A study on lithium transport through fractal Li1-delta CoO2 film electrode by analysis of current transient based upon fractal theory

Abstract

Lithium transport through fractal Li1-deltaCoO2 film electrode was investigated in a 1 M lithium perchlorate (LiClO4)-propylene carbonate (PC) solution by analysis of current transient based upon fractal theory. For this purpose, two kinds of Li1-deltaCoO2 films were deposited by rf magnetron sputtering method on the substrates with different roughnesses. From the analysis of AFM image by the triangulation method, it was found that two Li1-deltaCoO2 film electrodes have the self-similar scaling properties with different spatial outer cut-off ranges. From the analysis of the potentiostatic current transient, it was recognised that the cell-impedance-controlled constraint at the electrode surface is changed to the real potentiostatic boundary condition (diffusion-controlled constraint) when the applied potential step exceeds a critical value and simultaneously the internal cell resistance is below a certain value in the region of single-beta-phase. In addition, from the comparison between the cathodic current transients obtained from two fractal Li1-deltaCoO2 film electrodes, it was experimentally confirmed that the current transient shows the generalised Cottrell behaviour before the temporal outer cut-off of fractality, followed by a linear relationship with the slope of -0.5 after the temporal outer cut-off of fractality, when the real potentiostatic boundary condition is maintained at the electrode Surface. (C) 2004 Elsevier Ltd. All rights reserved.