Enhancement of Electrochemical Activity of Ni-rich LiNi 0.8 Mn 0.1 Co 0.1 O 2 by Precisely Controlled Al 2 O 3 Nanocoatings via Atomic Layer Deposition

Abstract

Ni-rich layered oxides Li(NixCoyMnz)O2 (x + y + z = 1) have been extensively studied in recent times owing to their high capacity and low cost and can possibly replace LiCoO2 in the near future. However, these layered oxides suffer from problems related to the capacity fading, thermal stability, and safety at high voltages. In this study, we use surface coating as a strategy to improve the thermal stability at higher voltages. The uniform and conformal Al2O3 coating on prefabricated electrodes using atomic layer deposition significantly prevented surface degradation over prolonged cycling. Initial capacity of 190, 199, 188 and 166 mAh g is obtained for pristine, 2, 5 and 10 cycles of ALD coated samples at 0.2C and maintains 145, 158, 151 and 130 mAh g for high current rate of 2C in room temperature. The two-cycle Al2O3 modified cathode retained 75% of its capacity after 500 cycles at 5C with 0.05% capacity decay per cycle, compared with 46.5% retention for a pristine electrode, at an elevated temperature. Despite the insulating nature of the Al2O3 coating, a thin layer is sufficient to improve the capacity retention at a high temperature. The Al2O3 coating can prevent the detrimental surface reactions at a high temperature. Thus, the morphology of the active material is well-maintained even after extensive cycling, whereas the bare electrode undergoes severe degradation.