PERFORMANCES ELECTRIQUES ET ELECTROCHIMIQUES DE SMECTITES : APPLICATION AUX CAPTEURS ET AUX GENERATEURS ELECTROCHIMIQUES.

Abstract

This Work deals with the use of smectites (montmorillonite and nontronite) respectively as electrolyte and electrode materials for solid-state electrolyte batteries operating at room temperature. The protonic conductivity of montmorillonite was improved by increasing the concentration of mobile charge carriers (H+) and controlling its hydration level. This resulted in a high ionic conductivity which makes this material a potential candidate as a solid-state electrolyte for pH sensor and protonic batteries. Improvement of the performances of such systems goes through that of the other components, namely the anode and cathode materials. For the first, a Zn-based double-salt, simultaneously able to provide electrons to the external circuit, by oxidation of zinc at stable and durable negative potentials, and to exchange protons with the solid electrolyte (montmorillonite-H), was developed. For the cathode material, the use of a synthetic nontronite (an iron-rich smectite) was explored. The presence of Fe2+/Fe3+ redox couple, which ensures a positive potential, along with the layered structure of this smectite, which facilitates the bulk insertion of cations, fulfill the features required for an intercalation material. However, improvement of the low electronic conductivity of this material requires an additional effort in order to accelerate the kinetics of the insertion reaction. This was carried out by incorporation, between the layers of the clay, of an additive having good electronic conduction properties, such as polypyrrole. The process allowed the development of a nanocomposite with notably improved electric and electrochemical characteristics.