In situ measurements of Li ion battery electrode material conductivity:: Application to LixCoO2 and conversion reactions

An electrochemical cell, based on a specifically designed substrate, was used to monitor in an in situ manner the conductivity variations of various thin film electrode materials, grown by laser ablation, during their electrochemical reaction vs Li+/Li-0. The validity of such a new setup was first demonstrated for the well-known LixCoO2 insertion electrode and further extended to an Fe2O3 electrode that reacts with Li through a conversion as opposed to an insertion process. For LixCoO2, a drastic increase in the conductivity near the solid solution domain was observed, confirming the insulator/metal transition previously observed near x = 0.9. For the transport properties of alpha-Fe2O3 thin films as a function of their Li uptake and removal, we noted the semi-metal-like behavior of the Li2O/M matrix, with room-temperature conductivity values ranging from 1 to 25 S/cm. Such results are in favor of mass transport limitations to explain high polarization observed for conversion reactions.