First-Principles Calculations to Deciphering Sodium-Ion Storage—2D-Sulfide vs. Oxide

Energy storage technologies are essential for maximizing the utilization of clean and renewable energy sources. While lithium-based systems are widely used in rechargeable batteries, their high cost due to lithium scarcity drives the search for alternatives based on more abundant elements [1]. Sodium-ion batteries (NIBs) are a promising alternative due to the low cost, natural abundance, and environmental friendliness of sodium [2]. Despite these advantages, further advancements in NIBs require the development of materials with superior electrochemical performance and energy density. Transition metal-based materials are particularly promising for NIBs due to their high theoretical capacity. Among these, sulfides are considered superior to oxides because of their enhanced conductivity and charge transfer properties [3]. In this study, we studied the tungsten sulfide (WS2) microflowers that were synthesized via thermal sulfurization of tungsten trioxide (WO3) [4]. The synthesized resulting WS2 nanostructures exhibited a higher specific capacity and more stable performance compared to their oxide counterparts [4]. To understand the underlying mechanisms, first-principles calculations based on Density Functional Theory (DFT) were conducted to investigate the electronic structure and interactions of both nanostructures with sodium ions. Our results indicate that conductivity decreases from the bulk to the 2D counterparts in both materials. Additionally, the oxide nanostructure demonstrated higher energy diffusion barriers (0.50 eV) compared to the 2D WS2 (energy barriers as low as 0.05 eV). These findings are explained by the binding energy of sodium ions. For 2D WO3, sodium binds strongly (-1.00 eV for the weakest adsorption site), whereas the interaction with 2D WS2 is much weaker (+0.47 eV for the adsorption site), resulting in reduced mobility on the oxide. This study is the first to investigate the storage performance of WO3 and WS2 using experimental and theoretical perspectives, contributing to the development of novel electrode materials for sodium-ion batteries.<br/><b>Acknowledgements</b><br/>The authors thank PRH.49 (PRH-ANP UFABC) and CNPq (grant 308428/2022-6) for funding and the UFABC Multiuser Computational Center (CCM-UFABC) for the computational resources provided.<br/><b>References</b><br/>[1] Pramanik, A. et al., <i>Mater. Today Energy</i> 2018, <b>9</b>, 416.<br/>[2] Wang, S. Et al., <i>Mater. Chem. Front.</i> 2023, <b>7</b>, 2779.<br/>[3] Liu, C. et al., <i>Adv. Mater.</i> 2010, <b>22</b>, 28.<br/>[4] Sengupta, S., et al. <i>Small</i> 2024 2403321.