Density Functional Theory Calculations of Lithium Adsorption and Insertion to Defect-Free and Defective Graphene

Density functional theory calculations with periodic boundary conditions were performed to clarify the interaction between lithium atoms and a graphene sheet. Three types of graphene sheets defect-free, containing carbon vacancies V-Cn (n = 1, 2, 3, 4, 6, 10, 13, 16, and 24), and their hydrogen-terminated carbon vacancies were examined in this study. We found that a lithium atom inserted into bare carbon vacancy V-Cn (n >= 3) is more stable than that in bulk lithium metal and that it is trapped by the vacancy. On the other hand, a lithium atom inserted into the hydrogen-terminated carbon vacancies is less stable than that in bulk metal. These results suggest that the electrochemical in-plane insertion of lithium ions into the bare carbon vacancies is possible, whereas the insertion into the hydrogen-terminated vacancies is unlikely because the precipitation of lithium metal is energetically more favorable.