Lithium Transport through Porous Li1-δCoO2 Electrode: Analysis of Current Transient

Abstract

Lithium transport through a porous Li1-deltaCoO2 electrode was investigated during lithium intercalation and deintercalation using the current transient technique. The measured current transients following large potential steps were analysed in terms of the movement of the alpha/beta phase boundary based upon the concept of the quasi-equilibrium potential and the corresponding lithium stoichiometry established by transient measurements of open-circuit potential. From the value of (D) over tilde(Li+), beta smaller than (D) over tilde(Li+), alpha determined by electrochemical impedance spectroscopy, it was theoretically derived that just after being established, the alpha/beta phase boundary is pinned by the inner alpha-phase during a period of lithium intercalation until the concentration gradient across the alpha-phase developed during the build-up of the phase boundary nearly vanishes. This pinning was readily substantiated experimentally by the comparison of the current build-up and decay transients in response to small potential steps. From the appearance of such transients, it was inferred that lithium transport through the oxide electrode is mainly enhanced by the lithium ion diffusivity term during lithium intercalation, but it is mainly impeded by the electric field term during lithium deintercalation. (C) 1998 Elsevier Science Ltd. All rights reserved.