Self-intercalated quasi-2D structured V5Se8 wrapped with multi-walled carbon nanotubes toward advanced sodium ion batteries

Abstract

Sodium-ion batteries (SIBs) have attracted much focus as electrochemical energy storage devices with unlimited potential for upcoming large-scale energy storage applications. Nevertheless, sodium ions with large radius and high mass can hinder sodium ions from diffusing into the electrode material, resulting in poor energy/power density and cycling stability. Therefore, a highly conductive three-dimensional carbon network composed of V5Se8 with a self-intercalated layer structure and one-dimensional multi-walled carbon nanotubes (MWCNTs) has been prepared using a straightforward one-step selenization process. This three-dimensional structure can increase the reversible sodium ion storage capacity and structural stability during the cycling process. The obtained V5Se8/MWCNTs electrodes have outstanding rate capacity (250 mAh g−1 at 10 A g−1) and tremendous initial reversible capacity (353 mAh g−1 at 0.2 A g−1). After 1000 cycles, they also obtain adequate cycling stability (323 mAh g−1 at 2 A g−1). The reaction mechanism of V5Se8/MWCNTs electrode in SIBs has been studied using X-ray diffraction (XRD) and transmission electron microscopy (TEM) methods, demonstrating that this electrode experiences a reversible phase transition between V5Se8 and V throughout the Na + insertion/extraction procedures. The full cell can offer a discharge plateau of 2.02 V when coupled with a Na3V2(PO4)2F3@reduced graphene oxide cathode. It also has an excellent discharge capacity of 177 mAh g−1 at 0.1 A g−1 and good cycling stability of 79 mAh g−1 after 1000 cycles at 1 A g−1.