The kinetics of lithium transport through a composite electrode made of mesocarbon-microbeads heat-treated at 800 °C investigated by current transient analysis

Abstract

Lithium transport through a mesocarbon-microbeads composite electrode was investigated in a 1 M LiPF6 solution in ethylene carbonate/diethyl carbonate (1:1 by vol%) using a galvanostatic intermittent titration technique and a potentiostatic current transient technique. From analysis of the anodic current transient it is recognized that when the potential step is small enough for the lithium extraction potential to be below the transition potential, the lithium concentration is not fixed at the electrode surface, but the change in surface concentration with time is determined by the "cell-impedance-controlled" boundary condition. In contrast, when the potential step is large enough for the lithium extraction potential to be above the transition potential, the "real potentiostatic" boundary condition is then established at the electrode surface. Moreover, a "quasi-current plateau" was observed in a certain anodic current transient. This experimental result was theoretically analysed, based upon the modified McNabb-Foster equation as a governing equation. This strongly indicates that the difference in activation energies for lithium deintercalation between the different lithium deintercalation sites existing within the electrode accounts for the different kinetics of lithium transport between the different sites.