Overpotential and electrochemical impedance analysis on Cr2O3 thin film and powder electrode in rechargeable lithium batteries

The overpotentials of Cr2O3 thin film and powder electrodes as well as various benchmark anodes and cathodes in rechargeable lithium batteries have been compared by analyzing the galvanostatic voltage profiles. Li-storage in the Cr2O3 electrode through the conversion reaction shows higher overpotential values than through other Li-storage mechanisms. The origins of the high overpotential of the Cr2O3 electrode have been studied by electrochemical impedance spectroscopy. It is found that the ohmic polarization, charge transfer resistance and diffusion impedance of the Cr2O3 electrode decrease significantly with the insertion of lithium and increase with the extraction of lithium. The calculated overpotential contribution from the diffusion impedance is well consistent with the value deduced from the galvanostatic voltage profiles. It means that the sluggish diffusion should be the main origin for high polarization of Cr2O3 electrodes.