Fig. 6: Calculated free energy for AB- and AA- stacked bilayer graphene intercalated with lithium.

Data for AB- and AA- stacking are shown by black and blue symbols, respectively. Temperature 330 K and \(\Delta \mu=0.4\) eV, as determined experimentally. Labels mark N in the corresponding C_NLiC_N stoichiometries. Bright symbols correspond to Li-ion configurations with hexagonal symmetry; light symbols to non-hexagonal configurations with non-equidistant Li positions such as, e.g., \(\sqrt{21}\times 4\) for C₄₀LiC₄₀, \(\sqrt{13}\times \sqrt{7}\) for C₂₀LiC₂₀. Where several possible configurations were considered for the same stoichiometry (e.g., C₄₂LiC₄₂, C₂₀LiC₂₀, C₁₈LiC₁₈) the hexagonal ion arrangement was always found to have the lowest energy. Dashed lines: guides to the eye connecting data for the hexagonal arrangements. The arrow indicates \({N}_{{{{\rm{Li}}}}}/{N}_{{{{\rm{C}}}}}\) at which the transition from AB to AA stacking is calculated to occur. Source data are provided as a Source Data file.