Structures and Formation Energies of LixC6 (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 LiC2 (-529 mV) because they are less stable than lithium metal itself. Properties of structure and reaction potentials of C5B, C5N 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 LixC6, LixC5B, LixC5N materials increased until to x=1, and then decreased until to x=2 and 3. Nevertheless LixB3N3 has opposite tendency of layer spacing variation. Among various lithium compositions of LixC5B, LixC5N and LixB3N3, reaction potentials of LixC5B (x=1-3) and LixC5(x=1) from total energy analyses have positive values against lithium deposition.