Materials useful as electrolytic solutes

Details Materials useful as electrolytic solutes Materials useful as electrolytic solutes

1999-09-07

2002-04-02

Kalafut, Stephen (Department: 1745)

Chemistry: electrical current producing apparatus, product, and

Current producing cell, elements, subcombinations and...

Include electrolyte chemically specified and method

C429S315000, C429S324000, C359S270000, C423S301000, C423S302000, C423S307000, C423S386000, C423S387000, C568S009000, C568S011000, C568S036000, C568S557000, C570S141000, C570S142000

Reexamination Certificate

active

06365301

ABSTRACT:

FIELD OF INVENTION
The present invention relates to ionic compositions having a high ionic conductivity, comprising a salt wherein the anionic charge is delocalized, and their uses, such as an electrolyte.
BACKGROUND OF THE INVENTION
Room temperature molten salts, such as triethyl ammonium nitrate, have been known for a long time. This product is of no interest except because of the presence of a leaving proton on the cation, limiting the redux or acido-basic stability domain of the compound. Methyl-ethylimidazolium or butyl-pyridinium type compounds, associated to the complex ion [Cl
−
, xAlCl
3
] wherein 1<x<2, are also known. These compounds, because of the presence of the aluminium chloride, are powerful Lewis acids, hygroscopic and corrosive because they generate hydrochloric acid in the presence of humidity. Their electrochemical stability domain is also limited by the anodic oxydation of the chloride ion on one side, and by the reduction of the aluminium ion on the other side.
The use of anions usually stables associated to imidazolium or pyridinium type cations has been proposed, but the melting points are relatively high. For example, 1-methyl-3-ethylimidazolium hexafluorophosphate melts at 60° C., and 1,2-dimenthyl-3-propylimidazolium hexafluorophosphate melts at 65° C. In addition, these salts, although not hygroscopic, are nevertheless soluble in water and can therefore be hardly prepared by ion exchange in water unless longer alkyl substituents are used, which results in a strong reduction in conductivity and enhanced viscosity.
U.S. Pat. No. 5,827,602 describes salts with a melting point relatively low, with a selection criteria being an anion volume higher than 100 Å
3
, thus allowing to obtain salts with high conductivity and hydrophobic character. Most representative anions are the bis-trifluoromethanesulfonimidide, that has a calculated volume of 144 Å
3
with Hyperchem® program, or the tris-trifluoromethanesulfonylmethylide, which has a volume of 206 Å
3
.
SUMMARY OF THE INVENTION
The present invention is concerned with low melting point ionic compounds, preferably lower than room temperature, wherein the cation is of the onium type and having at least one heteroatom such as N, O, S or P bearing the positive charge and is wherein the anion comprises, in whole or in part, at least one imidide ion of the type (FX
1
O)N
−
(OX
2
F) wherein X
1
and X
2
are the same or different and comprise SO or PF. More specifically, the onium type cation comprises a compound of formula:
a compound of formula
a compound of formula
a compound of formula
wherein
W is O, S or N, and wherein N is optionally substituted with R
1
when the valence allows it;
R
1
, R
3
, R
4
are the same or different and represent
H;
an alkyl, alkenyl, oxaalkyl, oxaalkenyl, azaalkyl, azaalkenyl, thiaalkyl, thiaalkenyl, dialkylazo, each of these can be either linear, branched or cyclic and comprising from 1 to 18 carbon atoms;
cyclic or heterocyclic aliphatic radicals of from 4 to 26 carbon atoms optionally comprising at least one lateral chain comprising one or more heteroatoms;
groups comprising several aromatic or heterocyclic nuclei, condensed or not, optionally comprising one or more atoms of nitrogen, oxygen, sulfur or phosphorous; and wherein two groups R
1
, R
3
or R
4
can form a cycle or a heterocycle of from 4 to 9 carbon atoms, and wherein one or more R
1
, R
3
or R
4
groups on the same cation can be part of a polymeric chain;
R
2
and R
5
to R
9
are the same or different and represent R
1
, R
1
O—, (R
1
)
2
N—, R
1
S—, R
1
being as defined above.
