Core-Shell Structure and Interaction Mechanism of γ-MnO Coated Sulfur for Improved Lithium-Sulfur Batteries.

Lithium-sulfur batteries have attracted worldwide interest due to their high theoretical capacity of 1672 mAh g and low cost. However, the practical applications are hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, the authors have fabricated a solid core-shell γ-MnO -coated sulfur nanocomposite through the redox reaction between KMnO and MnSO . The multifunctional MnO shell facilitates electron and Li transport as well as efficiently prevents polysulfide dissolution via physical confinement and chemical interaction. Moreover, the γ-MnO crystallographic form also provides one-dimensional (1D) tunnels for the Li incorporation to alleviate insoluble Li S /Li S deposition at high discharge rate. More importantly, the MnO phase transformation to Mn O occurs during the redox reaction between polysulfides and γ-MnO is first thoroughly investigated. The S@γ-MnO composite exhibits a good capacity retention of 82% after 300 cycles (0.5 C) and a fade rate of 0.07% per cycle over 600 cycles (1 C). The degradation mechanism can probably be elucidated that the decomposition of the surface Mn O phase is the cause of polysulfide dissolution. The recent work thus sheds new light on the hitherto unknown surface interaction mechanism and the degradation mechanism of Li-S cells.