A Magnesium/Lithium Hybrid-Ion Battery with Modified All-Phenyl-Complex-Based Electrolyte Displaying Ultralong Cycle Life and Ultrahigh Energy Density.

Magnesium/lithium hybrid-ion batteries (MLHBs) combine the advantages of high safety and fast ionic kinetics, which enable them to be promising emerging energy-storage systems. Here, a high-performance MLHB using a modified all-phenyl complex with a lithium bis(trifluoromethanesulfonyl)imide electrolyte and a NiCo 2 S 4 cathode on a copper current collector is developed. A reversible conversion involving a copper collector with NiCo 2 S 4 efficiently avoids the electrolyte dissociation and diffusion difficulties of Mg 2+ ions, enabling low polarization and fast redox, which is verified by X-ray absorption near edge structure analysis. Such combination affords the best MLHB among all those ever reported, with a reversible capacity of 204.7 mAh g -1 after 2600 cycles at 2.0 A g -1 , and delivers an ultrahigh full electrode-basis energy density of 708 Wh kg -1 . The developed MLHB also achieves good rate performance and temperature tolerance at -10 and 50 °C with a low electrolyte consumption. The hybrid-ion battery system presented here could inspire a broad set of engineering potentials for high-safety battery technologies and beyond.