Density Functional Theory Calculations of Alkali Metal (Li, Na, and K) Graphite Intercalation Compounds

First-principles calculations were done to examine the energetics of alkali metal intercalation into graphite. Calculations based on the exchange-correlation functionals that include a nonlocal correlation were found to give reasonable agreement with experiments concerning the crystal structure of graphite and LiC6, binding energy of graphene sheets, and Li intercalation potential. We found that K intercalation from KC8 to KC6 cannot be achieved through electrochemical reactions. We also found that the absence of the stage-I structures for Na graphite intercalation compounds such as NaC6 or NaC8 is linked to a relatively high redox potential of Na/Na+ compared to that of Li/Li+.