Deciphering Sodium-Ion Storage: 2D-Sulfide versus Oxide Through Experimental and Computational Analyses.

Transition metal derivatives exhibit high theoretical capacity, making them promising anode materials for sodium-ion batteries. Sulfides, known for their superior electrical conductivity compared to oxides, enhance charge transfer, leading to improved electrochemical performance. Here, a hierarchical WS 2 micro-flower is synthesized by thermal sulfurization of WO 3 . Comprising interconnected thin nanosheets, this structure offers increased surface area, facilitating extensive internal surfaces for electrochemical redox reactions. The WS 2 micro-flower demonstrates a specific capacity of ≈334 mAh g -1 at 15 mA g -1 , nearly three times higher than its oxide counterpart. Further, it shows very stable performance as a high-temperature (65 °C) anode with ≈180 mAh g -1 reversible capacity at 100 mA g -1 current rate. Post-cycling analysis confirms unchanged morphology, highlighting the structural stability and robustness of WS 2 . DFT calculations show that the electronic bandgap in both WS 2 and WO 3 increases when going from the bulk to monolayers. Na adsorption calculations show that Na atoms bind strongly in WO 3 with a higher energy diffusion barrier when compared to WS 2 , corroborating the experimental findings. This study presents a significant insight into electrode material selection for sodium-ion storage applications.