Lithium intercalated bilayer graphene has been investigated using first-principles density functional theory calculations. Results show that there exist AB and AA stacking sequences for bilayer graphene in which the latter is more favorable for the Li storage and the former will evolve into the latter with the intercalation of Li ions. The relationship between the interlayer distance of two graphene sheets and the intercalated capacity of Li ions is discussed. It is found that structural defect is identified to store Li ions more favorably than pristine bilayer graphene and an isolated C atom vacancy in bilayer graphene can capture three Li ions between two graphene sheets.
Structural and magnetic properties of LiNi0.5Mn1.5O4 and LiNi0.5Mn1.5O4-δ are investigated using densityfunctional theory calculations.Results indicate that nonstoichiometric LiNi0.5Mn1.5O4-δ and stoichiometric LiNi0.5Mn1.5O4 exhibit two different structures,i.e.,the face-centred cubic（Fd-3m） and primitive,or simple,cubic （P4332） space groups,respectively.It is found that the magnetic ground state of LiNi0.5Mn1.5O4（P4332 and Fd-3m） is a ferrimagnetic state in which the Ni and Mn sublattices are ferromagnetically ordered along the[110]direction whereas they are antiferromagnetic with respect to each other.We demonstrate that it is the presence of an O-vacancy in LiNi0.5Mn1.5O4-δ with the Fd-3m space group that results in its superior electronic conductivity compared with LiNi0.5Mn1.5O4 with the P4332 space group.
