Hybrid Redox Chemistry in Defective Titanium Polyanion Nanobelt Cathodes for Advanced Magnesium–Ion Batteries

Abstract Parasitic reactions have hampered transition metal chalcogenide cathodes in magnesium−ion batteries (MIBs), especially for conversion−type cathodes. To fully harness its high theoretical capacity and restrict undesirable side reactions, a defective titanium polyanion cathode ( V _s −TiS ₃ ) with exposed (001) facets is prepared via a fast−quenching treatment. The performance of the cathode material is investigated in MIBs for the first time, demonstrating a new hybrid energy storage mechanism involving both insertion and conversion reactions. Moreover, the defective TiS ₂ formed during cycling is found to have a strong adsorption effect on the side products of magnesium polysulfides (MgS _x ), boosting magnesium storage performance. Consequently, the electrodes delivered a substantial capacity of 717.3 mAh g ⁻¹ at 25 mA g ⁻¹ , and a high capacity of 291.5 mAh g ⁻¹ at 500 mA g ⁻¹ after 100 cycles, surpassing the performance of previously reported MIBs at the same current density. When employed in pouch cells, a high energy density of 220 Wh kg ⁻¹ is achieved. Lastly, this cathode material is also adapted for other mono/multivalent metal−ion batteries (e.g., Li ⁺ , Na ⁺ , Al ³⁺ ), demonstrating its versatility.