In Situ Copper‐Mediated Electron Bridge Revolutionizes Aqueous Sulfur‐Based Batteries

The practical application of sulfur-based batteries remains challenged by the sluggish charge transfer kinetics and structural instability of sulfur cathodes, largely attributed to the absence of efficient electron transport pathways and robust electrode architecture. Herein, we present an in situ electron bridge construction strategy by introducing a transition metal to tailor the electronic properties and reinforce the structure of sulfurized polyacrylonitrile (SPAN) cathode. The dynamic d-p orbital hybridization between copper and SPAN within the electron bridge promotes bandgap closure, shifting the electronic character from a semiconducting state toward a metallic state, thereby establishing high-speed electron transfer channels and accelerating redox kinetics. Simultaneously, the self-assembled copper-modified SPAN (CuSPAN), driven by in situ thermodynamically-favorable process, intrinsically reinforces the cathode structure, conferring exceptional long-term operational stability. As a result, the aqueous CuSPAN-based battery achieves a high reversible capacity of 760 mAh g^-1 at 3 C and outstanding cyclic stability with 79.2% capacity retention over 50 000 cycles at 15 C, superior to previously reported aqueous sulfur batteries. To verify the practicality, a flexible pouch cell is built based on the CuSPAN cathode, Zn anode, and gel electrolytes, delivering a stable operating voltage (1.2 V), high energy density (950 Wh kg^-1), and remarkable cycling stability even under various harsh conditions.