Physicochemical properties of V5+ doped LiCoPO4 as cathode materials for Li-ion batteries

Phase pure olivine type V5+ doped and un-doped LiCoPO4 (LiCo1−xVxPO4 & LiCoP1−xVxO4; x = 0.02, 0.04 and 0.06) were synthesized by combustion method. Compound formation temperature and thermal stability of the materials were studied through thermal analysis. X-ray diffraction pattern shows the prepared material possesses an orthorhombic structure with Pnmb space group. Further the functional group and vibrational analysis were carried out by Fourier Transform Infra-red and Raman spectroscopy techniques. The Scanning Electron Micrographs depicts the irregular shaped morphology with particle agglomeration of the pristine and doped LiCoPO4 materials. The structural variation on addition of dopant on both sites Co2+ & P5+ were revealed from XPS spectra. The electrochemical aspects of these materials were investigated by cyclic voltammetry studies in conjunction with electrochemical impedance spectroscopy and chronoamperommetry measurements to understand the redox reactions and their capacity contribution at higher voltages. The EIS analysis shows that the conductance value was decreased for the vanadium doped samples for both the Co site and P site, which infers that the V5+ addition doesn’t make any significant enhancement in the electrochemical performance of the LiCoPO4.