Engineered Sodium Metal Anodes: Tackling Sulfur-Derivative Challenges for Advanced Sodium–Sulfur Batteries

Abstract

The development of room temperature sodium–sulfur (RT Na─S) batteries has been significantly constrained by the dissolution/shuttle of sulfur-derivatives and the instability of sodium anode. This study presents an engineered sodium metal anode (NBS), featuring sodium bromide (NaBr) along with sodiophilic components like tin metal (Sn) and sodium-tin (Na─Sn) alloy. This configuration exhibits high plating/stripping reversibility with minimal nucleation/growth barriers in an ester-based electrolyte, allowing stable cycling of symmetric cells at 2 mA cm⁻²/2 mA h cm⁻² for over 2000 h at a low overpotential of 30 mV. Importantly, the weak adsorption and reduced electron transfer towards sulfur-derivatives, along with the facile dissociation of Na₂S₂/Na₂S, effectively minimize the accumulation of sulfur-derivatives, thereby improving the interfacial stability of the NBS electrode in sulfur-derivatives-involved conditions. As a result, the NBS anode endows the Na─S full cells paired with either a Co-NMCN@S or SPAN cathode superior electrochemical performance, with the SPAN//NBS system delivering an outstanding reversible capacity of 1639.5 mA h g⁻¹ and a low degradation rate of 0.06% per cycle at 0.5C. This study elucidates the complex deposition/dissolution kinetics and interface chemistry associated with sulfur species, providing valuable insights for enhancing sodium anodes in practical RT Na─S systems.