SiC Substrate-Enabled\nModulation of Li<sup>+</sup> Ion Intercalation\nThermostability in Strained Bilayer Graphene

Two-dimensional\n(2D) van der Waals (vdW) materials have emerged\nas vital components in various technological fields. Ion intercalation\ninto vdW materials is a versatile technique for material exfoliation,\nproperty induction, and stacking-order manipulation. However, the\nrole of the substrate and its consequential impact on ion intercalation\nthermodynamics in vdW materials are yet to be well understood. In\nthis work, employing density functional theory (DFT) calculations,\nwe investigate the interplay between the SiC substrate and Li<sup>+</sup> ion intercalation in the strained bilayer graphene grown\non the SiC (0001) substrate. Our analysis covers five stacking orders\n(AA, AB, BA, SP, and IM stackings), revealing that the SiC substrate\nenhances the thermostability of Li<sup>+</sup> ion intercalation.\nThis enhancement is attributed to the special sp<sup>3</sup>-hybrid\ncarbon atoms in the bottom graphene layer. We observed that the SiC\nsubstrate promotes selective intercalation with a stacking preference,\nfavoring AA stacking over the other four stackings. Surprisingly,\nthe SiC substrate not only disrupts the crystal symmetry within bilayer\ngraphene, leading to distinctive intercalation behaviors in AB and\nBA stackings absent in free-standing bilayer graphenebut\nalso modulates the Fermi level shift downward by inducing p-type doping\nto facilitate Li<sup>+</sup> ion intercalation. Our study offers a\ncomprehensive understanding of the intricate relationship between\nsubstrates and ion intercalation in layered materials, thereby paving\nthe way for tailored applications of layered vdW materials with substrates\nthrough ion intercalation.