This application claims priority to European patent application

No. 11178672.9, filed on 24 August 2011, the whole content of this application being incorporated herein by reference for all purposes.

The present invention concerns fluoroalkyl S-(fluoro)alkyl thiocarbonates, a method for the preparation of fluoroalkyl S-(fluoro)alkyl thiocarbonates (i.e. fluoroalkyl S-alkyl thiocarbonates and fluoroalkyl S-f uoroalkyl

thiocarbonates - the term in brackets denotes an optional fluorine substitution), especially of fluoromethyl S-methyl thiocarbonate ; and their use as solvent additives for Li ion batteries.

S-alkyl thiocarbonate is a known solvent additive for lithium ion batteries.

Object of the present invention is to provide novel additives for Li ion battery solvents. This object and other objects, i.a. a method which allows the selective manufacture of monofluorinated fluoroalkyl S-alkyl thiocarbonates and mono fluoroalkyl S-fluoroalkyl thiocarbonates, namely fluoroalkyl S-alkyl thiocarbonates and especially fluoromethyl S-methyl thiocarbonate, are achieved by the present invention.

One aspect of the invention concerns fluoroalkyl S-(fluoro)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-SR',

wherein R denotes H ; linear or branched alkyl with 1 to 5 C atoms, CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH, CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ , or

CH = CHY wherein Y is H, CH ₃ or C2H5 ; and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; linear or branched alkyl with 2 to 7 carbon atoms, substituted by at least one fluorine atom ; CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ ; phenyl ; phenyl, substituted by 1 or more CI to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms ; or benzyl.

Preferably, R is H. allyl, methyl, ethyl or isopropyl.

Preferably, R' denotes CI to C5 alkyl, allyl or 2,2,2-trifluoroethyl.

Preferably, R' is methyl, ethyl, or n-propyl , isopropyl allyl or

2,2,2-trifluoroethyl.

Most preferred compounds are fluoromethyl S-methyl thiocarbonate, a-fluoroethyl S-methyl thiocarbonate, fluoromethyl S-2,2,2-trifluoroethyl thiocarbonate, α-fluoroethyl S-2,2,2-trifluoroethyl thiocarbonate and

fluoromethyl S-allyl thiocarbonate.

Another aspect of the present invention concerns a method for the manufacture of fluoroalkyl S-(fluoro)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-SR',

wherein R denotes H ; linear or branched alkyl with 1 to 5 C atoms, CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH, CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ , or CH = CHY wherein Y is H, CH ₃ or C2H5 ; and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; linear or branched alkyl with 2 to 7 carbon atoms, substituted by at least one fluorine atom ; CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ ; phenyl ; phenyl, substituted by 1 or more C 1 to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms ; or benzyl

which method comprises a step of reacting a fluoroalkyl fluoroformate of formula (II), FCHROC(0)F, or a fluoroalkyl chloro formate of formula (IF), FCHROC(0)Cl, with a thioalcohol of formula (III), R'SH, wherein R and R' have the meanings given above, or

which method comprises a step of reacting a chloroalkyl fluoroformate of formula (IV), C1CHR0C(0)F, or a chloroalkyl chloroformate of formula (IV), C1CHR0C(0)C1, wherein R has the meaning given above, with a thioalcohol of formula (III), R'SH wherein R' has the meaning given above, and a subsequent chlorine- fluorine exchange.

Preferably, the method according to the present invention provides for the manufacture of fluoroalkyl S-(fluoro)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-SR' wherein R denotes H, linear or branched alkyl with 1 to 5 C atoms or and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; linear or branched alkyl with 2 to 7 carbon atoms, substituted by at least one fluorine atom ; allyl ; phenyl ; phenyl, substituted by 1 or more CI to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms ; or benzyl

comprising a step of reacting a fluoroalkyl fluoroformate of formula (II),

FCHROC(0)F, or a fluoroalkyl chloroformate of formula (IF), FCHROC(0)Cl, with a thioalcohol of formula (III), R'SH, wherein R and R' have the meanings given above, or

comprising a step of reacting a chloroalkyl fluoroformate of formula (IV), ClCHROC(0)F, or a chloroalkyl chloroformate of formula (IV),

ClCHROC(0)Cl, wherein R has the meaning given above, with a thioalcohol of formula (III), R'SH wherein R' has the meaning given above, and a subsequent chlorine- fluorine exchange.

