[en] Mesoporous thin films are promising architectures for positive electrodes in Li-ion battery applications. A particular challenge in this field has been successful templating of vanadium-based oxides, materials known for their ability to host lithium, since their thermal instability and complex vanadium chemistry hinder templating through traditional soft-chemistry approaches. To address these technical problems we develop the soft-templating of vanadium and niobium mixed oxides based on Evaporation Induced Micelles Packing using thermally stable polystyrene-b-polyethyleneoxide structuring agents. In-situ thermal monitoring via ellipsometry allows successful navigation of the thermal stability landscape. TEM and AFM analyses reveal homogeneous wormlike mesoporous structures whose pore and inorganic wall sizes can be tuned from 15 to 100 nm by changing the hydrophobic/hydrophilic surfactant chain lengths. Ellipsometric porosimetry shows that 100 nm thick films with a 15 nm pore size displays 30% electrolyte accessible porosity. The interconnected tridimensional mesoporous network has been highlighted by electronic tomography. Thicker films up to 1.3 µm are prepared by a multidipping process. The superiority of such nanoarchitectures compared to non porous materials in terms of electrochemical properties such as capacity are revealed using cyclic voltammetry.
Laboratoire de Chimie Inorganique et Structurale
Fonds de la Recherche Scientifique (Communauté française de Belgique) - F.R.S.-FNRS ; Mandat d'assistanat à l'Université de Liège
Synthèse de nouveaux matériaux d'électrodes positives pour les accumulateurs au lithium