Phase transition and surface morphology effects on optical, electrical and lithiation/delithiation behavior of nanostructured Ce-doped V2O5 thin films

Cerium doped V2O5 thin films were prepared by the sol−gel process. X-ray diffraction analysis revealed the phase transition from α-V2O5 orthorhombic to β-V2O5 tetragonal structure by annealing at 400 °C. The SEM and AFM images revealed that annealing temperature changed the surface morphology of the V2O5 films from fiber like wrinkle network to elongated sheets. Also, the particle shape was significantly influenced by Ce doping and a nanorod-like morphology was formed at 1.5 mol% Ce−doped V2O5. Power spectral density analysis indicated that surface roughness and fractal dimension of β−V2O5 increase by Ce doping. Optical measurement showed that the band gap narrowing (from 2.68 to 2.28 eV) occurred when the annealing temperature and dopant concentration increased. The variation of activation energy of the films was explained based on the small polaron hopping mechanism. The α−V2O5 film showed enhanced lithium−ion storage capacity compared to pristine β−V2O5 film and 1 mol% Ce−doped α−V2O5 thin film revealed the best ion storage capacity (Qa=207.19 mC/cm2, Imax=4.13 mA/cm2 at scan rate of ν=20 mV/s).