Cost effective synthesis of 3-dimensional V₄O₉: A promising high-capacity lithium cathode

The earthly abundant vanadium exhibits multi-oxidation states and different crystalline structures in their oxide compounds offering unique electrical, opto-electronic, and catalytic properties to be applicable for various applications including energy storage materials. The stable vanadium oxides (V2O5, VO2, V2O3) are mostly studied while metastable oxides such as V4O9 is less explored. The latter possesses a tridimensional (3D)-tunnel defect type structure with different polyhedral wherein VO5 pyramids and VO6 octahedra are connected by corner oxygen atoms from the VO4 tetrahedra with V4+ and V5+ oxidation states, respectively, making it an appealing host candidate for lithium-ions insertion. Herein, we present a cost-effective single pot synthesis of 3D V4O9 nanoparticles using versatile low temperature solvothermal method. The obtained material has been fully characterised in terms of phase identity and crystal structure using x-ray diffraction, Raman spectroscopy and high-resolution-transmission-electron-microscopy while surface composition and valence- and/ oxidation states using x-ray photoelectron spectroscopy followed by investigation of its electrochemical performance against lithium. Upon first discharge, V4O9 could intercalate similar to 6 Li+ per formula unit corresponding to highest discharge capacity of 464.5 mA h g(-1) and a reversible first Coulombic efficiency of 75.3% between 1.5 - 4.0 V against Li in a half-cell configuration. In the long run, the V4O9 exhibited a reversible capacity of 160.8 mA h g(-1) at 100 mA g(-1) even after 2000 cycles against lithium rendering it as suitable positive electrode with high capacity and cyclability for lithium-ion battery applications.