Lithium intercalation into titanium dioxide: investigation by electrochemical and photoelectrochemical methods

The electrochemical intercalation of lithium from propylene carbonate solutions into thin film Ti02 electrodes prepared by the heat treatment of Ti support was studied. Photoelectrochemical characteristics of film electrodes were investigated at potentials E corresponding to active insertion/extraction of lithium (1.0 < Е < 2.5 В vs Li/Li+) and inert regions. Equivalent circuit which satisfactorily models impedance spectrum of TiO2- and LixTiO2-electrodes in investigated frequency range from 103 to 10'2 Hz is suggested. Electrochemical characteristics of film electrodes, influence of surface passivation on the lithium transport rate, dependencies of electrical, kinetic, diffusion and photoelectrochemical parameters on potential (composition) of electrode are discussed. Diffusion coefficients of lithium into LixTiO2 (~10-12 cm/s) were determined. Sharp change of equivalent circuit parameters and also disappearance of anodic current and appearance of weak cathodic current correlates with the beginning of active lithium insertion into the initial oxide.