Ab initio prediction and characterization of phosphorene-like SiS and SiSe as anode materials for sodium-ion...

In this work, a density functional theory (DFT) based first-principles study is carried out to investigate the potential of phosphorene-like SiS and SiSe monolayers as anode materials for sodium-ion (Na-ion) batteries. Results show that both SiS and SiSe have large adsorption energies towards single Na atom of -0.94 and -0.43eV, owing to the charge transfers from Na to SiS or SiSe. In addition, it is found that the highest Na concentration for both SiS and SiSe is x=1 with the chemical formulas of NaSiS and NaSiSe, corresponding to the high theoretical specific capacities for Na storages of 445.6 and 250.4mAhg^-1, respectively. Moreover, Na diffusions are very fast and show strong directional behaviors on SiS and SiSe monolayers, with the energy barriers of only 0.135 and 0.158eV, lower than those of conventional anode materials for Na-ion batteries such as Na₂Ti₃O₇ (0.19eV) and Na₃Sb (0.21eV). Finally, although SiS and SiSe show semiconducting behaviors, they transform to metallic states after adsorbing Na atoms, indicating enhanced electrical conductivity during battery cycling. Given these advantages, it is expected that both SiS and SiSe monolayers are promising anode materials for Na-ion batteries, and in principle, other Na-based batteries as well.