Lithium transport through graphite electrodes that contain two stage phases

The lithium transport through graphite electrodes that contain two stage phases has been investigated in 1 M LiAsF6-EC/DEC (ethylene carbonate/diethyl carbonate) non-aqueous solution by using potentiostatic current transient technique supplemented by lithium charging/discharging experiments and a.c. impedance spectroscopy. An attractive interaction between the intercalated lithium ions and the graphite lattice is indicated from the decreased diffusivity value with increasing lithium content in the lithiated graphite electrode in the presence of a single stage phase. This attractive interaction gives rise to the stage transformation in the electrode, which is characterized by potential plateaus in the charge/discharge curves. From the results of the potentiostatic current transients, it is suggested that the stage transformation in the lithiated graphite electrode is accompanied by the limited transport of lithium through the electrode for which the stress generated by the stage phase boundary is responsible. The stress-controlled transport of lithium through the graphite structure is substantiated by the occurrence of hysteresis in the potential profile during the lithium intercalation and de-intercalation. (C) 1998 Elsevier Science S.A.