Cu2+ Pre-Intercalation Enables Fast and Stable Hydrated Vanadium Pentoxide Nanostructure-Based Cathodes for Magnesium–Sodium Hybrid Ion Batteries

Magnesium–sodium hybrid-ion batteries combine a safe Mg-metal anode with rapid Na+ cathode kinetics, but suitable cathodes remain scarce. Here, Cu2+ preintercalation regulates hydrated V2O5 through three-dimensional nanosheet-assembled architecture evolution, accompanied by modulation of the interlayer water and local V–O coordination. The resulting CVO nanostructure lowers charge-transfer resistance and improves Mg2+/Na+ transport kinetics, delivering a reversible capacity of 203 mAh g–1 at 20 mA g–1 with 95% initial Coulombic efficiency and 85% capacity retention after 200 cycles at 200 mA g–1. This work demonstrates metal-ion preintercalation as an effective strategy for layered hybrid-ion cathodes.