High-performance LiCoO2 by molten salt (LiNO3:LiCl) synthesis for Li-ion batteries

In an effort to increase and sustain the reversible capacity of LiCoO2 on cycling, LiCoO2 is prepared by using the molten-salt of the eutectic LiNO3-LiCl at temperatures 650-850 degrees C with or without KOH as an oxidizing flux. The compounds are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), chemical analysis, surface area and density techniques. Cathodic behaviour was examined by cyclic voltammetry (CV) and charge-discharge cycling. The 850 degrees C-synthesized LiCoO2, which has excess lithium incorporated in to it, shows a reversible capacity, with similar to 98% coulombic efficiency, of 167 (+/- 2) mAh g(-1) at a specific current of 30 mAg(-1) in the range 2.5-4.4 V up to 80 cycles with no capacity-fading. When cycled to a higher cut-off voltage (4.5 V), a capacity of 192 (+/- 2) mAh g(-1) versus Li is obtained at the fifth cycle, but capacity-fading is observed, viz., similar to 6% after 60 cycles. On the basis of the CV and capacity-voltage profiles, this is attributed to the non-suppression of the hexagonal (H1) <-> (H1-3) structural transition. A similar capacity-fading, i.e., similar to 5-6%, during 5-40 cycles, is also observed in the LiCoO2 prepared at 650 and 750 degrees C when cycled up to only 4.3 V and this is ascribed to the non-suppression of the H1 <-> M <-> H1 phase transitions (M = monoclinic). (c) 2005 Published by Elsevier B.V.