LiNiO2 and LiNi0.975Ga0.025O2 samples were synthesized by the combustion method. The starting materials, in desired proportions, were dissolved in distilled water and mixed with urea by a magnetic stirrer. The mixture was calcined at 750 oC for 36 h in an O2 stream after preheating at 400 oC for 30 min in air. The phase transitions during charging and discharging and electrochemical performances of the synthesized samples were then investigated. The dQ/|dV| vs. voltage curves, where Q is the charge capacity and V is the voltage, for the charge and discharge of LiNiO2 and LiNi0.975Ga0.025O2 at n (number of cycles) = 1 and n = 2 exhibit four peaks, respectively, indicating four phase transitions from a hexagonal structure (H1) to a monoclinic structure (M), from the M to a second hexagonal structure (H2), from the H2 to H2 and a third hexagonal structure (H3), and from the H2 + H3 to H3 or vice versa. LiNi0.975Ga0.025O2 had a larger first discharge capacity of 166 mA h/g than LiNiO2. It showed a cycling performance, which is not bad, with a discharge capacity degradation rate of 0.76 mA h/g/cycle from n = 1 to n = 50. LiNiO2 had a smaller first discharge capacity of 158 mA h/g but a better cycling performance than LiNi0.975Ga0.025O2 with a discharge capacity degradation rate of 0.45 mA h/g/cycle from n = 1 to n = 50. The electrochemical properties of LiNi0.975Ga0.025O2 prepared by the combustion method were compared with those of the sample prepared by the solid-state reaction method.

Keywords: LiNi1-yMyO2 (M = Ni or Ga), Combustion method, Phase transitions, Discharge capacity, Cycling performance.