Superior Electrochemical Performance of Amorphous Titanium Niobium Oxide Thin Films for Li-Ion Thin Film Batteries

Abstract

Titanium niobium oxide (TiNb2O7, TNO) has emerged as a competitor for Li4Ti5O12 (LTO) anode material for the next-generation high energy solid-state batteries. However, the usage of TNO is mainly limited by its low electronic conductivity and low lithium-ion diffusivity, which need to be improved for efficient electrochemical kinetics. Amorphous energy storage materials have been widely considered as alternatives. Here, we report the fabrication of amorphous TNO thin films and their electrochemical performance in half-cell rechargeable Li-ion thin film batteries. The amorphous TNO thin films exhibit: a high discharging capacity of 226 μAh/μm cm2 (∼460 mAh/g) at 17 μA/cm2 current density, the high coulombic efficiency of ∼99%, fast kinetics and stable structure. The amorphous TNO thin films further show a high discharge capacity than amorphous LTO thin films, which is twice greater than crystalline TNO thin films. They offer Li-ion diffusion coefficient of ≈10−13 cm2/s, better electron-transfer reaction and high electronic conductivity (≈1 × 10−9 S/cm) during electrochemical cycling process. The superior electrochemical performance of amorphous TNO thin films are attributed due to their unique disordered structure and morphology features.