(520d) Can Phosphorus-Doped Graphene be a Good Anode for Na-Ion Batteries?: A First-Principles Study

Secondary energy storage technologies based on sodium ions are an important emerging alternative to lithium ion batteries (LIBs). Sodium is less expensive than lithium, with its supplies being much wider and more democratically distributed throughout the globe. There are fundamental physical differences between Na and Li, and it is clear the knowledge available from extensive research on LIBs does not translate to sodium. However, the understanding of Na-based systems is at their infancy, and their complexities are just beginning to be understood. In this talk, we theoretically investigated the possibility of using phosphorus-doped (P-doped) graphene as an anode material in sodium ion batteries (NIBs). We reveal some fundamental physical properties of sodium adsorption on P-doped graphene by calculating formation and adsorption energies, voltage vs. capacity curves, migration for Na transport, and electron density of states and mobility. Our calculations suggest that Na adsorption on the same side of protrudent P is the preferred configuration for application in NIBs. This particular configuration possesses very large Na capacity (~582 mAh/g). More importantly, Na has to cross a diffusion barrier (~0.3 eV) and it diffuses in a zigzag path on the P-doped structures due to the presence of protrudent P with larger atomic size compared with the size of a carbon. We will also present electronic movements and accumulations during sodiation. Though carrier mobility may be not as fast as in metals or pristine graphene because P-doped graphene with Na adsorbed on it becomes a semiconductor, the calculated carrier mobility is still significantly large with the order of 10³ to 10⁵ cm²/V/s. Lastly, we will discuss the guidelines for the efficient design of P-doped graphene as a promising anode for NIBs.