Water-Pillared Sodium Vanadium Bronze Nanowires for Enhanced Rechargeable Magnesium Ion Storage

Owing to the advantages of high safety, low cost, high theoretical volumetric capacities, and environmental friendliness, magnesium-ion batteries (MIBs) have more feasibility for large-scale energy storage compared to lithium-ion batteries. However, lack of suitable cathode materials due to sluggish kinetics of magnesium ion is one of the biggest challenges. Herein, water-pillared sodium vanadium bronze nanowires (Na₂ V₆ O₁₆ ·1.63H₂ O) are reported as cathode material for MIBs, which display high performance in magnesium storage. The hydrated sodium ions provide excellent structural stability. The charge shielding effect of lattice water enables fast Mg²⁺ diffusion. It exhibits high specific capacity of 175 mAh g^-1 , long cycle life (450 cycles), and high coulombic efficiency (≈100%). At high current density of 200 mA g^-1 , the capacity retention is up to 71% even after 450 cycles (compared to the highest capacity), demonstrating excellent long-term cycling performance. The nature of charge storage kinetics is explored. Furthermore, a highly reversible structure change during the electrochemical process is proved by comprehensive electrochemical analysis. The remarkable electrochemical performance makes Na₂ V₆ O₁₆ ·1.63H₂ O a promising cathode material for low-cost and safe MIBs.