Property Evolution of Al₂O₃Coated 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-Al 2 O 3 coating and native SiO 2 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 SiO 2 and Al 2 O 3 and their lithiated compounds (such as Li 4 SiO 4 and LiAlO 2 ). Results show that lithiation occurs at the voltage above EC (Ethylene Carbonate) decomposition(∼0.8V) causing initial irreversible capacity loss. Also, lithiation softens Al 2 O 3 mechanically, while slightly stiffens SiO 2 . For the Li ion diffusion, SiO 2 and Al 2 O 3 have totally different behavior upon lithiation. For SiO 2 , Li diffuses very fast, but the energy barrier becomes higher as lithiation goes on. When SiO 2 is lithiated to Li 4 SiO 4 , the diffusion energy barrier becomes lower again. For Al 2 O 3 , its intrinsic ionic conductivity is very low, but the Li diffusion energy barrier becomes lower (as low as Li 2 Si 2 O 5 ) as lithiation proceeds and LiAlO 2 is formed. Therefore, designing ALD coating should target the coating properties after lithiation.