Electrochemical properties of LiNi1−yCoyO2 cathode materials synthesized from different starting materials by the solid-state reaction method

LiNi1−yCoyO2 (y = 0.1, 0.3 and 0.5) were synthesized by the solid-state reaction method at 750 °C, 800 °C and 850 °C from LiOH·H2O, NiO and Co3O4 and from Li2CO3, NiO and Co3O4 as the starting materials. The physical and electrochemical properties of the synthesized LiNi1−yCoyO2 were compared. The synthesized LiNi1−yCoyO2 has the α-NaFeO2 structure of the rhombohedral system (space group; R3¯m). The particle size increases, on the whole, as the synthesis temperature increases or as the Co content increases. The particle sizes of the LiNi1−yCoyO2 specimens synthesized from Li2CO3, NiO and Co3O4 at all three temperatures are larger than those of the specimens synthesized from LiOH·H2O, NiO and Co3O4 for all of the compositions. Among the samples synthesized from LiOH·H2O, NiO and Co3O4, LiNi0.5Co0.5O2 synthesized at 800 °C has the largest first discharge capacity (174.3 mAh/g) and relatively good cycling performance. Among the samples synthesized from Li2CO3, NiO and Co3O4, LiNi0.7Co0.3O2 synthesized at 750 °C has the best cycling performance (capacity fading rate 0.3 mAh/g cycle) and a relatively large first discharge capacity. The former has a larger value of Imax/B, a larger grain size and a smaller specific surface area than the latter.