H. Lindstrom et al., LI+ ION INSERTION IN TIO2 (ANATASE) .2. VOLTAMMETRY ON NANOPOROUS FILMS, JOURNAL OF PHYSICAL CHEMISTRY B, 101(39), 1997, pp. 7717-7722
Electrochemical properties of Li+ ion insertion in nanoporous TiO2 (an
atase) electrodes were studied by voltammetry. Linear and cyclic poten
tial scans were recorded as a function of electrolyte concentration, f
ilm thickness, and temperature. The currents were directly proportiona
l to the inner electrode area of the electrodes. The reduction of Ti4 and oxidation of Ti3+ are sluggish and follows irreversible kinetics.
The standard rate constant was (3.5 +/- 0.5) x 10(-10) cm/s. The tran
sfer coefficient was close to 0.5, indicating that the potential drop
appears mainly across the Helmholtz layer. The capacitive currents gov
ern largely the shape of the i-v curves, except within a region near t
he peak potential where diffusion-limited insertion and extraction of
Li+ ions in the anatase lattice are dominating. The diffusion coeffici
ent at 25 degrees C in the nanoporous structure was approximately 2 x
10(-17) cm(2)/s for insertion and 4 x 10(-17) cm(2)/s for extraction.
The activation energy was 0.4 eV for insertion and 0.5 eV for extracti
on. The maximum obtained mole fraction of Li+ in LixTiO2 was x = 0.47.