Effect of Al₂O₃ Coating on Stabilizing\nLiNi_0.4Mn_0.4Co_0.2O₂ Cathodes

Abstract

Using atomic layer deposition of\nAl₂O₃ coating,\nimproved high-voltage cycling stability has been demonstrated for\nthe layered nickel–manganese–cobalt pseudoternary oxide,\nLiNi_0.4Mn_0.4Co_0.2O₂. To\nunderstand the effect of the Al₂O₃ coating,\nwe have utilized electrochemical impedance spectroscopy, operando\nsynchrotron-based X-ray diffraction, and operando X-ray absorption\nnear edge fine structure spectroscopy to characterize the structure\nand chemistry evolution of the LiNi_0.4Mn_0.4Co_0.2O₂ cathode during cycling. Using this combination\nof techniques, we show that the Al₂O₃ coating\nsuccessfully mitigates the strong side reactions of the active material\nwith the electrolyte at higher voltages (>4.4 V), without restricting\nthe uptake and release of Li ions. The impact of the Al₂O₃ coating is also revealed at beginning of lithium deintercalation,\nwith an observed delay in the evolution of oxidation and coordination\nenvironment for the Co and Mn ions in the coated electrode due to\nprotection of the surface. This protection prevents the competing\nside reactions of the electrolyte with the highly active Ni oxide\nsites, promoting charge compensation via the oxidation of Ni and enabling\nhigh-voltage cycling stability.