Lithium transport through a sol-gel derived LiMn2O4 film electrode:: analyses of potentiostatic current transient and linear sweep voltammogram by Monte Carlo simulation

Lithium transport through a sol-gel derived LiMn2O4 film electrode was theoretically investigated by analyses of the potentiostatic current transient and the linear sweep voltammogram in consideration of the interactions between lithium ions by using Monte Carlo simulation. The anodic current transients experimentally measured on the film electrode ran with the slope of logarithmic current with logarithmic time flatter than -0.5 in the early stage, and then did in an upward concave shape in the time interval between t(T1) and t(T2). The linear sweep voltammograms experimentally measured on the film electrode showed two anodic peak currents I-p1 and I-p2 which increased linearly with scan rate v to the power of 0.66 and 0.70, respectively, (i.e. I(p1)proportional to (upsilon)0.66 and I-p2 proportional to upsilon(0.70)) at the scan rates higher than 0.5 mV s(-1). Moreover, the higher v was, the larger appeared the positive deviations of the first and second peak potentials E-p1 and E-p2 from the first and the second transition potentials E-p1(o), and E-p2(o), respectively, in the inverse derivative of the electrode potential curve. The current transients and the linear sweep voltammograms were analyzed in consideration of the interactions between lithium ions in the electrode by using the Monte Carlo Simulation under two different constraints of the diffusion-controlled lithium transport and the cell-impedance-controlled lithium transport. The current transients and the linear sweep voltammograms, theoretically calculated under the cell-impedance-controlled constraint in consideration of the interactions between lithium ions, were in good agreement with the experimental results in shape. The disorder to order phase transition in the LiMn2O4 film electrode during the cell-impedance-controlled lithium transport at the potential jump and scan was discussed with the aid of the concentration profiles and the local cross-sectional snapshots of the configuration of lithium ions simulated by the Monte Carlo method. (C) 2002 Elsevier Science Ltd. All rights reserved.