The effect of edge termination on Li⁺ ion adsorption of pristine and defected graphene sheets

Graphene-based nanomaterials have attracted great attention for energy storage application in supercapacitors and batteries, along with challenges and perspectives in the exciting field; however, the Li ion batteries with long cycling stability remain a major impediment. In order to enhance the Li⁺ ion adsorption, we employ density functional theory to investigate the adsorption of Li⁺ ion with hydrogen-, fluorine-, chlorine- and bromine-terminated pristine sheet and the corresponding Stone–Thrower–Wales and divacancy defect-incorporated graphene sheet. Our results reveal that fluorine termination enhances Li⁺ ion adsorption compared to H- and other halogen-terminated graphene sheets. On the other hand, Li⁺ ion adsorption energy is increased on introducing the fluorine termination in both pristine and defected graphene sheets, while Li⁺ ion adsorption is more in the divacancy-defected graphene. From the density of states analysis, the Fermi level shows 1.9 eV shift toward the valence band for fluorine termination in both pristine and defected graphene sheets. Fluorine termination is shown to have a significant variation in the valence band than the other halogen atoms, and hence, it offers efficient material energy conversion and storage.