Comparison of Amorphous TiO2 with Anatase Thin-Films Grown By ALD in Terms of Rate Performance and Capacity for Li+-Insertion

Monday, 27 July 2015
Hall 2 (Scottish Exhibition and Conference Centre)
S. Moitzheim (imec, KU Leuven), S. Deng, C. Detavernier (Ghent University), S. De Gendt (imec vzw), and P. M. Vereecken (KU Leuven)
In this work we compare amorphous TiO2 to anatase thin-films for their Li+ insertion/extraction properties. For this, we deposited ultra-thin (35 nm) amorphous TiOand anatase films by atomic layer deposition on a TiN current collector. Such thin films are interesting since they have the same length scale as nanostructured particles or other nanostructures, e.g. nanotubes, but with the additional benefit of offering a well-defined geometry that allows for a more precise determination of the underlying lithium insertion/extraction kinetics. Furthermore, such ultra-thin electrodes might find application in 3D (micro-)batteries.

The amorphous and anatase films were characterized using cyclic voltammetry and galvanostatic charging/discharging. The electrochemical properties of 35 nm amorphous TiO2 and anatase films are shown in figure 1. The cyclic voltammograms (CV, see figure 1a) performed at 10 mV/s shows distinction between lithium insertion/extraction of the amorphous and anatase films. The average of the insertion and extraction peak potentials is 1.65 V vs Li+/Li and 1.99 V vs Li+/Li for amorphous and anatase, respectively.  Also, the peaks in the CV for amorphous TiO2 are less sharp compared to anatase, suggesting a different intercalation mechanism.

Galvanostatic charge/discharge experiments show a significantly increased capacity for amorphous compared to anatase (see figure 1b). At 1C, the amorphous TiO2 film has a capacity of 1.9 µAh/cm2 compared to 1.2 µAh/cm2 for the anatase film. Also, at higher C-rates the amorphous TiO2 film shows high retention of the capacity. For example, at 20C, 63% of the capacity at 1C is retained, compared to 30% for anatase. These results show the potential benefits of using amorphous TiO2 compared to anatase thin-films due to its significantly higher capacity and superior rate performance.