Synergistic Effect between S and Se Enhancing the Electrochemical Behavior of Se_xS_y in Aqueous Zn Metal Batteries

Developing high-capacity conversional cathode materials for aqueous Zn batteries is promising to improve their energy densities but challenging as well. In this work, three kinds of selenium–sulfur solid solutions and their composites (denoted as SeS₁₄ @ 3D-NPCF, SeS_5.76 @ 3D-NPCF, and SeS_2.46 @ 3D-NPCF) are proposed and systematically investigated. Due to the introduction of Se and its synergistic effect with S, their physical and electrochemical properties are manipulated; in particular, by optimizing the Se content in these composites, SeS_5.76 @ 3D-NPCF shows a capacity of 1222 mAh g⁻¹ and flat plateau of 0.71 V at 0.2 A g⁻¹, reaching an ultrahigh energy density of 867.6 Wh kg⁻¹ (based on SeS_5.76), superior rate capacity of 713 mAh g⁻¹ at 5 A g⁻¹, and stable cycling of 75% capacity retention after 500 cycles. In addition, the Zn storage kinetics is determined by the discharge process, during which SeS_5.76 @ 3D-NPCF is converted into ZnSe and ZnS. More importantly, theoretical calculations reveal that Se can tailor the electron density difference, band structure, and reaction energy of S, which increase its conductivity and reactivity to facilitate the electrochemical reaction with Zn. This work explores high performance conversional cathode materials for aqueous Zn metal batteries and presents an effective strategy to modify their intrinsic properties.