Layered Oxysulfides Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>2</sub><i><sub>m</sub></i><sub>-</sub><sub>0.5</sub>S<i><sub>m</sub></i><sub>+1</sub> (<i>m</i> = 1, 2, and 3) as Insertion Hosts for Li Ion Batteries

The layered oxysulfides Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>2</sub><i><sub>m</sub></i><sub>-</sub><sub>0.5</sub>S<i><sub>m</sub></i><sub>+1</sub> (<i>m</i> = 1−3) consist of alternating perovskite-type Sr<sub>2</sub>MnO<sub>2</sub> layers and copper sulfide layers. The copper ions can be replaced electrochemically and reversibly by Li. The lithiated materials were studied by Li MAS NMR, and Li resonances were observed with shifts that could be rationalized based on the number of sulfide layers. The materials were cycled versus Li and showed enhanced capacity retention in comparison to pure Cu<sub>2</sub>S; the good electrochemical performance was ascribed to the presence of the layered framework structure and rapid Li<sup>+</sup> and Cu<sup>+</sup> conductivity in the sulfide layers.