Preparation and Characterization of LiNi0.5Co0.5O₂ and LiNi0.5Co0.4Al0.1O₂ by Molten Salt Synthesis for Li Ion Batteries

The layer compounds LiNi 0.5 Co 0.5 O 2 and LiNi 0.5 Co 0.4 Al 0.1 O 2 were prepared by using the molten salt of the eutectic mixture LiNO 3 −LiCl at temperatures of 750 and 850 °C in air. They were characterized by X-ray diffraction, Rietveld refinement, SEM, EDAX, chemical analysis, surface area, and density techniques. Cathodic behavior was examined at ambient temperature by cyclic voltammetry, charge−discharge cycling, and impedance spectra in cells with Li−metal as the counter electrode at a current rate of 30 mAg -1 with a lower cutoff voltage of 2.5 V up to 120 cycles. The upper cutoff voltages ranged from 4.2 to 4.5 V. The 10th cycle reversible capacities for LiNi 0.5 Co 0.5 O 2 varied from 131 to 186(±3) mAhg -1 depending on the upper cutoff voltage, but capacity fading occurred ranging from 5 to 18% at the end of 50 or 80 cycles. The Al-doped compound showed a 20th cycle reversible capacity of 146 (±3) mAhg -1 (4.3 V cutoff) which was stable up to 120 cycles. Good rate capability was also observed. Thus, LiNi 0.5 Co 0.4 Al 0.1 O 2 with only 0.4 mol of cobalt is a cheaper and viable alternative to the presently used cathode, LiCoO 2 . Impedance spectra on cells cycled up to 60 cycles with 4.3 V cutoff have been analyzed and interpreted.