UC San Diego

The large voltage hysteresis between charge and discharge results in significant energy loss, which hinders practical application of the high-energy Li-O2 battery. Oxyhalogen-sulfur electrochemistry offers a new hybrid Li-ion/Li-O2 battery, where both Li ions and O anions are reversibly stored in the MoS2 structure. A Li2MoO2S2 compound is formed as the main discharge product that has never been previously observed in the literature. The reaction mechanism and the structure of the Li2MoO2S2 are probed by Raman spectroscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, differential electrochemical mass spectrometry, and UV-visible spectroscopy. The results show that the MoS2 is oxidized during discharge and is recovered during charge. The iodine intermediates play an important role in triggering the sequence of electrochemical and chemical reactions in the cell. The Li2MoO2S2 is isostructural to the Li2MoO4 rather than adopting structures of other known molybdenum oxysulfides.