three hydroxy groups in the molecule are preferred. Methanol, ethanol, n-propanol, i-propanol, glycol and glycerine are preferred alcohols. Glycol alkyl ethers, e.g. diglycol methyl ether, are also suitable. Also acetone, in its tautomeric form, can be considered as protic solvent.

Aprotic polar solvents are also very suitable for the extraction of L1PO ₂ F ₂ from the reaction mixture. Preferably, the aprotic organic solvent is selected from 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, wherein the alkylene group preferably comprises a bridge of 2 carbon atoms between the oxygen atoms of the -0-C(0)-0- group ; ketones, nitriles and formamides. Dimethyl formamide, carboxylic acid amides, for example, Ν,Ν-dimethyl acetamide and Ν,Ν-diethyl acetamide, 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, are suitable solvents.

It is also possible to use mixtures containing water and one or more organic protic or aprotic solvents. It is preferred that the pH of the water used for extraction, and of water-containing organic solvents applied for extraction, of the L1PO ₂ F ₂ formed in the reaction is selected such that undesired hydrolysis of L1PO ₂ F ₂ is prevented. Especially, the pH is equal to or lower than 7 to prevent hydrolysis. It is preferred to keep the pH at a value of equal to or lower than 7 during the contact of L1PO ₂ F ₂ with the water or the mixture of water and organic solvent or solvents.

Mixtures of water and protic solvents can be applied for the isolation of L1PO ₂ F ₂ , for example, mixtures of water and alcohols with 1, 2 or 3 hydroxy groups, e.g., mixtures of water and methanol, ethanol, isopropanol, n-propanol, glycol, glycerine or di glycol.

Mixtures of water and aprotic organic solvents, especially, polar aprotic solvents, can also be applied, for example, mixtures of water with one of the solvents mentioned above, e.g. with ethylene carbonate or propylene carbonate.

Of course, it also possible to apply mixtures which comprise water, one or more protic organic solvents and one or more aprotic organic solvents. For example, mixtures containing water, an alcohol like methanol, ethanol or i-propanol, and a nitrile, for example, acetonitrile, or propylene carbonate, can be applied. The content of water in these mixtures is preferably between 1 and 99 % by weight.

Aqueous or protic solvents may for example be applied when L1PO ₂ F ₂ is prepared from PF ₅ and L1 ₃ PO ₄ .

Dimethyl carbonate and propylene carbonate are among the preferred solvents for reaction mixtures which essentially consist of L1PO ₂ F ₂ and LiF because L1PO ₂ F ₂ is at least fairly soluble in these solvents while LiF is essentially insoluble. Other very suitable solvents to extract L1PO ₂ F ₂ from reaction mixtures comprising LiF obtained by the reaction of POF ₃ , PF ₅ or their mixtures with L1 ₃ PO ₄ as main impurity are ethylene carbonate (EC), ethyl methyl carbonate (EMC), ethyl acetate, diethyl carbonate, a mixture of dimethyl carbonate and propylene carbonate (PC), acetonitrile, dimethoxyethane and acetone. The solubility of L1PO ₂ F ₂ in these solvents at ambient temperature is compiled in the following table 1.

Table 1 : Solubility of L1PO ₂ F ₂ in certain solvents

The solubility of L1PO ₂ F ₂ in acetonitrile and especially in dimethoxyethane and acetone is remarkably high. Acetone is not very well suited as a solvent for Li ion batteries, but it may advantageously be used for the purification of L1PO ₂ F ₂ because it has a very high solubility for L1PO ₂ F ₂ and a very low solubility for LiF. Thus, mixtures comprising LiF and L1PO ₂ F ₂ can easily be separated by dissolving the L1PO ₂ F ₂ in acetone and filtration to remove solid LiFLiP0 ₂ F ₂ can be recovered from its solutions in acetone, for example, by evaporation of the acetone.

The solubility of L1PO ₂ F ₂ in dimethoxyethane is even higher than in acetone. Dimethoxyethane was considered as solvent or solvent additive for Li ion batteries. Thus, dimethoxyethane - which also dissolves LiF at most in neglectable amounts - can be used for the purification of L1PO ₂ F ₂ as described above in view of the use of acetone, and it can even be applied to raise the solubility of L1PO ₂ F ₂ in Li ion battery solvents.

Solutions of L1PO ₂ F ₂ in dimethyl carbonate, propylene carbonate and mixtures therof - which dissolve LiF at most in neglectable amounts - are especially suitable for the manufacture of battery electrolytes.