An especially preferred embodiment of the present invention provides for the manufacture of fluoroalkyl S-(fluoro)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-OR' ,

wherein the method for the manufacture of fluoroalkyl S-(fluoro)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-SR' wherein R denotes linear or branched alkyl with 1 to 5 C atoms, CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH, CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ ; and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; allyl ; linear or branched alkyl with 2 to 7 carbon atoms, substituted by at least one fluorine atom ; phenyl ; phenyl, substituted by 1 or more C 1 to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms ; or benzyl

comprises a step of reacting a fluoroalkyl fluoroformate of formula (II), FCHROC(0)F, or a fluoroalkyl chloroformate of formula (IF), FCHROC(0)Cl, with a thioalcohol of formula (III), R'SH, wherein R and R' have the meanings given above.

The term "(fluoro)alkyl" preferably denotes alkyl groups, including groups substituted by groups of the structure CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH,

CH ₂ = CHX wherein X is a single bond, CH ₂ , or C ₂ H ₄ , allyl groups of the formula CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ ; and alkyl groups substituted by at least one fluorine atom. Consequently, the present invention provides monofluorosubstituted fluoroalkyl S-alkyl thiocarbonates and fluoroalkyl S-fluoroalkyl thiocarbonates wherein one fluoroalkyl group is monosubstituted and the other fluoroalkyl group may be substituted by one or more fluorine atoms. In fluoroalkyl S-fluoroalkyl thiocarbonates, the fluoroalkyl groups may be the same or different ; at least one of the fluoroalkyl groups is

mono fluorinated.

Instead of the thioalcohol or additionally to the thioalcohol, a respective alkali metal thioalcoholate can be applied, for example, the respective lithium, sodium, potassium or cesium thioalcoholate. It is preferred to manufacture thiocarbonates wherein R denotes CI to C3 alkyl, CH ₂ = CH-CH ₂ ,

CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH, or H, and more preferably, CI to C3 alkyl or H.

Thiocarbonates wherein R is H are especially preferred. According to this preferred embodiment, a method is provided for the manufacture of fluoromethyl S-(fluoro)alkyl thiocarbonates said method comprising a step of reacting fluoromethyl fluoroformate or fluoromethyl chloroformate and a thioalcohol, or, in an alternative, to react chloromethoxy chloroformate with a thioalcohol and to perform a subsequent chlorine fluorine exchange. It is especially preferred to use fluoromethyl fluoroformate which has the formula FCH ₂ -0-C(0)F.

The invention will now be explained in detail in view of the preferred alternative, namely the preparation of fluoroalkyl S-(fluoro)alkyl thiocarbonates from fluoromethyl fluoroformate and a thioalcohol ; also in this embodiment, the thioalcohol can be partially or completely be substituted by the respective alkali metal thioalcoholate, for example, by lithium, sodium, potassium or cesium thioalcoholate. The thioalcohol preferably denotes a CI to C5 thioalcohol ; a C2 to C5 thioalcohol substituted by at least one fluorine atom ; allyl thioalcohol. Preferably, R' is a linear or branched CI to C5 alkyl group, and thus, the thioalcohol is a CI to C5 alkanethiol, more preferably, it is methanethiol, ethanethiol, n-propanethiol, i-propanethiol, allyl thioalcohol, n-butanthiol, i-butanethiol, 2-methylpropanethiol, n-pentanethiol, i-pentanethiol, or

2,2,2-trifluoroethanethiol. If trifluoroethanethiol is applied, it is possible to produce thiocarbonates which comprise fluorine substituents on both substituent groups, for example, fluormethoxy-S-(2,2,2-trifluoroethyl)carbonate or

(l-fluoroethyl)-S-(2,2,2-trifluoroethyl)carbonate. Especially preferably, the thioalcohol is methanethiol, ethanethiol, allyl thioalcohol, n-propanethiol and i-propanethiol. The most preferred thioalcohol is methanethiol.

