Bifunctional Electrolyte Additive in Room-Temperature Sodium–Sulfur Batteries

Room-temperature sodium–sulfur (RT Na–S) batteries have been restricted by difficulties on both electrodes: the utilization of active sulfur still falls short of expectations, and the Na anode suffers from dendrite formation and poor interface stability. Although sulfide solid electrolytes can address these issues, undesirable side reactions pose difficulties in solid–solid interfacial contact. Inspired by this, a sulfide (P2S5/Na2S)-containing electrolyte was employed. Utilizing liquid–solid reactions not only increases battery capacity by forming a tightly connected active material with the Cu current collector but also generates a uniform passivation layer on the Na anode, stabilizing the electrode interface. This dual-functional mechanism leads to unprecedented performance, retaining a capacity of 856 mAh g–1 after 900 cycles at 1C, with an average Coulombic efficiency of 99.6%. The work introduces a subtle strategy, provides insights into the mechanism of the P2S5/Na2S additive, and demonstrates the feasibility of this approach for improving the performance of RT Na–S batteries.