Proton conductors in liquid form

Details Proton conductors in liquid form Proton conductors in liquid form

1998-08-28

2000-09-19

Epps, Georgia

Compositions

Electrolytes for electrical devices

359265, 359270, H01B 112, B02F 115

Patent

active

061206962

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The present invention relates to novel proton conductors in liquid form and to their use as liquid, gel or polymer electrolytes in various electrochemical systems.


BACKGROUND OF THE INVENTION

The most common proton conductors are obtained by doping water with an acid such as HCl or H.sub.2 SO.sub.4, or a base such as KOH or NH.sub.3. Thus, aqueous solutions of sulfuric acid have a high proton conductivity greater than 10.sup.-2 S.multidot.cm.sup.-1 and solutions of potassium hydroxide which are also very conducting are widely used as electrolytes in Nickel-Cadmium.
Proton conductors requiring the presence of water in order to function generally have a field of use limited in temperature due to the evaporation of the water and a field of redox stability limited to that of water. The presence of water also usually induces corrosion phenomena within the systems utilizing these electrolytes.
In order to overcome these redhibitory problems with respect to certain applications, a number of works have born on the study of anhydrous proton conductors. From the various classes of materials resulting from these researches, there have been more particularly obtained anhydrous proton conductors by substituting the aqueous solvent with non-hydroxylic solvating polymers such as polyethylene oxide, polyvinylpyrrolidone, polyethyleneimine or polyaminopropylsiloxane.
By doping these polymers with acids or bases, one obtains anhydrous proton conductors. For examples, dissolving orthophosphoric acid H.sub.3 PO.sub.4 in polyethylene oxide (POE) enables one to obtain an acidic proton conductor, and dissolving sulfonamide H.sub.2 NSO.sub.2 NH.sub.2 in the same polymer enables one to obtain a basic proton conductor.
These electrolytes are useful for making electrochemical systems, particularly light-modulating systems, but they still have major drawbacks. Proton conductors obtained by dissolving H.sub.3 PO.sub.4 in POE are corrosive due to the high acidity of the medium (pK.sub.a .apprxeq.0). On the contrary, the high basicity (pK.sub.a .apprxeq.11-12) of proton conductors obtained by dissolving sulfonamides in POE limits their uses. Indeed, in the presence of many electrode materials containing metallic species, there is formed a passivation layer which is a poor conductor of metallic cations complexed with sulfamide. On the other hand, these electrolytes are poor conductors at low temperature.


SUMMARY OF THE INVENTION

In order to overcome the above drawbacks, the inventors have found quite surprisingly that binary mixtures of certain nitrogen bases belonging to the azole family with appropriate acid addition salt of these nitrogen bases form proton conductors having a melting point lower than room temperature, a weak vapor tension and a conductivity similar to that obtained in aqueous medium.
According to the present invention, there is thus provided a proton conductor in liquid form, comprising a mixture of the following components (a) and (b): ##STR3## wherein: Z.sub.1, Z.sub.2, Z.sub.3 et Z.sub.4, identical or different, each represent a group --N.dbd. or --C(Y.sub.i).dbd. in which Y.sub.i represents a hydrogen atom, a linear or branched alkyl group having 1 to 20 carbon atoms, a fluoroalkyl radical having 1 to 20 carbon atoms, or an oxoalkyl or azaalkyl radical having 1 to 20 carbon atoms, with the proviso that at least one and at most two of the groups Z.sub.1, Z.sub.2, Z.sub.3 et Z.sub.4 represents --N.dbd., two adjacent carbon atoms being optionally hydrogenated and the nitrogen base optionally being part of a polymeric network, and consisting of sulfonic acids of formula R.sub.F SO.sub.3 H, sulfonamides of formula (R.sub.F SO.sub.2) (R'.sub.F SO.sub.2)NH and methylides of formula (R.sub.F SO.sub.2) (R'.sub.F SO.sub.2)CH.sub.2 or (R.sub.F SO.sub.2) (R'.sub.F SO.sub.2) (R".sub.F SO.sub.2) CH, in which R.sub.F, R".sub.F and R".sub.F each represents a radical F(CF.sub.2).sub.n --, n being comprised between 0 and 6, the acid optionally being part of a polymeric network; and ##STR4## in which Z.

REFERENCES:
patent: 5688613 (1997-11-01), Li et al.
patent: 5795496 (1998-08-01), Yen et al.

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