If desired, a mixture of thioalcohols can be applied in a desired molar ratio. For example, a mixture of methanethiol and ethanethiol can be applied in a molar ratio of 1 : 1. In this case, a mixture of the respective thiocarbonate substituted by a methylgroup and thiocarbonate substituted by an ethyl group is obtained.

The thioalcoho lysis reaction can be performed in the presence of an HF scavenger e.g. LiF, NaF, KF or CsF, or in the presence of base, e.g. in the presence of ammonia or a primary, secondary or tertiary amine,

e.g. triethylamine or pyridine. Preferably, it is performed in the absence of a base.

The molar ratio between thioalcohol and formate preferably is equal to or greater than 0.9: 1. Preferably, it is equal to or lower than 5: 1. Very good results are achieved when the ratio of thioalcohol and formate is in the range of 0.95 : 1 to 1.2: 1.

The reaction temperature during the thioalcoho lysis reaction is not critical.

Often, the reaction is exothermic, thus, it may be advisable even to cool the reaction mixture, especially if an alkali metal thioalcoholate is applied. The temperature during thioalcoho lysis is preferably equal to or higher than - 80°C, more preferably, equal to or higher than -78°C. The upper temperature can be dependent from pressure and boiling point of the starting materials, e.g. from the boiling point of the thioalcohol. Often, the temperature is equal to or lower than 85°C.

The reaction can be performed in any suitable reactor, e.g. in an autoclave.

The reaction can be performed batch wise or continuously.

The resulting reaction mixture can be separated by known methods, e.g. by distillation, precipitation and/or crystallization. If desired, the reaction mixture can be contacted with water to remove water-soluble constituents. Due to the specific type of reaction, organic carbonates with a higher degree of fluorination are formed, if at all, in only very minor proportions.

According to another alternative, fluoroalkyl S-(fluor)alkyl thiocarbonates of the general formula (I), FCHR-OC(0)-SR' wherein R and R' have the meaning given above are prepared in a method

comprising a step of reacting a chloroalkyl fluoroformate of formula (IV), C1CHR0C(0)F, or a chloroalkyl chloroformate of formula (IV),

C1CHR0C(0)C1, wherein R has the meaning given above, with a thioalcohol of formula (III), R'SH wherein R' has the meaning given above, and a subsequent chlorine- fluorine exchange.

Thus, in a first step, an intermediate thiocarbonate of formula (V), C1CHR-0C(0)-SR', is produced. In this formula (V), R and R' have the meanings given above. This intermediate thiocarbonate is then reacted with a reactant capable of substituting a fluorine atom for the chlorine atom. This reaction is known as "Halex" reaction. Reactants suitable to perform a chlorine- fluorine exchange are generally known. Especially suitable as such a reactant are alkaline or alkaline earth metal fluorides, ammonium fluoride, amine hydrofluorides of formula (IX), IN^R^F wherein the substituents R ¹ are the same or different and denote H or CI to C5 groups with the proviso that at least 1 substituent R ¹ is a CI to C5 alkyl group. Also amine hydrofluorides are suitable in which the nitrogen atom is part of a heterocyclic ring system, for example, pyridinium hydrofluoride, l,8-diazabicyclo[5.4.0]undec-7-ene, and 1,5-diaza- bicyclo[4.3.0]non-5-ene. Instead of the fluorides, or additionally to them, hydrofluoride adducts can be used for the Halex reaction, e.g. CsF HF. Other fluorides are likewise suitable as reactant, e.g. AgF. The Halex reaction can be performed in the absence or in the presence of a solvent, for example, in the presence of a nitrile. Often, the reaction is performed at elevated temperature, e.g. at a temperature equal to or higher than 50°C.

The workup of the reaction mixture which comprises the chloride salt and possibly excess fluoride salt of the fluorinating reactant, and the fluorinated carbonate and possibly unreacted starting material, is performed in a known manner. For example, solids are removed by filtration, and the liquid phase is subjected to a fractionated distillation or precipitation after removal of any solvents.

