Effect of Al2O3 Coating on Stabilizing LiNi0.4Mn0.4Co0.2O2 Cathodes

Using atomic layer deposition of Al 2 O 3 coating, improved high-voltage cycling stability has been demonstrated for the layered nickel–manganese–cobalt pseudoternary oxide, LiNi 0.4 Mn 0.4 Co 0.2 O 2 . To understand the effect of the Al 2 O 3 coating, we have utilized electrochemical impedance spectroscopy, operando synchrotron-based X-ray diffraction, and operando X-ray absorption near edge fine structure spectroscopy to characterize the structure and chemistry evolution of the LiNi 0.4 Mn 0.4 Co 0.2 O 2 cathode during cycling. Using this combination of techniques, we show that the Al 2 O 3 coating successfully mitigates the strong side reactions of the active material with the electrolyte at higher voltages (>4.4 V), without restricting the uptake and release of Li ions. The impact of the Al 2 O 3 coating is also revealed at beginning of lithium deintercalation, with an observed delay in the evolution of oxidation and coordination environment for the Co and Mn ions in the coated electrode due to protection of the surface. This protection prevents the competing side reactions of the electrolyte with the highly active Ni oxide sites, promoting charge compensation via the oxidation of Ni and enabling high-voltage cycling stability.