Synthesis of LiNi1−xCoxPO4/C nanocomposite cathode for lithium ion batteries by a combination of aerosol and powder technologies

Abstract

Pure LiNi1−xCoxPO4 (x = 0, 0.2, 0.5, 0.8, 1) was synthesized by spray pyrolysis followed by heat treatment. The X-ray diffraction (XRD) patterns of LiNi1−xCoxPO4 were indexed to olivine structure with a Pnma space group. The peak shift and variation of lattice parameters suggested that LiNi1−xCoxPO4 solid solution was formed. Moreover, LiNi1−xCoxPO4/C (x = 0, 0.2, 0.5, 0.8, 1) nanocomposites were successfully synthesized by a combination of spray pyrolysis and wet ball milling followed by heat treatment. The XRD patterns of all samples were indexed to olivine structure with a Pnma space group. From scanning electron microscopy images, the primary particle sizes of LiNi1−xCoxPO4/C nanocomposites were reduced to the range of approximately 50–100 nm. LiNi0.5Co0.5PO4/C cathode exhibited a higher first discharge capacity and cyclability than those of pure LiNi0.5Co0.5PO4. Cyclic voltammetry data demonstrated that reduction peaks of LiNi0.5Co0.5PO4/C cathode occur at 4.44 V and 4.71 V, which were ascribed to Co3+/Co2+ and Ni3+/Ni2+ reduction couples, respectively. Electrochemical impedance spectroscopy data revealed that the LiNi0.5Co0.5PO4/C cathode had a smaller charge transfer resistance, resulting in a faster redox reaction kinetics for the lithium insertion and extraction, due to reduced particle size and introduced conductive carbon.