The fluorinated organic thiocarbonates produced by the method of the present invention are useful as additives or solvents for lithium ion batteries, lithium-air batteries and lithium- sulfur batteries. They provide advantages like modifying the viscosity, reduce flammability and appear to modify the electrodes under formation of beneficial films. Consequently, another aspect of the present invention concerns the use fluoroalkyl S-(fluoro)alkyl thiocarbonate of general formula (I), FCHR-OC(0)-SR', wherein R denotes H ; linear or branched alkyl with 1 to 5 C atoms, CH ₂ = CHX wherein X is CH ₂ , C ₂ H ; CH(CH ) = CH, C(CH ₃ ) ₂ = CH ; or CH=CHY wherein Y is H ; CH ₃ or CH ₅ ; and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; linear or branched alkyl with 1 to 7 carbon atoms, substituted by at least one fluorine atom ; phenyl ; phenyl, substituted by 1 or more CI to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms ; or benzyl,

as additive or as solvent for Li ion batteries, Li air batteries and Li sulfur batteries.

Compounds of formula (II), FCHROC(0)F, can be prepared from the respective chloroalkyl chloroformates in a "Halex" type reaction, i.e. substitution of fluorine atoms for the chlorine atoms by fluorinating agents, as already described above, e.g. using a fluorinating reactant like alkali or alkaline earth metal fluorides, e.g. LiF, KF, CsF, NaF, NH ₄ F or amine hydro fluorides, or the respective HF adducts. The chloroalkyl chloroformates themselves are available through the reaction between phosgene and an aldehyde as described in

US patent 5,712,407. It is preferred to produce the intermediate compounds of formula (II), FCHROC(0)F, from carbonyl fluoride and an aldehyde. Thus, another aspect of the present invention concerns a method for the manufacture of intermediate compounds of formula (II), FCHROC(0)F, from carbonyl fluoride and an aldehyde of formula RC(0)H wherein R denotes linear or branched alkyl with 1 to 5 C atoms or H. Preferably, it denotes H ; here, the aldehyde is formaldehyde. The formaldehyde can be can be applied in the form of paraformaldehyde or trioxane which must be cracked, e.g. thermally, to form the monomeric formaldehyde.

The molar ratio between carbonyl fluoride and the aldehyde is preferably equal to or greater than 0.9: 1. It is preferably equal to or lower than 5: 1.

Preferably, the molar ratio between carbonyl fluoride and aldehyde is in the range of 0.9: 1 to 5 : 1. More preferably, the molar ratio between carbonyl fluoride and aldehyde is in the range of 0.9: 1 to 3 : 1.

Preferably, the reaction between carbonyl fluoride and the aldehyde is catalyzed, for example, by F ^~ . For example, the reaction can be catalyzed by HF, which may be added as such or prepared in situ by the addition of low amounts of water.

Preferred catalysts are those which contain fluoride anions, e.g. alkaline earth metal fluorides or alkali metal fluorides such as CsF, or catalysts which contain fluoride ions formed from carbonyl fluoride and a pre-catalyst. Preferred pre-catalysts are dialkyl formamides, especially dimethyl formamide. It is assumed that the formamide and carbonyl fluoride form a "naked" fluoride ion which starts a nucleophilic reaction on the aldehyde. The negatively charged oxygen of the formed adduct of the fluoride ion and the aldehyde molecule then reacts with a carbonyl fluoride molecule forming fluoromethyl fluoro formate or generally, the fluoro alky 1 fluoro formate.

Pyridine, advantageously 4-dialkylaminopyridines, especially

4-dimethylaminopyridine, are also considered as suitable pre-catalysts.

The reaction preferably is performed batch wise, e.g. in an autoclave.

Alternatively, it can be performed continuously.

The reaction temperature can vary. For example, when a very effective catalyst is applied, the reaction may even be performed at ambient temperature.

It has to be kept in mind, however, that in the case of formaldehyde as starting material, the monomeric form must be provided by cracking of

paraformaldehyde or 1,3,5-trioxane. Thus, while the reaction as such often could be performed at low temperature, nevertheless heat must be applied for cracking.

