Ab initio study of molybdenum sulfo-selenides alloy as a flexible anode for sodium-ion batteries

In the recent times, sodium-ion batteries (SIBs) are exceptionally popular as a cost-effective replacement for lithium-ion batteries (LIBs), particularly for load levelling of renewable energy sources. Using state-of-the-art density functional theory (DFT) calculations, we investigate the alloy of MoS2 and MoSe2 to be used as anode for rechargeable SIBs. We provide atomic level studies of important electrochemical properties of the electrode material in terms of electronic conductivity, voltage profile, specific capacity, sodium ion mobility, and mechanical strength. Our results show that the electrode possess high specific charge capacity of 1036 mA h g(-1) and a low anode potential window of 1.52-0.14 V, leading to high rate capability performance. In addition to high capacity, introduction of selenium also boosts the conductivity of the pristine MoS2 material while not affecting the mechanical strength as well as maintaining the structural stability. We calculate low ion-hopping barrier of 0.035 eV and 0.052 eV for diffusion on the outside surface of Se and S atoms, suggesting fast mobility of Na and hence fast charging/discharging rate. Moreover, MoSSe alloy can withstand strains as high as 25%, depicting ultrahigh flexibility without any structural distortion even at high concentration of Na atoms.