Cell-impedance-controlled lithium transport through Li1-delta Mn2O4 with Fractal surface by analyses of experimental PCT and LSV

Abstract

Lithium transport through the fractal Li1-delta Mn2O4 film electrode with partially inactive surface under the cell-impedance-controlled constraint was investigated by employing ac-impedance spectroscopy, potentiostatic current transient (PCT) technique and linear sweep voltammetry (LSV). For this purpose, the totally active and partially inactive Li1-delta Mn2O4 film electrodes were obtained by surface modification of Li1-delta Mn2O4 film with polyvinylidene fluoride (PVDF) binder. Based upon the perimeter-area relation, the fractal dimension dF of the partially inactive surface was determined. From the analysis of the ac-impedance spectra obtained from the totally active and partially inactive fractal electrodes, it was found that the charge-transfer kinetics strongly depends upon the surface coverage by active sites theta. All the potentiostatic current transients did not exhibit the generalized Cottrell behavior even before the characteristic time t(ch) and all the power dependence of the peak current on the potential scan rate deviated from the generalized Randles-Sevcik behavior even above the characteristic scan rate v(ch) in the linear sweep voltammograms. In particular, as either theta or d(F) falls in value, the value of t(ch) is prolonged and at the same time the value of v(ch) is reduced as well. From the analyses of the potentiostatic current transients and the linear sweep voltammograms in terms of t(ch) and v(ch), it was experimentally confirmed that the partial inactivity of the surface plays a significant role in the interfacial charge-transfer reaction and subsequent diffusion reaction during the whole lithium intercalation and deintercalation processes. (c) 2007 The Electrochemical Society.