In the case of formaldehyde as starting material, the reaction preferably is performed at a temperature equal to or higher than 100°C. It is preferably performed at a temperature equal to or lower than 300°C. When aldehydes are used as starting material which must not be thermally cracked, the reaction can be performed at a temperature equal to or higher than 0°C and equal to or lower than 200°C. It is preferred to perform the reaction at such an elevated temperature and/or for a sufficient time until the desired conversion has taken place.

It is performed in the liquid phase or under supercritical conditions. The pressure is selected such that at least a part of the carbonyl fluoride is present in the liquid phase. The pressure depends from the reaction temperature ; the higher the reaction temperature, the higher is the pressure in the reactor. The reaction can be performed at ambient pressure (about 1 Bar absolute). For example, COF ₂ can be introduced into the liquid reaction mixture or starting material though an immersed pipe. Preferably, the reaction is performed at a pressure equal to or higher than 5 bar (abs.). Preferably, the reaction is performed at a pressure equal to or lower than 50 bar (abs.). If, as done in one example, the reaction temperature is sufficiently high, the content of the reactor is in a supercritical state. The reaction vessel can be pressurized, if desired, with an inert gas, especially with nitrogen.

If desired, the fluoroalkyl fluoroformates, and especially the fluoromethyl fluoroformate, can be isolated from the reaction mixture according to methods known in the art, e.g. by distillation. The fluorosubstituted formates formed can be applied for any purposes for which compounds with a C(0)F function or a FCH ₂ 0 function are used. For example, they can be used as fluorinating agent or to introduce a protecting group in aminoacids or peptides. In a preferred embodiment, the formates are reacted, as described above, with a thioalcohol to produce fluoromethyl S-alkyl esters, allyl esters or 2,2,2-tifluoroethyl esters of thiocarbonic acid.

A preferred aspect of the present invention concerns a method comprising 2 or 3 steps for the manufacture of compounds of formula (I), FCHROC(0)-SR', wherein R denotes H ; linear or branched alkyl with 1 to 5 C atoms or H and R' denotes linear or branched alkyl with 1 to 7 carbon atoms ; linear or branched alkyl with 2 to 7 carbon atoms substituted by at least one fluorine atom ;

CH ₂ = CHX wherein X is CH ₂ , C ₂ H ₄ ; phenyl ; benzyl ; phenyl, substituted by 1 or more C 1 to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine atoms. This method is performed according to two alternatives.

The first alternative comprises : A step of preparing a fluoroalkyl fluoroformate of formula (II),

FCHROC(0)F, from carbonyl fluoride and an aldehyde RC(0)H wherein R denotes linear or branched alkyl with 1 to 5 C atoms or H ; and

a step of reacting the fluoroalkyl fluoroformate of formula (II) with a thioalcohol of formula (III), R'SH, wherein R and R' have the meanings given above.

Instead of the thioalcohol or additionally to the thioalcohol, the respective alkali metal thioalcoholate can be applied, for example, the respective potassium or sodium thioalcoholate.

Also here, the group R preferably denotes H, and the aldehyde concerned is formaldehyde. The formaldehyde can be applied in the form of

paraformaldehyde or 1,3,5-trioxane which must be cracked, e.g. thermally, to form the monomeric formaldehyde.

A preferred embodiment of this 2-step method according to the present invention provides for the manufacture of fluoromethyl alkyl carbonates comprising :

A step of preparing fluoromethyl fluoroformate from carbonyl fluoride and formaldehyde, 1,3,5-trioxane or paraformaldehyde, and, with or without isolation, and subsequently,

A step of reacting the fluoromethyl fluoroformate with a thioalcohol of formula (III), R'SH, wherein R' preferably denotes linear or branched alkyl with 1 to 7 C atoms ; CH ₂ = CHX wherein X is CH ₂ or C ₂ H ₄ ; CH(CH ₃ ) = CH, C(CH ₃ ) ₂ = CH ; phenyl ; phenyl, substituted by 1 or more CI to C3 alkyl groups atoms or phenyl substituted by 1 or more chlorine or fluorine. Preferably, the thioalcohol is selected from the group consisting of methanethiol, ethanethiol, n-propanethiol, i-propanethiol, allyl thioalcohol, n-butanethiol and n- pentanethiol. Especially preferably, the thioalcohol is allyl thioalcohol, methanethiol, 2.2.2-trifluoroethanethiol, or ethanethiol, and most preferably, methanethiol.

