Yung-Da Cho

Pyrolytic carbons from acid/base-treated rice husk as lithium-insertion anode materials*

The effects of hydrochloric acid and sodium hydroxide as leachants on the lithium-insertion properties of pyrolytic carbons prepared from rice husk are presented. All the disordered carbonaceous products had interlayer spacings (d002) of more than 3.7 Å, with values decreasing with an increase in the concentration of the leachant. The values of the H/C ratio and the R-parameter, the reciprocal of which is a measure of the number of non-parallel single layers of carbon, also diminished with an increase in the concentration of NaOH. An increase in the alkali concentration was found to improve the porosity of the carbons, as evidenced by the Brunauer–Emmett–Teller (BET) surface area data. An interaction of these factors determines the observed capacities of the carbon products. The highest insertion and deinsertion capacities were observed with the carbon obtained from rice husk treated with 0.3 M NaOH, the values being 819 and 463 mAh/g, respectively.

Synthesis and electrochemical studies on surface-modified LiCoVO 4 with La 2 O 3 and malonic acid for cathode material of Li-ion cells

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.