Carbothermal synthesis, spectral and magnetic characterization and Li-cyclability of the Mo-cluster compounds, LiYMo3O8 and Mn2Mo3O8

The molybdenum cluster compounds, LiYMo3O8 and Mn2Mo3O8 are prepared by the carbothermal reduction method and characterized by various techniques. The FT-IR at ambient temperature (RT), and Raman spectra at various temperatures (78-450 K) are reported for the first time and results are interpreted. Magnetic studies on Mn2Mo3O8 in the temperature range, 10-350 K confirm that it is ferrimagnetic, with T-C = 39 K. Magnetic hysteresis and magnetization data at various fields and temperatures are presented. The Li-cyclability is investigated by galvanostatic cycling in the voltage range. 0.005-3.0V vs. Li at 30 mA/g (0.08 C). LiYMo3O8 shows a total first-discharge capacity of 305 +/- 5 mAh/g whereas the first-charge capacity is only 180 mAh/g at RT. However, both values increased systematically with an increase in the cycle number and yielded a reversible capacity of 385 5 mAh/g at the end of 120th cycle. At 50 degrees C, the reversible capacity is 418 +/- 5 mAh/g at the 60th cycle. The coulombic efficiency ranges from 94% to 98%. The Li-cyclability behavior of Mn2Mo3O8 is entirely different from that of LiYMo3O8. The total first-discharge and charge capacities are 710 +/- 5 and 565 +/- 5 mAh/g, but drastic capacity-fading occurs during cycling. The reversible capacity at the end of 50th cycle is only 205 +/- 5 mAh/g. Plausible reaction mechanisms are proposed and discussed based on the galavanostatic cycling, cyclic voltammetry, ex situ XRD, ex situ TEM and impedance spectral data. (C) 2009 Published by Elsevier Ltd.