Preferred embodiments of the steps are those already described above, especially what concerns the preferred use of a catalyst, using a formamide, especially dimethyl formamide, as preferred pre-catalyst in the first step, the pressure and temperature in the first and second step, the optional use of a base in the second step, the respective pressures, reaction temperatures etc ; the preferred embodiments described above for the respective reaction steps apply also for the 2-step method of the invention. The other alternative comprises a method which includes a Halex reaction.

In this alternative, in a first step, carbonyl chloride (phosgene) is reacted with RC(0)H wherein R denotes linear or branched alkyl with 1 to 5 C atoms or H. The formed intermediate chloroalkyl chloroformate of formula (IV), C1CHRC(0)C1 wherein R has the meaning given above is then either subjected to a Halex reaction to form the fluoroalkyl formate of formula (I) which is then reacted with an thioalcohol or a thioalcoholate as described above to produce the fluoroalkyl S-(fluoro)alkyl thio carbonates of formula (I) ; or the formed intermediate chloroalkyl chloroformate of formula (VII), C1CHR0C(0)C1 wherein R has the meaning given above, is then reacted with a thioalcohol or a thioalcoholate as described above to produce the chloroalkyl S-(fluoro)alkyl thiocarbonate of formula (V) which then is subjected to a Halex reaction as described above to produce the fluoroalkyl S-(fluoro)alkyl thiocarbonates of formula (I).

Another embodiment of the present invention are chloroalkyl S-fluoroalkyl thiocarbonate intermediates of formula (V), C1CHRC(0)SR" wherein R denotes H ; linear or branched alkyl with 1 to 5 C atoms ; and wherein R' ' denotes linear or branched alkyl with 1 to 7 carbon atoms, substituted by at least one fluorine atom. Preferably, in compounds of formula (V), R denotes C¾ or H, and R' ' denotes S-2,2,2-trifluoroethyl.

These intermediates can be prepared from 1 -chloroalkyl chloro formates and a fluorinated thioalcohol or the thioalcoholate, e.g. the lithium, sodium, potassium or cesium thioalcoholate of a fluorinated thioalcohol ;

trifluorothioethanolates are possibly instable. These intermediates can be used, as described, as starting material to produce the fluoroalkyl S-fluoroalkyl thiocarbonates of the present invention. They can also be used as intermediates in chemical synthesis.

The method of the present invention concerning the preparation of fluoromethyl S-alkyl thiocarbonates allows for the selective production of mono fluorinated products ; likewise, the preparation of fluoromethyl S- fluoroalkyl thiocarbonates allows for the selective production of thiocarbonates wherein both substituents are substituted by a defined amount of F ions ;

undesirably higher fluorinated products are formed, if at all, in only minor amounts.

Since a main application field for the compounds of formula (I) is the use as solvents or additives in lithium ion batteries, it is preferred not start from chlorinated compounds because chlorine is undesired as impurity in the technical field. Thus, the reaction path without the necessity of Halex reactions is preferred.

The compounds can be used neat as a solvent in the Li ion batteries, or, preferably, together with one or more other solvents, as an additive, e.g. for reducing the viscosity of the solvent. The amount as an additive is, for example, in a range from 0.5 to 60 % by weight.

Suitable solvents are known. In the following, some preferred such solvents are given.

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 comprising 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, Ν,Ν-disubstituted 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(fluoromethyl) 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-phenylethylene 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 thio compounds of the invention have certain smell. Thus, they can be used as additive having a warning function indicating a damaged battery housing.

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

The invention will now be further described in examples without intending to limit it. Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

Examples :

Example 1 : Preparation of fluoromethyl fluoroformate

Paraformaldehyde (10.2 g ; 340 mmol) and dimethylformamide (1.5 g ; 71 mmol) were given into an autoclave with an internal volume of about 500 ml. The autoclave was closed, evacuated and pressurized to about 5 bar (abs.) with dry nitrogen and evacuated again. Then, carbonyl fluoride (32 g ; 485 mmol) was given into the autoclave. The autoclave was heated overnight to

about 230°C ; the pressure rose to about 35 bar (abs.). Then, the autoclave was cooled to ambient temperature, the pressure fell now to about 10 bar (abs.). Gaseous components of the autoclave were purged through a washer. The autoclave was then pressurized two times with nitrogen, each time up to a pressure of about 5 bar (abs.).

