Effect of aging and hydrothermal treatment on electrochemical performance of chemically pre-intercalated Na–V–O nanowires for Na-ion batteries

Abstract

A chemical pre-intercalation approach was used to synthesize Na-containing vanadium oxide nanowires for use as Na-ion battery cathodes. The synthesis method was based on a sol–gel process followed by aging and/or hydrothermal treatment. We have for the first time shown that addition of sodium salt into the hydrothermally treated precursor mixture leads to a higher content of chemically pre-intercalated Na⁺ ions in the crystal structure of produced layered vanadium oxides. Further, the inclusion of an aging step was found to be crucial for the formation of bilayered Na_xV₂O₅ phase with high capacity in Na-ion cells. Single-phase bilayered Na_xV₂O₅ nanowires, obtained after the hydrothermal treatment of four-day aged precursor, demonstrated a record high initial discharge capacity of 365 mA h g⁻¹. The hydrothermal treatment was shown to improve crystallinity of nanowires, leading to the better electrochemical stability of electrodes. Our results demonstrate the potential of chemical pre-intercalation synthesis method to develop high-capacity Na-ion battery cathodes. The ability to control various parameters in the multi-step chemical pre-intercalation approach opens a door to employing this method for the synthesis of electrode materials for other beyond lithium-ion electrochemical systems, such as Mg-ion and K-ion batteries.