Dual synergistic effects assisting Cu-SeS₂ electrochemistry for energy storage

Selenium sulfide (SeS₂) features higher electronic conductivity than sulfur and higher theoretical capacity and lower cost than selenium, attracting considerable interest in energy storage field. Although nonaqueous Li/Na/K-SeS₂ batteries are attractive for their high energy density, the notorious shuttle effect of polysulfides/polyselenides and the intrinsic limitations of organic electrolyte have hindered the deployment of this technology. To circumvent these issues, here we design an aqueous Cu-SeS₂ battery by encapsulating SeS₂ in a defect-enriched nitrogen-doped porous carbon monolith. Except the intrinsic synergistic effect between Se and S in SeS₂, the porous structure of carbon matrix has sufficient internal voids to buffer the volume change of SeS₂ and provides abundant pathways for both electrons and ions. In addition, the synergistic effect of nitrogen doping and topological defect not only enhances the chemical affinity between reactants and carbon matrix but also offers catalytic active sites for electrochemical reactions. Benefiting from these merits, the Cu-SeS₂ battery delivers superior initial reversible capacity of 1,905.1 mAh g^-1 at 0.2 A g^-1 and outstanding long-span cycling performance over 1,000 cycles at 5 A g^-1. This work applies variable valence charge carriers to aqueous metal-SeS₂ batteries, providing valuable inspiration for the construction of metal-chalcogen batteries.