ELECTROCHEMICAL CYCLING AND IMPEDANCE STUDIES OF COMPOUNDS, Li(MMn11/6)O4 (M = Mn1/6, Co1/6, (Co1/12Cr1/12)) PREPARED AT 650℃

摘要

The compounds, Li(MMn11/6)O4 (M=Mn1/6, Co1/6, (Co1/12Cr1/12) were prepared by the polymer precursor route, followed by solid sate reaction at 650℃ for 6 h in air. The as prepared bare and doped compounds were characterized by Rietveld refined X-ray diffraction (XRD), Scanning electron microscopy (SEM), density and Brauner, Emmet and Teller (BET) measurements. Bare and doped samples show a pure spinel phase and without any impurities. SEM studies of the bare and doped compounds show the particle sizes are in the range of 50-100 nm. Cyclic voltammetry and the galvanostatic studies are made in the voltage window of 3.5 to 4.3 V, at room temperature. The compound LiMn2O4 is found to obtain a reversible discharge capacity of 102 (±3) mAh/g at the end of 2nd cycle for 1C rate (assuming 1C=120 mA/g) with a capacity retention of 82 and 75%, between 2 to 500 and 2 to 1000 cycles, respectively. Co-doped LiMn2O4 deliver a reversible capacity of 82 (±3) mAh/g at the end of 1000 cycles, with good capacity retention of 94% at 1C rate. For the high current rate of 5C (600 mA/g), the bare compound showed a reversible discharge capacity of 82 mAh/g at the end of 2nd cycle and a capacity retention of 85% between 2 to 500 cycles. Further cycling studies on doped and impedance studies are discussed.