Copper-Ion-Mediated Selenium Electrochemistry Enables 3.5 V Selenium Batteries

Selenium (Se) is an attractive cathode candidate for rechargeable batteries owing to its high theoretical capacity and favorable electronic conductivity. However, conventional Se batteries relying on alkali metal-ion charge carriers are plagued by low operating voltages (<2.1 V), sluggish kinetics, and polyselenide shuttling. In this study, we extend copper-ion-mediated selenium electrochemistry from aqueous systems to nonaqueous electrolytes by identifying a Cu(ClO 4 ) 2 /carbonate electrolyte that enables reversible Cu-mediated Se conversion. The copper-ion mediation mechanism produces insoluble and highly conductive Cu x Se intermediates, which effectively suppress polyselenide dissolution and shuttling while enabling rapid reaction kinetics, as reflected by the low polarization of ∼0.1 V. Moreover, this approach elevates the selenium redox potential from below −0.5 V to +0.5 V vs SHE, enabling a hybrid lithium–selenium battery with a 3.5 V discharge voltage, compared to ∼2.0 V in conventional alkali metal-Se systems. This work demonstrates the feasibility of implementing Cu-mediated selenium electrochemistry in nonaqueous media and achieves a high-voltage Se-based battery.