Understanding the Role of Lithium Ions and Electron Transport in a Multi-Electrode System Designed for Lithium-Oxygen Batteries

Abstract

The formation and decomposition of the discharge products (Li2O2) during the charging and discharging processes in Li-oxygen batteries are the main reactions that drive this technology, initiated at a solid-liquid-gas phase boundary involving Li+, O2 and e- in the cathode compartment. However the mechanistic contribution of each of these component to the electrochemical reactions in a given cell remains unknown. In this study, we seek to understand the role of Li+ and e- at the phase boundary by developing a dual-cathode system containing a lithium conducting electrode(Li3N) and an electron conducting electrode(LiI) separated by nickel mesh. It was observed that, the LiI has the tendency to form reduced oxygens on the electrode surface via I-/I3 - redox couple, while Li-ions migrate to the electrode surface by the Li-ion conductive effect of the Li3N in the reactions leading to the discharge product formation. The discharge products on the Li3N electrode were found to be oxygen-rich, while those on the LiI electrode surface were found to be oxygen-deficient. Electrochemical analyses revealed that the cells could discharge up to a capacity of 3.74mAh/cm2 at a current density of 0.1mA/cm2 with an over potential of 0.59V upon charging. At the same current density the cells were able to discharge-charge up to 184 cycles at a cut-off capacity of 0.2mAh/cm2.