DE10016816A1 - Use of alkoxy esters - Google Patents

Abstract

The invention relates to the use of the alkyl esters of 2-alkoxy-perfluorocarboxylic acids as solvents or components thereof for support electrolytes in electrolytes.

Description

The invention relates to a new application for certain alkoxy esters and mixtures with them.

Electrolytes from solvents or solvent mixtures for example, dissolved and dissolved conductive salts are in how of rechargeable batteries. Many different guides salts and many different organic solvents Manufacture of electrolytes are known. Some useful ones Compound classes are for example in J. Elektrochem. Soc. Vol. 141 (1994), pages 2989-2996. Frequently alkyl carbonates or alkylene carbonates are used, see EP-A-0 643 433. Pyrocarbonates can also be used, see US-A 5,427,874. Also alkyl acetates; N, N-disubstituted acet amides, sulfoxides, nitriles, glycol ethers and ethers are considered have been recognized as useful, see EP-A-0 662 729. Often Mixtures of such solvents are used, for example Mixtures with dioxolane, see EP-A-0 385 724. For lithium bis (trifluoromethanesulfonyl) imide were also 1,2-bis (trifluoro acetoxy) ethane and N, N-dimethyltrifluoroacetamide as a solution medium, see ITE Battery Letters Vol. 1 (1999), pages 105-109. US-A 5,976,731 discloses Lithi ion batteries and solvents for the conductive salt. As Carbazoles, phenothiazines, phenoxa are added as solvents zine, acridines, dibenzoazepines or phenazines used, the obviously stabilize the solution.

In general, it is desirable to have the largest possible Re Servoir of usable classes of compounds as solvents  for conductive salts in electrolytes. task The present invention is to make the range more useful To enlarge solvents for conductive salts. This task will solved by the present invention.

The invention is based on the knowledge that esters of certain carboxylic acids very well as solvents for Leit salts are useful for the formation of electrolytes.

According to the invention, esters of the formula (I) R ¹ -CF (OR ² ) -C (O) OR ^{3 are used} , in which R ^{1 is} CF ₃ , C ₂ F ₅ or C ₃ F ₇ and R ² and R ³ stand for C1-C4-alkyl or for partially or perfluorinated C1-C4-alkyl, as a solvent or in solvent mixtures for conductive salts in electrolytes. The electrolytes are used in particular for the production of rechargeable batteries.

It has been found that such esters are very good Have solvent power for conductive salts. Usually in batteries concentrations around 1 mol / l of the conductive salt in Solvent sought. It has been found in experiments that z. B. 2-methoxyperfluoropropionate without white teres dissolves as much lithium bis (trifluoromethanesulfonyl) imide, that its concentration is 1.9 mol / l. Advantage is therefore that even at lower temperatures in the Practice when using batteries can be achieved Failure of the conductive salt is not to be feared.

Certain esters are preferably used in the invention. R ¹ is preferably CF ₃ or C ₂ F ₅ , in particular CF ₃ . R ² and R ³ may be the same or different, the latter due to production, if a mixture of different alcohols is used (see below for the production method) or by transesterification of the compound of formula (I). Preference is given to using pure alcohols and R ² and R ³ are the same. R ² and R ³ are preferably alkyl atoms with 1 to 3 carbon atoms, in particular methyl or ethyl.

Esters in which R ² and R ^{3 are} identical or different and represent partially or perfluorinated C1-C4 alkali groups are also useful. Compounds in which R ² and R ^{3 are the} same and for partially fluorinated alkyl radicals, for. B. CF ₃ -CH ₂ , standing, can be prepared analogously to the non-fluorinated esters by using partially fluorinated alcohols. Esters with perfluorinated alkyl groups R ² and R ³ can gene by subsequent fluorination of partially or non-fluorinated compounds, for. B. be produced by electrofluorination. Ver compounds in which R ² for a non-fluorinated alkyl radical and R ³ for a partially fluorinated alkyl radical, for. B. CF ₃ CH ₂ , can by transesterification of an appropriate ester with z. B. Trifluoroethanol.

Preferred conductive salts are lithium salts. Lithium hexafluorophosphate, lithium tetra fluoroborate and lithium salts of sulfonylimides, for example the lithium salt of bis- (trifluoromethanesulfonyl) imide, are particularly useful. The conductive salts are expediently present in the solvent in a concentration of at least 0.5 mol / l. Usually who in the finished electrolyte concentrations of about 1 mol / l of conductive salt aimed. The upper limit is of course the saturation concentration. Other preferred salts are LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ and LiSO ₃ CF ₃ . LiAsF ₆ , LiSbF ₆ , LiClO ₄ and LiN (C ₂ F ₅ SO ₂ ) ₂ are also very useful.

