Lithium transport through Li1+delta[Ti2-yLiy]O-4 (y = 0; 1/3) electrodes in the coexistence of a Li-poor phase alpha and a Li-rich phase beta was investigated during electrochemical lithium intercalation by using the potentiostatic current transient technique under large potential stepping. For this purpose, the galvanostatic charge-discharge curve and the cathodic current transient were obtained as functions of the lithium content (1 + delta) and the lithium injection potential, respectively. The charge-discharge curve showed a potential plateau due to the coexistence of two phases alpha and beta. The values of the quasi-equilibrium potential and the corresponding stoichiometry of the alpha- and beta-phases were determined from the potential plateau. A three-stage current transient was observed as the applied potential step went below the potential plateau, and the second stage of this current was found to be governed by the diffusion-controlled phase boundary movement between the alpha- and beta-phases.