The invention further comprises an electrolytic composition comprising at least one ionic compound as defined above in combination with at least another component comprising a metallic salt, a polar polymer and/or an aprotic co-solvent.
DETAILED DESCRIPTION OF THE INVENTION
It has been found that onium-type cation salts as defined above, and preferably the imidazolium, ammonium, sulfonium and phosphonium salts, associated to anions of the family represented by the general formula (FX
1
O)N
−
(OX
2
F) as defined above allow to obtain liquid salts at temperatures equal or lower than those obtained with larger ions. Further, their conductivity is, in all instances, at the same temperature, superior to that of the compounds described in U.S. Pat. No. 5,827,602. These liquid salts are hydrophobic even though the anion size is small, comprised between 85 and 92 Å
3
, and thus, easily prepared by ion exchange in water, and can be handled without any particular precaution. Unexpectedly, these salts show an oxydation stability equal to that of the bis(trifuoromethanesulfonimidide) or tris(trifluoromethanesulfonyl)methylide anions, and higher than that obtained with anions of the tetrafluoroborate or hexafluorophoborate type.
The compounds of the present invention can, in addition to the imidide anion mentioned above, comprise at least another anion selected from Cl
−
; Br
−
; I
−
; NO
3
−
; M(R
10
)
4
−
A(R
10
)
6
−
; R
11
O
2
−
, [R
11
ONZ
1
]
−
, [R
11
YOCZ
2
Z
3
]
−
, 4,5-dicyano-1,2,3-triazole, 3,5-bis(R
F
)-1,2,4-triazole, tricyanomethane, pentacyanocyclopentadiene, pentakis-(trifluoromethyl)cyclopentadiene, barbituric acid and Meldrum acid derivatives and their substitution products;
M is B, Al, Ga or Bi;
A is P, As and Sb;
R
10
is a halogen;
R
11
represents H, F, alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl, dialkylamino, alkoxy or thioalkoxy, each having from 1 to 18 carbon atoms and being unsubstituted or substituted with one or more oxa, thia, or aza substituents, and wherein one or more hydrogen atoms are optionally replaced with halogen in a ratio of 0 to 100%, and eventually being part of polymeric chain;
Y represents C, SO, S═NCN, S═C(CN)
2
, POR
11
, P(NCN)R
11
, P(C(CN)
2
R
11
, an alkyl, alkenyl, aryl, arylalkyl, alkylaryl, arylalkenyl, alkenylaryl having from 1 to 18 carbon atoms and optionally substituted by one or more oxa, thia or aza; a dialkylamino group N(R
10
)
2
;
Z
1
to Z
3
representing independently R
11
, R
11
YO or CN, this group being optionally part of a polymeric chain.
Another advantage of the compounds of the invention is the low cost of the starting anions, their preparation not requiring perfluoroalkyl chemistry such as CF
3
or C
4
F
9
for instance, the fluorine atoms present in the compounds of the invention being derived from inorganic chemistry products, thus easily accessible. This economical aspect is particularly important because the molten salts contain between 40 and 75% by weight of the anionic species, the remainder being the cationic species. In addition, the density of these liquids is close to 1.5, compared to about 1 for the organic solutions, which requires more important quantities of salts for all applications wherein a volume or a given thickness are necessary, such as electrolyte films, chemical reactors, etc.
Another particularly important aspect of the present invention is the possibility for these molten salts to dissolve other salts, in particular metallic salts, such as lithium salts, to give highly conductive solutions. In a similar manner, the molten salts, or their mixtures with other metallic salts, are excellent solvents or plasticizers for a great number of polymers, in particular those bearing polar or ionic functions. Liquid compounds as well as polymers plasticized by ionic mixtures behaving like solid electrolytes are applicable in electrochemistry to generators of the primary or secondary type, supercapacities, electrochromic systems, antistatic coatings, or electroluminescent diodes. The non-volatility of the molten salts of the invention, their thermal and electrochemical stability, and their enhanced conductivity are important parameters for the fabrication of devices working at low temperature and not presenting the usual flammability risks associated with the use of conventional organic solvents.

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