Structures and formation energies of Li_xC₆ (x=1-3) and its homologues for lithium rechargeable batteries

Using first principles density functional theory the formation energies of various binary compounds of lithium graphite and its homologues were calculated. Lithium and graphite react to form Li₁C₆ (+141 mV) but not form LiC₄ (-143 mV), LiC₃ (-247 mV) and LiC ₂ (-529 mV) because they are less stable than lithium metal itself. Properties of structure and reaction potentials of C₅B, C ₅N and B₃N₃ materials as iso-structural graphite were studied. Boron and nitrogen substituted graphite and boron-nitrogen material as a iso-electronic structured graphitic material have longer graphene layer spacing than that of graphite. The layer spacing of Li_xC₆, Li_xC₅B, Li_xC ₅N materials increased until to x=1, and then decreased until to x=2 and 3. Nevertheless Li_xB₃N₃ has opposite tendency of layer spacing variation. Among various lithium compositions of Li_xC₅B, Li_xC₅N and Li _xB₃N₃, reaction potentials of Li _xC₅B (x=1-3) and Li_xC₅ (x=1) from total energy analyses have positive values against lithium deposition.