Materials for electrodes: Amorphous and thin-films

Abstract

Until now, the materials investigated with a view to finding suitable intercalation host structures for the positive electrode of electrochemical generators with an alkali metal or silver anode have been essentially crystalline (transition metal didialcogenides and oxides). Yet the discovery of the semiconducting properties of phosphorus pentoxide-based glasses, a quarter of a century ago [1], associated with the synthesis of phosphate-based glasses with high ionic conductivity [2–3] allows us to consider the possibility of employing glasses as positive electrode materials. These materials could offer significant technological advantages due to their vitreous structure:

• 1. Easy to synthesize;

• 2. Easy to implement, in particular in the form of micronic powders;

• 3. Isotropic structure, implying a larger electrochemically active surface than in the case of low dimensionality crystalline structures;

• 4. The good conductivities observed in glasses suggest a high diffusion coefficient of the mobile ion;

• 5. The low density of glasses infers a large number of available sites for the intercalants and, consequently, independence of the volume of the material with respect to the intercalation ratio. The use of glasses for the positive electrode of solid state secondary batteries should ensure that good contacts are maintained throughout the discharge-charge cycles;

• 6. The use of the same forming oxide in the electrolyte and the electrode should avoid a clear-cut localization of their interface since the macromolecular chains of the forming oxide will extend without interruption from the electrolyte to the electrode.