SiC Substrate-Enabled Modulation of Li⁺ Ion Intercalation Thermostability in Strained Bilayer Graphene

Two-dimensional (2D) van der Waals (vdW) materials have emerged as vital components in various technological fields. Ion intercalation into vdW materials is a versatile technique for material exfoliation, property induction, and stacking-order manipulation. However, the role of the substrate and its consequential impact on ion intercalation thermodynamics in vdW materials are yet to be well understood. In this work, employing density functional theory (DFT) calculations, we investigate the interplay between the SiC substrate and Li+ ion intercalation in the strained bilayer graphene grown on the SiC (0001) substrate. Our analysis covers five stacking orders (AA, AB, BA, SP, and IM stackings), revealing that the SiC substrate enhances the thermostability of Li+ ion intercalation. This enhancement is attributed to the special sp3-hybrid carbon atoms in the bottom graphene layer. We observed that the SiC substrate promotes selective intercalation with a stacking preference, favoring AA stacking over the other four stackings. Surprisingly, the SiC substrate not only disrupts the crystal symmetry within bilayer graphene, leading to distinctive intercalation behaviors in AB and BA stackings ─absent in free-standing bilayer graphene─but also modulates the Fermi level shift downward by inducing p-type doping to facilitate Li+ ion intercalation. Our study offers a comprehensive understanding of the intricate relationship between substrates and ion intercalation in layered materials, thereby paving the way for tailored applications of layered vdW materials with substrates through ion intercalation.