For the isolation of L1PO ₂ F ₂ from LiF or LiPF ₆ , and especially, if the reaction mixture contains L1PO ₂ F ₂ and LiPF ₆ as main impurity, water-free solvents are preferably applied.

This preferred embodiment - the use of essentially waterfree solvents for working up the reaction mixture obtained in the reaction between L1 ₃ PO ₄ and POF ₃ , PF ₅ or their mixtures - will be described now in detail.

If the reaction mixture contains essentially only L1PO ₂ F ₂ and LiF, it is preferred to apply solvents which preferentially dissolve L1PO ₂ F ₂ .

If the reaction mixture contains essentially only L1PO ₂ F ₂ and LiPF ₆ , it is preferred to apply solvents which preferentially dissolve LiPF ₆ . It was surprisingly found that certain solvents can be applied successfully for both purposes ; namely to dissolve L1PO ₂ F ₂ when LiF is present as main impurity, and to dissolve preferentially LiPF ₆ if it is the main impurity contained in the reaction mixture comprising LiP0 ₂ F ₂ as main product. It was found that LiF is only very sparingly soluble in aprotic organic solvents and that LiPF ₆ has a comparably good solubility while the solubility of L1PO ₂ F ₂ is in between.

Solvents for both purposes which are generally aprotic polar organic solvents, are known. Solvents which are useful as electrolyte solvents in lithium ion batteries can be applied. They are preferred because they would not have a detrimental effect on battery electrolytes or could even be used to provide bttery electrolytes. Such solvents are generally known. Preferably, a solvent suitable as electrolyte solvent in lithium ion batteries is applied to extract LiPF ₆ .

In the following, preferred organic aprotic solvents for the workup of reaction mixtures are presented in detail.

Organic carbonates, especially dialkyl carbonates, e.g. dimethyl carbonate or diethyl carbonate, methyl ethyl carbonate, alkylene carbonate, e.g. ethylene carbonate or propylene carbonate, fluorinated solvents, e.g. mono-, di-, tri- and/or tetrafluoroethylene carbonate, are very suitable. Instead or additionally, the extraction of L1PO ₂ F ₂ from mixtures with LiF or, respectively, of LiPF ₆ from mixtures comrising L1PO ₂ F ₂ may be performed with other solvents, for example, lactones, formamides, pyrrolidinones, oxazolidinones, nitroalkanes,

Ν,Ν-substituted urethanes, sulfolane, dialkyl sulfoxides, dialkyl sulfites, as described in the publication of M. Ue et al. in J. Electrochem. Soc.

Vol. 141 (1994), pages 2989 to 2996, or trialkylphosphates or alkoxyesters, as described in DE-A 10016816.

Alkyl carbonates with linear and branched alkyl groups and alkylene carbonates are especially suitable for preferentially dissolving L1PO ₂ F ₂ in mixtures comprising LiF, and of LiPF ₆ in mixtures comprising L1PO ₂ F ₂ , respectively, for example, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate (EMC), diethyl carbonate, and propylene carbonate (PC), see

EP-A-0 643 433. Pyrocarbonates are also useful, see US-A 5,427,874. Alkyl acetates, for example, ethyl acetate, N,N-di substituted acetamides, sulfoxides, nitriles, glycol ethers and ethers are useful, too, see EP-A-0 662 729. Often, mixtures of these solvents are applied. Dioxolane is a useful solvent, see EP-A-0 385 724. For lithium bis-(trifluoromethansulfonyl)imide, 1,2-bis-

(trifluoracetoxy)ethane and Ν,Ν-dimethyl trifluoroacetamide, see ITE Battery Letters Vol.1 (1999), pages 105 to 109, are applicable as solvent. In the foregoing, the term "alkyl" preferably denotes saturated linear or branched CI to C4 alkyl groups ; the term "alkylene" denotes preferably C2 to C7 alkylene groups, including a vinylidene group, wherein the alkylene group preferably comprises a bridge of 2 carbon atoms between the oxygen atoms of

the -0-C(0)-0- group, thus forming a 5-membered ring.

Fluorosubstituted compounds, for example, fluorinated carbonic esters which are selected from the group of fluorosubstituted ethylene carbonates, fluorosubstituted dimethyl carbonates, fluorosubstituted ethyl methyl carbonates, and fluorosubstituted diethyl carbonates are also suitable solvents for dissolving L1PO ₂ F ₂ or LiPF ₆ , respectively. They are applicable in the form of mixtures with non-fluorinated solvents. The non-fluorinated organic carbonates mentioned above are for example very suitable.

