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 R3¯m 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.