Structural and electrochemical characterizations of nanostructured olivine LiNi1-xCoxPO4 (x=0 and 0.5) cathode materials for lithium-ion batteries

Abstract

Olivine structured lithium transition metal phosphates are interesting cathode materials for lithium-ion batteries due to their excellent thermal and structural stability. This paper describes the synthesis of nanostructured olivine LiNi1-xCoxPO4 (x = 0 and 0.5) cathode materials were prepared by solid state reaction method. The synthesized materials are characterized by X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and Fourier infrared transform spectra (FTIR) studies. All the X-ray diffraction peaks of both the compounds are indexed and it is found that the samples are well crystallized in orthorhombic olivine structure belonging to the space group Pnma. The crystallite size is calculated from the Scherer's formula and it is found to be 6.918 and 4.818 nm for pure and doped samples respectively. The surface morphology and grain sizes of the materials are investigated through scanning electron microscope. Presence of preferred local cation environment is understood from Fourier transform infrared spectroscopy (FTIR) studies. The assembled lithium cells were electrochemically characterized by charge/discharge and cyclic voltammetry. It is found that the specific capacities of samples with LiNi1-xCoxPO4 (x = 0, 0.5) are about 172.4 mAhg−1 and 173.2 mAhg−1 respectively. The efficiency is slightly improved after cobalt substitution. Based on the above results, the cobalt substituted LiNiPO4 cathode material has been tried as effective substituent.