Preferred fluorosubstituted carbonates are monofluoroethylene carbonate, 4,4-difluoro ethylene carbonate, 4,5-difluoro ethylene carbonate, 4-fluoro-4- methyl ethylene carbonate, 4,5-difluoro-4-methyl ethylene carbonate, 4-fluoro-5- methyl ethylene carbonate, 4,4-difluoro-5-methyl ethylene carbonate,

4-(fluoromethyl)-ethylene carbonate, 4-(difluoromethyl)-ethylene carbonate, 4-(trifluoromethyl)-ethylene carbonate, 4-(fluoromethyl)-4-fluoro ethylene carbonate, 4-(fluoromethyl)-5-fluoro ethylene carbonate, 4-fluoro-4, 5 -dimethyl ethylene carbonate, 4,5-difluoro-4,5-dimethyl ethylene carbonate, and

4,4-difluoro-5,5-dimethyl ethylene carbonate ; dimethyl carbonate derivatives including fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis(fluorom ethyl) carbonate,

bis(difluoro)methyl carbonate, and bis(trifluoro)methyl carbonate ; ethyl methyl carbonate derivatives including 2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate, 2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethyl carbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyl difluoromethyl carbonate, and ethyl trifluoromethyl carbonate ; and diethyl carbonate derivatives including ethyl (2-fluoroethyl) carbonate, ethyl

(2,2-difluoroethyl) carbonate, bis(2-fluoroethyl) carbonate, ethyl

(2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl 2'-fluoroethyl carbonate, bis(2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl 2'-fluoroethyl carbonate, 2,2,2-trifluoroethyl 2',2'-difluoroethyl carbonate, and bis(2,2,2-trifluoroethyl) carbonate. Carbonic esters having both an unsaturated bond and a fluorine atom (hereinafter abbreviated to as "fluorinated unsaturated carbonic ester") can also be used as solvent to remove LiPF ₆ from its mixture with L1PO ₂ F ₂ or to dissolve L1PO ₂ F ₂ to separate it from impurities, e.g. impurities like LiF. The fluorinated unsaturated carbonic esters include any fluorinated unsaturated carbonic esters that do not significantly impair the advantages of the present invention.

Examples of the fluorinated unsaturated carbonic esters include fluorosubstituted vinylene carbonate derivatives, fluorosubstituted ethylene carbonate derivatives substituted by a substituent having an aromatic ring or a carbon-carbon unsaturated bond, and fluorosubstituted allyl carbonates.

Examples of the vinylene carbonate derivatives include fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate and 4-fluoro-5-phenylvinylene carbonate.

Examples of the ethylene carbonate derivatives substituted by a substituent having an aromatic ring or a carbon-carbon unsaturated bond include 4-fluoro-4- vinylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4,4-difluoro-4- vinylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4-fluoro-4,5- divinylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4-fluoro- 4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro- 5 -phenyl ethylene carbonate, 4,5-difluoro-4-phenylethylene carbonate and 4,5-difluoro-4,5-diphenylethylene carbonate.

Examples of the fluorosubstituted phenyl carbonates include fluoromethyl phenyl carbonate, 2-fluoroethyl phenyl carbonate, 2,2-difluoroethyl phenyl carbonate and 2,2,2-trifluoroethyl phenyl carbonate.

Examples of the fluorosubstituted vinyl carbonates include fluoromethyl vinyl carbonate, 2-fluoroethyl vinyl carbonate, 2,2-difluoroethyl vinyl carbonate and 2,2,2-trifluoroethyl vinyl carbonate.

Examples of the fluorosubstituted allyl carbonates include fluoromethyl allyl carbonate, 2-fluoroethyl allyl carbonate, 2,2-difluoroethyl allyl carbonate and 2,2,2-trifluoroethyl allyl carbonate.

The extraction of L1PO ₂ F ₂ from mixtures containing LiF as impurity and the extraction of LiPF ₆ as impurity from mixtures also containing L1PO ₂ F ₂ , respectively, may be performed in a known manner, for example, by stirring the reaction mixture with the solvent (extractant) directly in the reactor, or after removing the reaction mixture from the reactor and optionally crushing or milling, in a suitable vessel, e.g. a Soxhlet vessel. The extraction liquid contains a Li salt and may be further processed.

