Chemistry: electrical current producing apparatus – product – and – Current producing cell – elements – subcombinations and... – Include electrolyte chemically specified and method
Reexamination Certificate
2000-04-28
2002-06-25
Chaney, Carol (Department: 1745)
Chemistry: electrical current producing apparatus, product, and
Current producing cell, elements, subcombinations and...
Include electrolyte chemically specified and method
C522S025000, C560S014000
Reexamination Certificate
active
06410190
ABSTRACT:
SUMMARY OF THE INVENTION
The invention relates to a process for the preparation of organic methanide electrolytes in useable quality for use in electrochemical cells.
The tris(perfluoroalkanesulfonyl)methanide class of compounds was described for the first time by Turowsky et al. in Inorgan. Chem., 1988, 27, 2135-2137 with reference to tris(trifluoromethanesulfonyl)methane. This C—H acidic compound reacts with bases to give the corresponding salts. The anion is planar, and the negative charge can be delocalized very well by the strongly electron-withdrawing substituents.
The lithium salt lithium tris(trifluoromethanesulfonyl)-methanide has been investigated for some time with respect to its suitability as conductive salt in secondary batteries owing to its high conductivity and good solubility in aprotic solvents. Further advantages of this salt are its high electrochemical and thermal stability.
There are two processes for the preparation of such compounds. According to Turowsky et al., tris[trifluoromethanesulfonyl]methane is prepared by a Grignard reaction with trifluoromethanesulfonyl fluoride.
A two-step process as described by Koshar et al. in J. Org. Chem., 1973, 38, 3358-3363, and Benrabah et al. in J. Chem. Soc. Faraday Trans., 1993, 89(2), 355-359, likewise gives tris[trifluoromethanesulfonyl]methane.
Both processes give products which require purification for use as conductive salt. Purification methods used hitherto, which are based on reaction of the solvated salt with activated carbon and recrystallization, give products having a purity of, in general, not greater than 99.5% which still contain interfering contamination by water and foreign ions.
However, salts of this quality are not suitable for use in organic electrolytes.
DETAILED DESCRIPTION
An object of the present invention is therefore to provide an inexpensive, easy-to-perform process by means of which organic methanide electrolytes are obtained in high-purity form, making the products prepared suitable for use in battery electrolytes. For the purposes of the invention, “high-purity” is taken to mean degrees of purity of greater than 99.5%, e.g. 99.6, 99.7, 99.8, 99.9%, or greater.
One object according to the invention is achieved by a process for the preparation of high-purity methanides of the formula
MC(SO
2
(C
x
F
2x+1
))
3
(I)
in which
x is 1, 2, 3, 4, 5, 6, 7 or 8, and
M is H, Li, Na, K, Rb, Cs, Mg
1/2
, Ca
1/2
, Sr
1/2
or Ba
1/2
, which are suitable as electrolytes, by purification, characterized in that it comprises the following steps:
(i) reaction of a methanide of the formula (I) with concentrated sulfuric acid, and fractional rectification of the resultant free acid of said methanide,
(ii) reaction of the product of the formula (I) in which M=H obtained from (i) with phosphorus pentoxide at or above the melting point followed by fractional rectification,
(iii) taking-up of the product of the formula (I) in which M=H from (ii) in an aprotic organic solvent, and reaction with metallic Li, Na, K, Rb, Cs, Mg, Ca, Sr or Ba, or chlorides or hydrides thereof, or with alkyllithium, to give the corresponding metal methanides of the formula (I), and, if necessary, removal of excess reagent.
The process according to the invention gives materials having a purity of greater than 99.5%, preferably from 99.6% to 99.9%, which are thus suitable for use as electrolytes in batteries.
Surprisingly, it has been found that the reaction with concentrated sulfuric acid stabilizes the starting material and thus enables it to be distilled without decomposition. In addition, the addition of equivalent amounts or an excess of concentrated sulfuric acid enables the free acid HC(SO
2
CF
3
)
3
to be obtained directly from its salts and purified.
