Simultaneous pre-intercalation of caesium and sodium ions into vanadium oxide bronze nanowires for high-performance aqueous zinc-ion batteries

Abstract

Vanadium oxide derivatives as cathode materials for aqueous zinc-ion batteries have received increasing attention owing to their multivalent vanadium species and open-frame crystal structures. Herein, heavyweight and lightweight alkali metal ions as pillars involving caesium and sodium ions were simultaneously pre-intercalated into vanadium oxide bronze nanowires in the presence of polyethylene glycol. The pre-intercalation of Na⁺ ions contributed to the formation of the two-dimensional tunnel structure of vanadium oxide bronzes. Remarkably, the accommodation of additional Cs⁺ ions in the interlayer region facilitated an expansion of the interplanar spacing and an increase in the surface oxygen defects. When used in aqueous zinc-ion batteries, Na_0.33Cs_0.03V₂O₅ (NCVO) cathodes achieved a high reversible capacity of 376.5 mA h g⁻¹ at 0.1 A g⁻¹ in addition to excellent 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 revealed that the co-intercalation of caesium and sodium ions contributed 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.