  Li and Na attachment to free tetracyanoethylene (TCNE) molecules and TCNE
adsorbed on doped graphene is studied using density functional theory. While
TCNE is adsorbed only weakly on ideal graphene, we identified a configuration
in which TCNE is chemisorbed on Al-doped graphene via molecule C atom and a
surface oxygen atom. Up to four (five) Li and Na atoms can be stored on both
free (adsorbed) TCNE with binding energies stronger than cohesive energies of
the Li and Na metals. When storing up to three atoms per molecule, it should be
possible to avoid reduction of common battery electrolytes. TCNE immobilized on
a conducting graphene-based substrate could therefore become an efficient anode
material for organic Li and Na ion batteries. Importantly, there is no
significant difference either in specific capacity (per unit mass of material
excluding Li/Na) nor in voltage between Li and Na storage, which makes this
kind of approach very promising for post-Li storage in general.
