Ultrasonic spray deposited WO3 thin films as high voltage anodes 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 ultrasonic spray deposition of a precursor solution of tungsten chloride, dissolved in an ethanol-water mixture, on TiN and Pt coated Si. Thermal analysis and mass spectroscopy aided methods (TGMS, GCMS) were applied to study the precursor chemistry and to optimize the deposition of the precursor. Phase pure tetragonal films were obtained on TiN coated Si, whereas Pt coated Si yielded a blend of cubic and tetragonal WO3. 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 tetragonal phase obtained on TiN coated Si substrates yielded the most promising electrochemical performance, as charge-discharge measurements indicated a capacity of 95 mAh/g. The results of the current study provide important insights in the precursor deposition behaviour and phase formation of WO3 films for all-solid-state Li-ion batteries.