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Pure Appl. Chem., 2008, Vol. 80, No. 11, pp. 2521-2536

Synthesis and electrochemical studies on surface-modified LiCoVO4 with La2O3 and malonic acid for cathode material of Li-ion cells

George Ting-Kuo Fey, Yung-Da Cho and Pandurangan Muralidharan

Department of Chemical and Materials Engineering, National Central University, Chung-Li, Taiwan 32054 R.O.C.

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.