Pure and Applied Chemistry

Abstract: An inverse spinel LiCoVO₄ cathode material was synthesized by a citric acid-urea polymeric method, calcined at 773 K for 5 h. The synthesized LiCoVO₄ sample was surface-modified with La₂O₃ and/or malonic acid. The composite materials were comprehensively characterized with the aid of various spectroscopic and analytical techniques. X-ray diffraction (XRD) patterns revealed that single-phase crystallinity occurred when they were heated at 773 K for 5 h in air. For the La₂O₃-coated samples, there was no evident signal corresponding to secondary-phase peaks. Fourier transform infrared (FTIR) spectra showed the complete elimination of organic residues, nitrates, and the formation of pure LiCoVO₄ at 773 K. The two strong peaks due to sp² and sp³ carbon bonding in the Raman spectra clearly confirm the presence of carbon coating at the surface of LiCoVO₄ particles. Transmission electron microscopy (TEM) images showed that the 0.5 wt % La₂O₃-coated LiCoVO₄ material calcined with 60 wt % malonic acid was compact with an average thickness of about 15 nm. This composite cathode material also demonstrated the best cell performance with an initial capacity of 71 mAhg^-1 and better thermal stability with lower heat evolution of 35 Jg^-1, and a higher onset temperature of thermal decomposition at 475 K, vs. 176 Jg^-1 and 452 K for the bare LiCoVO₄ sample.