Layered Ti _{1‐ <i>x</i>} Fe _<i>x</i> S ₂ 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 &lt; x &lt; 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.