Safe extended-range cycling of Li4Ti5O12-based anodes for ultra-high capacity thin-film batteries

Lithium titanium oxide thin films are increasingly popular anode materials in microbatteries and hybrid supercapacitors, due to their improved safety, cost, and cycle lifetime. So far, research efforts have mainly focused on the pure spinel phase Li4Ti5O12 (LTO) and only a small fraction is dedicated to a broader spectrum of titanium-based metal oxide thin films. In this work, pulsed laser deposition is used in a multilayer approach by alternating LTO and Li2O ablations to create a heterogeneous landscape in the titania-based micro-anodes. This rich microstructure enables the safe extension of the accessible electrochemical window down to 0.2 V. This leads to extraordinary high specific capacities of 250–300 mAh/g at 1 C, maintaining a stable discharge capacity of 180 mAh/g at 16 C. Operando spectroscopic ellipsometry and Raman spectroscopy are used to track optical and structural changes as a function of the discharge voltage down to 0.01 V. A kinetically limited degradation mechanism based on the effective trapping of Li-ions at the octahedral 16c positions is proposed when cycling in the range of 0.2–0.01 V. In essence, our work contributes to titania-based nanoshapes as anodes of increased specific capacity due to a higher Li-site occupation, while maintaining their good stability and safety. [Display omitted] •Addition of lithium oxide to lithium titanate increases gravimetric capacity.•Electrochemical stability of the films is extended at low potentials.•Operando spectroscopic ellipsometry was performed to determine reversibility.