Hybrid Li-Ion and Li-O2 Battery Enabled by Oxyhalogen-Sulfur Electrochemistry

Summary The large voltage hysteresis between charge and discharge results in significant energy loss, which hinders practical application of the high-energy Li-O 2 battery. Oxyhalogen-sulfur electrochemistry offers a new hybrid Li-ion/Li-O 2 battery, where both Li ions and O anions are reversibly stored in the MoS 2 structure. A Li 2 MoO 2 S 2 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 Li 2 MoO 2 S 2 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 MoS 2 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 Li 2 MoO 2 S 2 is isostructural to the Li 2 MoO 4 rather than adopting structures of other known molybdenum oxysulfides.