Mixed Anionic and Cationic Redox Chemistry in a Tetrathiomolybdate Amorphous Coordination Framework
Qi Zhu, Jiande Wang, Xuelian Liu, Neil Ebejer, Darsi Rambabu, Alexandru Vlad
Abstract
Abstract We report the electrochemistry of a hitherto unexplored Na 2 MoS 4 phase as a conversion electrode material for Na‐ and Li‐ion batteries. The material adopts an amorphous coordination polymer structure with mixed Mo and S valences. XPS and XRD analysis reveal a complex interplay between Mo and S redox chemistry, while excluding the formation of free sulfur, lithium sulfide, or other crystalline phases. Na 2 MoS 4 behaves as a mixed ionic–electronic conductor, with electronic conductivity of 6.1×10 −4 S cm −1 , that permits carbon‐free application in an electrochemical cell. A reversible capacity of up to 500 mAh g −1 was attained, corresponding to a five‐electron redox exchange, with species ranging from <Na <1 MoS 4 > (highest oxidized state) to <Na >5 MoS 4 > (lowest oxidized state). This study emphasizes the excellent charge‐storage performances of Na 2 MoS 4 for Li‐ or Na‐ion batteries, and enriches the emerging library and knowledge of sulfide phases with mixed anionic and cationic redox properties.