Variation of cathode properties of LiNi0.975M0.025O2 (M = Ga, In and Tl) prepared by the combustion method

LiNi0.975M0.025O2 (M = Ga, In and Tl) were synthesized by the combustion method (by preheating at 400 °C for 30 min in air and then calcining in an O2 stream at 750 °C for 36 h). XRD analyses, SEM observation and measurement of the variation of discharge capacity with the number of cycles were carried out. All the samples had the image structure, and LiNi0.975In0.025O2 contained LiInO2 phase as an impurity. Among these samples, LaNi0.975Ga0.025O2 had the largest first discharge capacity (172.2 mAh g−1) and relatively good cycling performance (discharge capacity 140.3 mAh g−1 at n = 20). For LiNi0.975M0.025O2 (M = Ga, In and Tl), the first discharge capacity decreased with increase in the ionic radius of the substituted element. The variation of cation mixing with the substituted element (decrease in I0 0 3/I1 0 4 and increase in R-factor from M = Ga through M = Tl) is considered to be related to the behavior of the first discharge capacity with the substituted element.