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