Chemistry: electrical current producing apparatus – product – and – Having specified venting – feeding or circulation structure – Having electrolyte storage feeding a device
Patent
1992-03-16
1993-07-13
Liederman, Paul
Chemistry: electrical current producing apparatus, product, and
Having specified venting, feeding or circulation structure
Having electrolyte storage feeding a device
252518, 252521, 429 33, 429 46, 429188, 429191, 429193, H01M 800
Patent
active
052272575
DESCRIPTION:
BRIEF SUMMARY
The object of the invention is novel compositions derived from Bi.sub.4 V.sub.2 O.sub.11 and their electrochemical applications, in particular as electrolytes which conduct by means of O.sup.2- (oxide) anions.
A solid electrolyte conducting by means of O.sup.2- anions is a material in which the O.sup.2- anions or the vacancies can move in a coordinated manner under the effect of an external stress such as an electric field or a partial pressure difference of oxygen.
The materials currently available are essentially derivatives of zirconium oxide ZrO.sub.2, stabilized by divalent oxides such as CaO or by trivalent oxides such as Y.sub.2 O.sub.3 (R. M. Dell et al., Solid electrolytes, ed. by P. Hagenmuller and W. Van Gool, Academic Press) or, better still, derivatives of Bi.sub.2 O.sub.3 stabilized mainly by oxides of rare earth metals such as Er.sub.2 O.sub.3 (M. J. Verkerk et al., Journal of Applied Electrochemistry 10 (1980) 81-90,
These latter have conductivities of the order of 10.sup.-1 .OMEGA. cm.sup.-1 at 600.degree. C., but their performance falls off rapidly with temperature (see FIG. 1).
The stabilized ZrO.sub.2 and Bi.sub.2 O.sub.3 oxides possess the same basic structure, derived from the so-called fluorite structural type, in which the O.sup.2- sites exhibit vacancies which allow the movement of anions, which is hence a three-dimensional structure.
A high conductivity, even higher than 10.sup.-1 .OMEGA..sup.-1 cm.sup.-1, has been observed in the gamma phase of Bi.sub.4 V.sub.22 O.sub.11, above about 550.degree. C. (see FIG. 1).
This compound possesses three structural domains, alpha, beta and gamma. The structural changes which occur during the phase transitions on cooling cause falls in the conductivity during the transformations gamma.fwdarw.beta, followed by beta.fwdarw.alpha.
The gamma phase in Bi.sub.4 V.sub.2 O.sub.11 is characterized by a series of layers of Bi.sub.2 O.sub.2.sup.+, alternating with lamellae of formula VO.sub.3.5.sup.2-
The Bi.sub.2 O.sub.2.sup.2+ layers are constituted of oxygen atoms arranged in the same plane at the corners of adjacent squares, the bismuth atoms being situated alternately above and below these squares. Between two Bi.sub.2 O.sub.2.sup.2+ layers a lamella constituted by the oxygenated polyedra of vanadium is intercalated, linked through apices and extending in a plane parallel to that of the Bi.sub.2 O.sub.2.sup.2+ ; these lamellae contain vacancies for oxygen. The inventors have now observed that by partially substituting at least one of the constitutive elements of Bi.sub.4 V.sub.2 O.sub.11, it is possible to stabilize the gamma phase chemically.
The object of the invention is thus to provide novel compositions derived from Bi.sub.4 V.sub.2 O.sub.11, which have an improved conductivity compared with that of the known oxides used hitherto as electrolytes.
It also relates to the provision of an easily implementable process for their production.
The invention also relates to taking advantage of the high conductivity properties of the novel compositions derived from Bi.sub.4 V.sub.2 O.sub.11 for the development of electrolytes which depend on conduction by O.sup.2- ions.
The compositions of the invention are derivatives of Bi.sub.4 V.sub.2 O.sub.11 in which at least one of the constitutive elements is partially replaced, the substituting element(s) being such that the structural type of the gamma phase of Bi.sub.4 V.sub.2 O.sub.11 is maintained as well as is the balance of the charges.
The compositions of the invention are more particularly characterized in that they correspond to the formula (I): having an oxidation number lower than or equal to 3, having an oxidation number lower or equal to or higher than 5, the limiting values of x, y and hence z being functions of the nature of the replacement elements M and M'.
The partial replacement of the constitutive elements of Bi.sub.4 V.sub.2 O.sub.11 as defined above stabilizes the structural type of the gamma phase and maintains a proportion of vacancies in the O.sup.2- ion network sufficient to make possibl
REFERENCES:
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Abraham Francis
Boivin Jean-Claude
Fouletier Jacques
Kleitz Michel
Mairesse Gaetan
Kopec M.
Liederman Paul
Universite des Sciences et Techniques de Lille Flandres Artois E
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