Structural Stability of Li[sub 1−x]Ni[sub 0.85]Co[sub 0.15]O[sub 2] and Li[sub 1−x]Ni[sub 0.85]Co[sub 0.12]Al[sub 0.03]O[sub 2] Cathodes at Elevated Temperatures

Layered LiNi 0.85 Co 0.15 O 2 and LiNi 0.85 Co 0.12 Al 0.03 O 2 oxides have been synthesized by a gel method and a hydroxide precursor method. The LiNi 0.85 Co 0.12 Al 0.03 O 2 oxide prepared by the hydroxide precursor route exhibits a reversible capacity of around 170 mAh/g with excellent cyclability. With an objective to evaluate the structural stability of nickel-based layered oxides, the variations in the lattice parameters of charged Li 1 − x Ni 0.85 Co 0.15 O 2 and Li 1 − x Ni 0.85 Co 0.12 Al 0.03 O 2 cathodes with temperature have been investigated. The change in lattice parameters have been monitored by ( i ) heating the charged cathodes at various temperatures in air after the first charge and after 20 cycles, ( ii ) heating at various temperatures the cycled coin cells in the charged state without opening, and ( iii ) cycling the cells at various temperatures. The experiments reveal a decrease in the c / a ratio with increasing temperature ( T > 50 ° C ) due to a migration of the nickel ions from the nickel planes to the lithium planes. The change in the c / a ratio is more pronounced during the initial number of cycles and it becomes less pronounced as the cathodes are cycled.