Elevated stability of nickel-rich oxide cathode material with concentration gradient of transition metals via a novel size-controllable calcination method

Consumers are increasingly demanding the range and safety of the electric vehicles. Nickel-rich layered lithium transition-metal oxide cathode material with Ni content exceeding 80% has attracted extensive attention due to its high capacity. To suppress the decrease of cyclic and thermal stability due to the increase of nickel content, LiNi0.87Co0.06Mn0.07O2 particles with transition metal concentration gradient from the interior to the surface are realized. An efficient and low-cost method is proposed involves firstly forming the shell layer with low nickel content by a dry mechanofusion process and subsequently adopting a novel particle size-controllable calcination course. Through which a concentration gradient layer with a thickness of 1 µm is successfully formed, and the particle size of primary particles is effectively controlled at the range of 250–300 nm. The relationship between the calcination conditions, the morphology, particle size of primary particles and the electrochemical performance have been established. Capacity of 211.9 mAh/g and initial coulomb efficiency of 90.29% have been achieved by LiNi0.87Co0.06Mn0.07O2 with superficial transition metal concentration gradient, and the capacity retention rate at 1 C reached 86.1% after 400 cycles in a pouch cell. In addition, the thermal decomposition temperature is elevated from 220 °C to 242 °C, the safety of the Ni-rich material has been also effectively improved.