Synergistic engineering of amorphous network and oxygen vacancies in vanadium oxides for enhanced sodium-ion storage

In recent years, vanadium oxide (V2O5) as the anode material of sodium ion batteries (SIBs) has been widely concerned. However, it suffers poor cycling stability derived from the narrow distance between two vanadium atoms in adjacent bilayers. In this work, V2O5 with oxygen vacancies (Vos) and amorphous region (V2O5-Vo-A) was synthesized by pyrolyzing and reducing chitosan-VO3- gel under Ar/H2. Amorphous region can inhibit volume expansion during Na+ deintercalation and improve the pseudocapacitance response. When used as anode materials for SIBs, V2O5-Vo-A electrode has excellent cycling performance (260 mAh g−1 at 0.1 A g−1 after 360 cycles) and superior rate performance (208 mAh g−1 at 1 A g−1). Density functional theory (DFT) calculations reveal that Vos significantly increase charge density at the entire Fermi energy level and adjacent bilayers distance to 4.76 Å, which result enhanced binding energy of Na+ (-1.32 eV) and decreasing volume change of 0.87 % after Na+ adsorption. This research presents a new method to improve the Na+ storage performance of metal oxides, which is expected to be generalized to other metal oxides electrode materials.