The esters described here can be used in pure form, as a mixture of esters or as a mixture with other known known solvents for the production of electrolytes. As a further solvent, the solvents described as useful in the publications cited above can be used. The usable solvents are not limited to the classes of compounds mentioned there. Other commonly used solvents can also be used. Usable as co-solvents are, for example, those in the unpublished German patent application. , , (199 42 021.1) described dialkylamides of perfluorinated carboxylic acids. The compounds described there are C ₁ -C ₃ -dialkylamides, in particular trifluoroacetic acid. The like compounds exert a stabilizing effect in particular on lithium hexafluorophosphate. Other aprotic solvents, for example lactones, nitriles, formamides, acetamides, pyrrolidinones, oxazolidinones, nitroalkanes, N, N-substituted urethanes, sulfolanes, dialkyl sulfoxides, dialkyl sulfites and trialkyl phosphates, can also be used.

The invention further relates to electrolytes, the esters of the general formula (I) and conductive salts and ge optionally other aprotic solvents for conductive salts or contain stabilizing additives. The preferred Esters correspond to those preferred above Esters.

The use of the 2-alkoxy esters widens the range available solvent for conductive salts; the connections have the advantage that they have a very good solving power for conductive salts. The risk of ignition is reduced puts.

The preparation of the esters is known from the literature. You go from the corresponding perfluoroalkene-1,2-epoxides (Per fluoro-1,2-oxiranes). For the production of 2-alkoxy-per Fluoropropionic acid esters are based on hexafluoropropene oxide. These epoxides in turn can be caused by electrochemical fluo ration of the corresponding chlorohydrins or by chemical or photochemical oxidation of the perfluoroalkenes become.

The epoxides are then reacted with an alcohol. The desired 2-alkoxy-perfluoroalkyl is then formed carboxylic acid esters. The production of such esters is carried out by D. Sianesi, A. Pasetti and F. Tarli in J. Org. Chem. 31  (1966), pages 2312-2316; these authors quote on page 2312 also references, which the production of epoxides. A transesterification or subsequent Fluorination can be carried out if desired.

The following examples are intended to further illustrate the invention refine without restricting their scope.

example 1 Production of 2-methoxy-perfluoropropionic acid from Perfluoropropylene oxide and methanol

C ₃

F ₆

O + 2CH ₃

OH → CF ₃

CF (OCH _3rd

) COOCH ₃

+ 2HF

200 ml of methanol (4.94 mol; 32 g mol ^-1 ; 0.791 g cm ^-3 ) were placed in a 250 ml three-necked flask with dry ice reflux condenser and gas inlet at room temperature. Commercially available hexafluoropropylene oxide (24.2 g; 0.15 mol; 166 g mol ^-1 ) was slowly introduced. After 2 h the reaction mixture was poured into 100 ml of water and extracted three times with CH ₂ Cl ₂ . The combined organic phases were dried over Na ₂ SO ₄ and purified by distillation.
Kp: 44-46 ° C at 10 mbar
¹ H-NMR:
3.6 ppm (singlet, 3H, CH ₃ );
3.9 ppm (singlet, 3H, CH ₃ )
¹³ C-NMR:
54.10 ppm (singlet, 2 × CH ₃ ),
104.91 ppm (2 quartets, CF),
119.69 ppm (2 quartets, CF ₃ )
162.35 ppm (doublet, CO)
Yield: 53% of theory

literature

J. Org. Chem. 1966, 31, 2312-2316

Example 2 Manufacture of an electrolyte

Li [N (SO ₂ CF ₃ )] was dissolved in the 2-methoxy-perfluoropropionic acid methyl ester prepared according to Example 1. At 20 ° C, a concentration of 1.9 mol / l of the conducting salt was maintained. This is far greater than the commonly used concentration of 1 mol / l of the conducting salt.

Claims (8)

1. Use of esters of the formula (I)
R ¹ -CF (OR ² ) -C (O) OR ³ ,
wherein R ^{1 is} CF ₃ , C ₂ F ₅ or C ₃ F ₇ and R ² and R ^{3 are} C1-C4-alkyl or partially or perfluorinated C1-C4-alkyl, as solvents or in solvent mixtures for conductive salts in Electrolytes. 2. Use according to claim 1 of esters of the general formula (I), in which R ^{1 is} CF ₃ and R ² and R ^{3 are} identical or different and are alkyl having 1 to 3 carbon atoms. 3. Use according to claim 2, wherein R ^{1 is} CF ₃ and R ² and R ^{3 are} CH ₃ or C ₂ H ₅ . 4. Use according to claim 2 or 3, wherein R ² and R ^{3 are the} same. 5. Use according to claim 1, wherein as conductive salts LiPF ₆ , LißF ₄ , Li [N (SO ₂ CF ₃ ) ₂ ], Li [C (SO ₂ CF ₃ ) ₃ ] or LiSO ₃ CF ₃ are used. 6. Mixtures of conducting salts and compounds of the formula (I) in which R ¹ , R ² and R ^{3 have} the abovementioned meaning. 7. Mixtures according to claim 6, wherein the conductive salt is selected from the group comprising LiPF ₆ , LiBF ₄ , Li [N (SO ₂ CF ₃ ) ₂ ], Li [C (SO ₂ CF ₃ ) ₃ ] or LiSO ₃ CF. _3rd 8. Mixtures according to claim 6 or 7, with a content at least one other electrolyte solvent.