MC 2 (M = Y, Zr, Nb, and Mo) monolayers containing C 2 dimers: prediction of anode materials for high-performance sodium ion batteries.

Seeking novel high performance anode materials for sodium ion batteries (SIBs) is an attractive theme in developing energy storage devices. In this work, by means of density functional theory computations, we predicted a family of MC 2 (M = Y, Zr, Nb, and Mo) monolayers containing C 2 dimers to be promising anode materials for SIBs. The stability, electronic structure, and adsorption/diffusion/storage behavior of sodium atoms in MC 2 (M = Y, Zr, Nb, and Mo) monolayers were explored. Our computations revealed that Na adsorbed MC 2 (M = Y, Zr, Nb, and Mo) monolayers show metallic characteristics that give rise to excellent electrical conductivity and Na mobility with low activation energies for diffusion (0.21, 0.04, 0.20, and 0.22 eV, respectively) in these materials, indicative of a high charge/discharge rate. In addition, the theoretical capacities of Na-adsorbed on YC 2 , ZrC 2 , NbC 2 , and MoC 2 monolayers are 478, 697, 687, and 675 mA h g -1 , respectively, higher than that of commercial graphite (284 mA h g -1 ), and the open-circuit voltages are moderate (0.11-0.25 V). Our results suggest that MC 2 (M = Y, Zr, Nb, and Mo) monolayers have great potential to serve as anode materials for SIBs.