(The) kinetics of lithium transport through transition metal oxide film and composite electrodes

Abstract

The present work involves the kinetics of lithium transport through transition metal oxide film and composite electrodes. Chapter Ⅲ is concerned with lithium transport through $Li_{1-δ}CoO_2$ film and composite electrodes studied by analysis of current transient. The effect of cell-impedance on lithium intercalation/deintercalation has been investigated in Chapter Ⅲ-1. The typical current transient and change in lithium content profile across the electrode with time were presented by using numerical simulation based upon the two approaches: Conventional ``diffusion-controlled`` lithium transport through the electrode subjected to ``real potentiostatic`` constraint and the ``cell-impedance-controlled`` lithium transport across the electrode/electrolyte interface. Then, lithium transport through a carbon-dispersed $Li_{1-δ}CoO_2$ composite electrode was examined from the two points of view. From the comparison of experimentally obtained current transients with those numerically simulated, it is suggested that lithium transport during intercalation into and deintercalation from the $Li_{1-δ}CoO_2$ composite electrode in the single a phase region are purely governed by cell-impedance. However, the ``cell-impedance-controlled`` lithium transport during intercalation into the $Li_{1-δ}CoO_2$ electrode in the coexistence of two phases alpha and beta is converted into ``diffusion-controlled`` lithium transport. This transition in transport mechanism can be accounted for in terms of the input flux at the subsurface toward the electrode between by chemical diffusion and by the quotient of potential drop divided by cell-impedance. In Chapter Ⅲ-2, the contribution of the phase boundary between alpha phase and beta phase to lithium intercalation has been considered by using the numerical approach to the moving phase boundary problem. The derivatives of the second stages of the linear and logarithmic current transients in the coexistence of two phases were observed to b...