WO3 thin films by spray-coating as high voltage anode material for all-solid-state Li-ion batteries

Abstract

Lithium-ion (Li-ion) batteries are promising candidates to tackle the challenging energy storage problem due to their high power and energy density. However, contemporary Li-ion batteries could be improved significantly by introduction of a solid electrolyte. Many of these electrolytes contain titanium (e.g. Li0.35La0.55TiO3 and Li1.3Al0.3Ti1.7(PO4)3), limiting their electrochemical stability to 1.5V, due to Ti(IV) reduction. High voltage anode materials are therefore interesting candidates to fabricate an all-solid-state Li-ion battery. In the presented study, WO3 films are investigated as a potential high voltage anode material for Li-ion batteries. Films were prepared by spray-coating a precursor solution of tungsten chloride, dissolved in an ethanol-water mixture, on Pt and TiN coated Si. Thermal analysis was done to study the decomposition and optimize the deposition of the precursor. Phase pure monoclinic and triclinic films were obtained on TiN and Pt coated Si, respectively. Depending on the spray deposition temperature, smooth films were obtained with a thickness of 150 nm. Electrochemical activity of the films was proven by cyclic voltammetry from annealing temperatures of 400°C and up. The triclinic phase obtained on Pt coated Si substrates yielded the most promising electrochemical performance. The results of the current study gives important insight in the precursor deposition behaviour and phase formation of WO3 films for all-solid-state Li-ion batteries.