Tungsten diselenide nanoplates as advanced lithium/sodium ion electrode materials with different storage mechanisms

Transition-metal dichalcogenides (TMDs) exhibit immense potential as lithium/ sodium-ion electrode materials owing to their sandwich-like layered structures. To optimize their lithium/sodium-storage performance, two issues should be addressed: fundamentally understanding the chemical reaction occurring in TMD electrodes and developing novel TMDs. In this study, WSe 2 hexagonal nanoplates were synthesized as lithium/sodium-ion battery (LIB/SIB) electrode materials. For LIBs, the WSe 2 -nanoplate electrodes achieved a stable reversible capacity and a high rate capability, as well as an ultralong cycle life of up to 1,500 cycles at 1,000 mA·g –1 . Most importantly, in situ Raman spectroscopy, ex situ X-ray diffraction (XRD), transmission electron microscopy, and electrochemical impedance spectroscopy measurements performed during the discharge–charge process clearly verified the reversible conversion mechanism, which can be summarized as follows: WSe 2 + 4Li + + 4e – ↔ W + 2Li 2 Se. The WSe 2 nanoplates also exhibited excellent cycling performance and a high rate capability as SIB electrodes. Ex situ XRD and Raman spectroscopy results demonstrate that WSe 2 reacted with Na + more easily and thoroughly than with Li + and converted to Na 2 Se and tungsten in the 1 st sodiated state. The subsequent charging reaction can be expressed as Na 2 Se → Se + 2Na + + 2e – , which differs from the traditional conversion mechanism for LIBs. To our knowledge, this is the first systematic exploration of the lithium/sodium-storage performance of WSe 2 and the mechanism involved.