Electrostatic rectification of Li+ transport in amorphous TiO <i>x</i> thin films grown by mist CVD

Abstract

Amorphous metal oxide interlayers are widely used to stabilize Li+ transport at battery interfaces, yet the underlying transport mechanisms remain unclear. Here, Li+ transport in amorphous TiOx (a-TiOx) thin films prepared by mist chemical vapor deposition was investigated by comparing electrochemical lithiation with concentration-driven Li+ insertion induced by LiPF6 exposure. Electrochemical lithiation enables redox-assisted, dynamically activated Li+ diffusion accompanied by partial Ti4+ reduction, whereas LiPF6 exposure results in diffusion-limited Li+ transport without significant electronic reduction. Depth-resolved glow discharge optical emission spectroscopy and spectroscopic ellipsometry clearly distinguish these two regimes. In addition, dielectric contrast between the electrolyte, a-TiOx, and graphite is proposed to generate internal electric fields that directionally bias Li+ transport. A Drude-like sub-gap optical response originates from field-induced polarization and localized electronic states rather than metallic conduction. These results highlight the importance of dielectric-field effects in amorphous oxide interlayers for improving interfacial stability and rate performance in lithium-based batteries.