Designing a Magnesium/Sodium Hybrid Battery Using Hierarchical Iron Selenide Architecture as Cathode Material and Modified Dual-Ion Salts in Ether as Electrolyte.

We developed a magnesium/sodium (Mg/Na) hybrid battery using a hierarchical disk-whisker FeSe 2 architecture (HD-FeSe 2 ) as the cathode material and a modified dual-ion electrolyte. The polarizable Se 2- anion reduced the Mg 2+ migration barrier, and the 3D configuration possessed a large surface area, which facilitated both Mg 2+ /Na + cation diffusion and electron transport. The dual-ion salts with NaTFSI in ether reduced the Mg plating/stripping overvoltage in a symmetric cell. The hybrid battery exhibited an energy density of 260.9 Wh kg -1 and a power density of 600.8 W kg -1 at 0.2 A g -1 . It showed a capacity retention of 154 mAh g -1 and a Coulombic efficiency of over 99.5% under 1.0 A g -1 after 800 long cycles. The battery also displayed outstanding temperature tolerance. The findings of 3D architecture as cathode material and hybrid electrolyte provide a pathway to design a highly reliable Mg/Na hybrid battery.