Advantages of Ge anode for Na-ion batteries: Ge vs. Si and Sn

The sodiation properties of alloy-type anode materials (Si, Ge, and Sn) have been evaluated in terms of electrochemical energy storage using first-principles molecular dynamics calculations. We report that Ge can deliver reasonably good performance in all aspects of sodium storage capability, mechanical stability, and ion conductivity, when compared with Si and Sn. The Ge anode: (1) has a strong thermodynamic driving force for sodiation that is comparable to that of Sn and much stronger than that of Si, (2) exhibits moderate volume expansion and bulk modulus upon sodiation that are superior to those of Sn, and (3) allows fast Na ion conductivity that is comparable to that of Sn and is faster by three orders of magnitude than that of Si. Our study suggests that among the group 14 elements, Ge is fairly promising as an anode material for Na-ion batteries.