Six-electron-conversion selenium cathodes stabilized by dead-selenium revitalizer for aqueous zinc batteries

Aqueous zinc batteries are attractive for large-scale energy storage due to their inherent safety and sustainability. However, their widespread application has been constrained by limited energy density, underscoring a high demand of advanced cathodes with large capacity and high redox potential. Here, we report a reversible high-capacity six-electron-conversion Se cathode undergoing a ZnSe↔Se↔SeCl₄ reaction, with Br^-/Br_n^- redox couple effectively stabilizes the Zn | |Se cell. This Se conversion, initiated in a ZnCl₂-based hydrogel electrolyte, presents rapid capacity decay (from 1937.3 to 394.1 mAh g_Se^-1 after only 50 cycles at 0.5 A g_Se^-1) primarily due to the dissolution of SeCl₄ and its subsequent migration to the Zn anode, resulting in dead Se passivation. To address this, we incorporate the Br^-/Br_n^- redox couple into the Zn | |Se cell by introducing bromide salt as an electrolyte additive. The generated Br_n^- species acts as a dead-Se revitalizer by reacting with Se passivation on the Zn anode and regenerating active Se for the cathode reaction. Consequently, the cycling stability of the Zn | |Se cell is improved, maintaining 1246.8 mAh g_Se^-1 after 50 cycles. Moreover, the Zn | |Se cell exhibits a specific capacity of 2077.6 mAh g_Se^-1 and specific energy of 404.2 Wh kg^-1 based on the overall cell reaction.