Nickel pre-intercalated bilayer vanadium pentoxide hydrate for reversible structural evolution in Na-ion battery cathode

Layered vanadium oxides, due to their high specific capacity and the multiple oxidation states of vanadium, are attractive candidates as cathode materials for sodium-ion batteries (SIBs). To meet the requirements of increasing interlayer spacing and significantly improving structural stability, herein, nickel pre-intercalated bilayer vanadium pentoxide hydrate, Ni0.28V2O5 center dot 0.62 H2O (referred to as NVO) is synthesized successfully. The interlayer water molecules significantly increase the interlayer distance of the bilayer vanadium pentoxide. At the same, by forming a stable interlayer NiO6 octahedron, the intercalated Ni atoms effectively relieve the big change of volume during the Na ions insertion/extraction process and effectively inhibit the interlayered water molecules escape in charge/discharge process. Due to the big interlayer distance and excellent structural stability, the NVO electrode exhibits an excellent electrochemical performance. Except for the first few cycles, a high reversible capacity of about 260 mAh g(-1) is obtained and the mean fade is only 0.5% per cycle. In addition, the excellent Na storage mechanism of the NVO electrode is also explored in detail by in situ XRD.