If desired, fluoromethyl fluoroformate formed can be isolated by distillation.

Example 2 : Preparation of O-fluoromethyl S-ethyl thiocarbonate

Fluoroethyl fluoroformate (50.0 g) was chilled to 0°C. Under stirring, a mixture of pyridine (12.0 g) and ethylthiol (28.2 g) was added. The progress of reaction was monitored by GC analysis. After 18 h, 50 mL of water were added. After phase separation the organic phase was washed with water and saturated sodium chloride solution. After drying over sodium sulfate the product was obtained as a slightly yellow colored liquid (45 g). The purity without any purification step was 73.5 %. The product can be further purified by distillation. Example 3 : Preparation of a- fluoroethyl fluoroformate

Acetaldehyde (12 g ; 272 mmol) and dimethylformamide (200 mg ;

71 mmol) were given into an autoclave with an internal volume of about 40 ml. The autoclave was closed, evacuated and pressurized to about 5 bar (abs.) with dry nitrogen and evacuated again. Then, carbonyl fluoride (18 g ; 272 mmol) was given into the autoclave over a period of 30 min. The mixture was stirred at room temperature for 30 min after which the pressure fell from 20 bar to 0 bar. The autoclave was then pressurized two times with nitrogen, each time up to a pressure of about 5 bar (abs.).

If desired, fluoroethyl fluoroformate formed can be isolated by distillation. Example 4 : Preparation of O-a-fluoroetfiyl S-methyl thiocarbonate

In a 100 mL PF A- flask a-fluoroethyl fluoroformate (24.7 g, 225 mmol) was cooled to 0°C. Methanethiol (310 mmol) is added over a period of 15 min. The mixture is stirred at -78°C for 30 min. After warming up to room temperature the reaction is stirred for further 16 h. The resulting mixture is washed with water (3 x 10ml), molecular sieve (0.4 nm) is added, and after stirring for 4 h at room temperature, all solids are removed by filtration. The resulting crude product may be purified by distillation under reduced pressure. Example 5 : Preparation of a-fluoroethyl S-ethyl thiocarbonate

In a 100 mL PF A- flask α-fluoroethyl fluoroformate (27.0 g, 245 mmol) is added to dry NaF (15 g ; 357 mmol). After cooling the mixture to 0°C ethanethiol (310 mmol) is added over a period of 15 min. The mixture is stirred at 0°C for 30 min. After warming up to room temperature the reaction is stirred for further 16 h. After addition of 5 g molecular sieve (0.4 nm) and stirring for 4 h at room temperature, all solids are removed by filtration. The resulting crude product may be purified by distillation under reduced pressure.

Example 6 : Electrolyte compositions containing F-alkyl S-alkyl thiocarbonates

To obtain the electrolyte compositions, in a first step, the solvent components of the base solvent (which may be a mixture of solvents) and the respective thiocarbonate indicated in table 1 are mixed under stirring ; then, the electrolyte salt is added and dissolved under stirring. All operations are performed under dry N ₂ or Ar.

* Into the solvent composition, LiPF ₆ is added in an amount such that the concentration of LiPF ₆ is 1 -molar. If LiP02F2 is added as electrolyte salt additive, it is added such that the content in the electrolyte composition is 1 % by weight, when the total weight of the composition including all solvents and electrolyte salt components is set to 100 % by weight. L1PO2F2 can be simply manufactured by the reaction between POF3 and Li3P04 according to the reaction

2 POF3 + L13PO4 -> 3 LiP0 ₂ F ₂ Such a reaction is described in unpublished EP patent application

N° 10188108.4 filed October 19, 2010. Other methods are known.

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. 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-A 2008-305402 also discloses preparation of L1PO ₂ F ₂ from LiPF ₆ with a carbonate compound.