Property Evolution of Al2O3 Coated and Uncoated Si Electrodes: A First Principles Investigation

In order to compare the difference between coated and uncoated Si electrode, the basic material properties of atomic layer deposition ALD-Al2O3 coating and native SiO2 layer on Si are investigated by using density functional theory calculations. These properties include: the open circuit voltage curve with respect to lithium metal, the elastic properties, and Li ion diffusion characteristics in SiO2 and Al2O3 and their lithiated compounds (such as Li4SiO4 and LiAlO2). Results show that lithiation occurs at the voltage above EC (Ethylene Carbonate) decomposition(similar to 0.8V) causing initial irreversible capacity loss. Also, lithiation softens Al2O3 mechanically, while slightly stiffens SiO2. For the Li ion diffusion, SiO2 and Al3O3 have totally different behavior upon lithiation. For SiO2, Li diffuses very fast, but the energy barrier becomes higher as lithiation goes on. When SiO2 is lithiated to Li4SiO4, the diffusion energy barrier becomes lower again. For Al2O3, its intrinsic ionic conductivity is very low, but the Li diffusion energy barrier becomes lower (as low as Li2Si2O5) as lithiation proceeds and LiAlO2 is formed. Therefore, designing ALP coating should target the coating properties after lithiation. (C) 2014 The Electrochemical Society. All rights reserved.