If the separation process served to remove LiPF ₆ from L1PO ₂ F ₂ , the liquid phase containing LiPF ₆ dissolved in the solvent can be separated from the non- dissolved L1PO ₂ F ₂ in a known manner. For example, the solution can be passed through a filter, or it can be decanted, or the separation can be effected by centrifugation. If desired, LiPF ₆ can be recovered by removing the solvent, e.g. by evaporation.

The remaining undissolved L1PO ₂ F ₂ can be stored or can be subjected to further purification treatments to obtain pure solid L1PO ₂ F ₂ . This can be performed in a known manner. For example, adhering solvent can be removed by evaporation which may preferably be performed in a vacuum depending on the boiling point of the adhering solvent or solvents.

If the separation process served to dissolve L1PO ₂ F ₂ , the solid phase remaining after extraction can be separated in a known manner from the extracting solvent containing dissolved L1PO ₂ F ₂ . For example, the solution containing L1PO ₂ F ₂ can be passed through a filter, or it can be decanted, or the separation can be effected by centrifugation. The undissolved residue contains essentially all LiF which can be recovered in pure form for example by re- crystallisation.

The dissolved L1PO ₂ F ₂ can be recovered from the solution by evaporation of the solvent to obtain pure solid L1PO ₂ F ₂ . This can be performed in a known manner. For example, adhering solvent can be removed by evaporation which may preferably be performed in a vacuum depending on the boiling point of the adhering solvent or solvents.

If the reaction mixture contains L1PO ₂ F ₂ and significant amounts of both LiF and LiPF ₆ , it is preferred first to remove LiPF ₆ with a solvent preferentially dissolving LiPF ₆ , and then to apply a solvent which preferentially dissolves L1PO ₂ F ₂ over LiF. It is possible to apply the same solvent and to perform a step-wise purification. In the first step, LiPF ₆ is dissolved by treating the reaction mixture with the solvent which preferably is one of those mentioned above. Due tio the good solubility of LiPF ₆ it will be dissolved first and can thus be removed from the reaction mixture. The reaction mixture recovered from the first treatment step is then again treated with a solvent which is preferably one of those mentioned above. Now, L1PO ₂ F ₂ is preferentially dissolved. LiF remains as solid. Dissolved L1PO ₂ F ₂ can then recovered from the solution as mentioned above. The isolated L1PO ₂ F ₂ can be used as additive for the manufacture of lithium ion batteries. It can also be used as additive for Li-sulfur batteries and for Li-oxygen batteries or Li-air batteries.

Isolated solid L1PO ₂ F ₂ can be re-dissolved in any suitable solvent or solvent mixture. The solvents mentioned above, including acetone and dimethoxyethane, are very suitable. Since its main use is as electrolyte salt or salt additive in the field of lithium ion batteries, it may be preferably dissolved in a water-free solvent used for the manufacture of the electrolyte solutions of lithium ion batteries. Such solvents are disclosed above.

A solution of L1PO ₂ F ₂ in propylene carbonate for example contains, under standard conditions (25°C, 1 Bara), up to about 3 % by weight of L1PO ₂ F ₂ relative to the total weight of the solution. In other solvents or solvent mixtures, the amount of L1PO ₂ F ₂ which dissolves at a given temperature will vary but can easily be determined by simple tests.

Other highly suitable solvents with a high dissolving power for L1PO ₂ F ₂

(e.g. dimethoxyethane and acetonitrile) are given above.

The advantage of the processes of the invention is that the reaction speed is very high even at ambient temperature. Pure crystalline L1PO ₂ F ₂ can be obtained from cheap starting material, for example, when extracted from the reaction mixture containing L1PO ₂ F ₂ and LiF with dimethyl carbonate or propylene carbonate as solvent and subsequent removal of the solvent, e.g. in a vacuum.

An advantage of using POF ₃ is that it can be prepared essentially free of HC1 even in chlorine-fluorine exchange reactions. Since the boiling point (b.p.) of POF ₃ , -40°C, is higher than that of HC1 (the b.p. of HC1 is -85.1°C) in contrast to PF ₅ (the boiling point of which is -84.4°C which is similar to that of HC1), a simple distillation or condensation technique under pressure can be used for purification of the POF ₃ intermediate product, which makes the present process more economical.

Another aspect of the present invention is the use of POF ₃ for the manufacture of L1PO2F2.

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.

