Asymmetric Zn–N ₄ –S configuration via second-shell sulfur doping for ultralow-polarization aqueous zinc–sulfur batteries

Abstract The development of aqueous zinc–sulfur batteries (AZSBs) is primarily plagued by the sluggish kinetics and poor reversibility of the solid–solid sulfur conversion reaction. Herein, we report a Zn single-atom catalyst embedded within a N, S-doped porous carbon matrix (Zn SAs/NSC) as an efficient sulfur host to tackle these challenges. A one-step pyrolysis of zeolitic imidazolate frameworks (ZIFs) with potassium thiosulfate (K2S2O3) was employed to produce hierarchical pore structure with large specific surface area of 2135.5 m2·g−1 and incorporation of sulfur atoms in the second coordination shell of Zn–N4 sites, resulting in an asymmetric Zn–N4–S configuration. When employed as a sulfur host, the Zn SAs/NSC-800-based cathode delivers a notable discharge capacity of 1610.6 mAh·g−1 at 0.1 A·g−1 with an ultralow polarization voltage of 0.276 V. It also exhibits good rate capability (1229.1 mAh·g−1 at 5 A·g−1) and long-term cycling stability (60% capacity retention after 1000 cycles). Density functional theory (DFT) calculations reveal that the Zn–N4–S sites can enhance the adsorption energy of ZnS (−2.08 eV) and facilitate electron transfer, thereby reducing the energy barrier for the solid–solid conversion. This work demonstrates the significant roles of metal single-atom coordination microenvironment in enhancing the electrochemical performance of AZSBs.