Simulation on the Initial Stage of Sodium–Graphite Intercalation Using First-Principles Calculation

Abstract

Na–C intercalation is one of the major causes for cathode deterioration in reduction cells, in which the initial stage is important for understanding the microstructure evolution and developing strategy for cathode improvement. In this paper, a single sodium atom adsorbed on a single carbon layer for assembling one of multiple layers of graphite, has been investigated using first principles density functional theory (DFT). Results show that the center of a carbon ring is the preferred site for sodium adsorption at the initial stage of Na–C contact. When the single layer structure vary from ($\sqrt 7$ × $\sqrt 7$) to (5 × 5) in pattern, adsorption energy of sodium–carbon system has a parabolic trend and the supercell of Na/C = 1/14 has the lowest absolute value of adsorption energy in this paper due to the influences of both charge transfer and Coulomb interaction, while other geometry properties change monotonically as sodium coverage increasing. Carbon p and sodium s and p states can all contribute to the density of states at Fermi level. The Fermi energy of graphene increases due to charge transfer form sodium to graphene.