The following examples will describe the invention in further detail without the intention to limit it. Example 1 : Synthesis and isolation of L1PO ₂ F ₂ using PF ₅ as P-F bond containing compound

5 g L1 ₃ PO ₄ were given into an autoclave. Gaseous PF ₅ was introduced into the reactor. An immediate pressure drop was observed which was allocated to the consumption of PF ₅ in the reaction with L1 ₃ PO ₄ forming L1PO ₂ F ₂ and LiF. Further PF ₅ was introduced into the autoclave until the pressure remained at about 3 to 4 bar (abs.) indicating that no further reaction occurred. After removal of the gaseous phase, the remaining solid had a weight of 12 g and was analyzed with XRD. The characteristic signals of L1PO ₂ F ₂ , of LiF and of LiPF ₆ were identified. For the isolation of L1PO ₂ F ₂ , the solid can be heated to about 200°C to decompose any LiPF ₆ to form LiF and PF ₅ ; after removal of the PF ₅ , the remaining solid essentially consists of L1PO ₂ F ₂ and LiF. The solid is given into a Soxhlet vessel and be extracted with dimethyl carbonate. From the combined solutions, the solvent is removed by evaporation in a rotary evaporator, and the resulting solid is subjected to analysis by XRD, F-NMR and P- MR.

Analytical data of L1PO2F2 :

• XRD:2-Theta values : 21.5 (strong) ; 22.0 ; 23.5 ; 27.0 (strong) ; 34.2 ; 43.2

• ¹⁹ F- MR (470.94 MHz ; solution in D-acetone) : -84.25 ppm (doublet, the 2 lines at -83.3 ppm and -85.2 ppm, coupling constant 926 Hz)

· ³¹ P- MR (202.61 MHz ; solution in D-acetone) : -19,6 ppm (triplet,

the 3 lines at -12.3 ppm, -16.9 ppm and -21.5 ppm ; coupling constant 926 Hz).

Example 2 : Electrolyte solution for lithium ion batteries, lithium-sulfur batteries and lithium-oxygen batteries

23 g of LiP0 ₂ F ₂ , 117 g of LiPF ₆ , 50 g monofluoroethylene

carbonate ("F1EC") and propylene carbonate ("PP") are mixed in amount such that a total volume of 1 liter is obtained. The resulting solution contains

0.77 mol of LiPF ₆ and 0.23 mol L1PO ₂ F ₂ . Thus, the amount of lithium compounds is about 1 mol per liter and corresponds to the concentration of lithium salts commonly used for the batteries, especially lithium ion batteries.

Example 3 : Synthesis and isolation of L1PO ₂ F ₂ using POF ₃ as P-F bond containing compound

3.5 g L1 ₃ PO ₄ were given into an autoclave. Gaseous POF ₃ was introduced into the reactor. An immediate pressure drop was observed which was allocated to the consumption of POF ₃ in the reaction with L1 ₃ PO ₄ forming L1PO ₂ F ₂ .

Further POF ₃ was introduced from a separate metal container with a final pressure of around 6 atm which decreased continuously. The temperature of the vessel was raised up to 80°C for one hour, and then the gas connection was interrupted and the reaction mixture was cooled down to room temperature while the excess gas phase was pumped off.

After removal of the gaseous phase, the remaining white solid had a weight of 5.7 g and was analyzed with XRD. The characteristic signals of only L1PO ₂ F ₂ were identified. The solid is given into a Soxhlet vessel and be extracted with dimethyl carbonate. From the combined solutions, the solvent is removed by evaporation in a rotary evaporator, and the resulting solid is subjected to analysis by XRD, F-NMR and P- MR.

The analytical data of L1PO ₂ F ₂ obtained in example 3 corresponded to those of L1PO ₂ F ₂ obtained in example 1.

Example 4 : Electrolyte solution for lithium ion batteries, lithium-sulfur batteries and lithium-oxygen batteries

117 g of LiPF ₆ , 23 g of L1PO ₂ F ₂ obtained analogously to example 3, 50 g monofluoroethylene carbonate ("F1EC") and propylene carbonate ("PP") are mixed in amount such that a total volume of 1 liter is obtained. The resulting solution contains 0.77 mol of LiPF ₆ and 0.23 mol L1PO ₂ F ₂ . Consequently, the amount of lithium compounds is about 1 mol per liter and thus corresponds to the concentration of lithium salts commonly used for the batteries, especially lithium ion batteries.