Effect of Al dopant on the structure, electrical and dielectric properties of olivine LiNi0·5Co0·5PO4 cathode material

Abstract

LiNi0·5Co0.5-xAlxPO4 (x = 0.0, 0.05, 0.1 and 0.15) cathode materials were synthesized by using solid-state reaction method. The effect of the substitution of some amount of Al for Co site on the structure of these materials was investigated by using x-ray powder diffraction (XRD), scanning electron microscope (SEM) and Fourier transform infrared (FT-IR) spectroscopy The electrical and the electrochemical performances of the synthesized materials were also investigated by using complex impedance spectroscopy and galvanostatic charge-discharge test. The XRD analysis confirmed that LiNi0·5Co0.5-xAlxPO4 cathode materials are well crystallized and belong to the Pmna space group with olivine structure. Surface morphology showed that all the prepared samples have a porous structure. The FT-IR spectra showed the formation of strong absorption bands typical for olivine crystal structure. The DC conductivity (σdc), ac conductivity (σac) and dielectric permittivity (ε’) of all synthesized samples were estimated as a function of frequency, temperature, and composition. LiNi0.5Co0.4Al0.1PO4 cathode exhibited the highest electrical conductivity of 7.06 × 10−9 S/cm. The initial discharge capacity of the highly conductive LiNi0·5Co0·4Al0·1PO4 cathode was found to be 46.1 mAhg−1 and after 10 cycles, it delivered 38.2 mAh.g−1 of discharge capacity, which was 82.9% of its initial capacity. Considering the large charge-discharge potential window used (2.25–4.8 V), LiNi0·5Co0·4Al0·1PO4 cathode exhibited good discharge specific capacity and cyclic performance.