Simultaneous Pre-Intercalation of Caesium and Sodium Ions into Vanadium Oxide Bronze Nanowires for High-Performance Aqueous Zinc-Ion Batteries

Vanadium oxide derivatives as cathode materials of aqueous zinc-ion batteries have received incremental attention owing to their multivalences of vanadium and open-frame crystal structures. Herein, the lightweight and heavyweight alkali metal ions as pillars involved to sodium and caesium ions are simultaneously pre-intercalated into vanadium oxide bronze nanowires in the presence of polyethylene glycol. The pre-intercalation of Na+ ions contributes to forming the two-dimensional tunnel structure of vanadium oxide bronzes. Remarkably, the accommodation of additional Cs+ ions in the interlayer region facilitates the expansion of interplanar spacing and the increase of surface oxygen defects. For aqueous zinc-ion batteries, Na0.33Cs0.03V2O5 (NCVO) cathodes achieve a high reversible capacity of 376.5 mAh g-1 at 0.1 A g-1, in addition to an excellence long-term cycling stability with a capacity retention of 95.4% over 1500 cycles at 5.0 A g-1. Furthermore, the results from ex situ X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) analyses reveal that the co-intercalation of sodium and caesium ions contributes to the reversible phase change of vanadium oxide bronzes during repeated Zn2+ ion deintercalation-intercalation processes after the conversion reaction observed in the initial discharge process, which opens up a route to develop high-performance cathode materials.