The addition, in accordance with the invention, of highly hygroscopic sulfuric acid already achieves a good drying effect, which can be increased further by addition of sulfur trioxide, corresponding to the water content of the crude product.
It has also been found that the fractional rectification of the pure fraction with addition of phosphorus pentoxide gives a pure product having a water content of from 5 to 30 ppm, preferably from 10 to 20 ppm. This highly effective drying can be carried out economically on amounts of any desired size.
The use in accordance with the invention of a solvent which is used exclusively or proportionately in the finished electrolyte is particularly advantageous. This makes isolation of the salt, which is complex, unnecessary.
In the reaction in process step (iii), gaseous hydrogen, hydrogen chloride or alkanes form as easily removable by-products. In this reaction, it was noted that the neutralization of HC(SO
2
CF
3
)
3
in accordance with the invention prevents decomposition phenomena at the anion, as has been observed in conventional processes.
The reduction of the volume of the electrolyte by distillation in accordance with the invention has the significant advantage that the large excess of desired oxygen nucleophile present in the solution displaces undesired nucleophiles from the coordination sphere of the lithium. This effect allows impurities to be removed by distillation. A highly concentrated electrolyte is obtained, which enables low storage and transport costs.
It has been found that the dilution of the highly concentrated electrolytes can be carried out with any desired solvents. It is therefore possible, in a simple manner, to employ the optimum solvent mixture and to provide electrolytes in any desired concentration.
The purification essentially consists of 3 process steps, which can preferably be followed by two further steps.
Any conventional source of methanide is suitable for the purification, including, e.g. methanide produced by the process of Turowsky et al. or Koshar et al, cited above.
1st Step
A methanide of the formula (I) having a purity of from 90% to 99.5% is introduced in batches into concentrated sulfuric acid (96-98% sulfuric acid), and the mixture is stirred at temperatures of from 10 to 40° C. The mixture is preferably reacted with freshly distilled sulfuric acid at temperatures of from 20 to 30° C. The sulfuric acid is added in equivalent amounts or in excess. The rectification apparatus with isothermal column is baked out under a protective-gas atmosphere. The distillation bridge must be heatable by means of heating tapes or the like. This keeps the distillation bridge at a constant temperature above the respective melting point. Fractional rectification is carried out in this apparatus.
2nd Step
The pure fraction from step 1 is mixed with phosphorus pentoxide in a distillation apparatus which has been baked out under a protective-gas atmosphere. The mixture is stirred for from 15 minutes to 5 hours at temperatures at or above the melting point of the acid. The reaction is preferably carried out for from 30 minutes to 90 minutes. The mixture is subsequently subjected to fractional rectification under reduced pressure.
The fractional rectification of the pure fraction from step 1 with addition of phosphorus pentoxide gives a pure product having a water content of, preferably, from 10 to 30 ppm.
3rd Step
The product from step 2 is dissolved in polar organic solvents under a dry inert-gas atmosphere. Aprotic solvents, such as DMC, DEC, EC, PC, BC, VC, cyclopentanone, sulfolane, DMS, 3-methyl-1,3-oxazolidin-2-one, ?-butyrolactone, EMC, MPC, BMC, EPC, BEC, DPC, 1,2-diethoxymethane, THF, 2-methyltetrahydrofuran, 1,3-dioxolane, methyl acetate, ethyl acetate, and mixtures thereof, are particularly suitable. The solution is mixed with lithium hydride, with metallic lithium (Li), with lithium chloride, in situ using a lithium positive electrode, or with alkyllithium. In order to prepare the sodium, potassium, rubidium, cesium, magnesium, calcium, strontium or barium compounds, a reaction can be carried out with metallic sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), calcium (Ca), strontium (Sr) or barium (Ba), sodium chloride, potassium ch
Barthen Peter
Ignatiev Nikolai
Sartori Peter
Chaney Carol
Merck Patent Gesellschaft mit beschraenkter Haftung
Millen White Zelano & Branigan P.C.
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