Layered Ti1-xFexS2 Cathode Materials with Anionic Redox Chemistry for Mg Storage

Rechargeable magnesium batteries (RMBs) are a promising alternative to lithium-ion batteries because of the high capacity and crustal abundance of magnesium. However, RMBs are primarily plagued by low-energy-density of traditional cathode materials, which utilize transition-metal cationic redox chemistry. Herein, a new family of layered Ti 1- x Fe x S 2 (0 < x < 1) materials is proposed to assess anionic redox and boost the energy density of RMBs. The structural stability and redox activity are systematically investigated using first-principles calculations and operando experimental techniques. It is found that layered Mg n Ti 1- x Fe x S 2 materials are stable below x = 0.5, forming the solid-solution sulfides. The Mg n Ti 0.75 Fe 0.25 S 2 sample is experimentally shown to offer a high operating voltage of 1.8 V, a competitive energy density of 103 mAh g −1 , and better cycling stability compared to prototype TiS 2 material. Both cations (Ti and Fe) and anion (S) are revealed to take part in the redox reaction. The new family of layered Ti 1- x Fe x S 2 cathodes with joint cationic and anionic redox chemistry proposed in this work are promising high-energy cathode candidates for RMBs.