Suppression of volume expansion in Sn-M (M= Cu, Mn, Ni) alloy anode materials for sodium ion battery

Sn shows high volume expansion corresponding to its high capacity, hindering cycle performance. To resolve the problem, studies are being conducted on alloying metal elements with the Sn anode. For an overall analysis or optimization of various alloying conditions, atomistic simulations are used to investigate the atomic scale structural evolution in Sn anodes during Na infusion. In the present study, we choose Cu, Mn, and Ni as candidate metal elements for alloying, considering the conditions of metal elements. Then, the clustering behavior of metal elements as sodium infuses into Sn-M (M = Cu, Mn, Ni) alloy is investigated using an atomistic simulation. We find that Sn-M alloy is stable in an amorphous solid solution, and as Na atoms infuse, a phase transformation occurs such that M elements are separated out, forming M clusters and a NaxSn amorphous phase, which eventually causes a reduction in volume. Finally, a diffusion simulation is also conducted for Na infusion into spherical Sn-M nanoparticles, to see if the alloying element decreases the Na diffusion rate severely. The comparison of volume reduction and Na infusion rate suggests that Cu is the best alloying element for the Sn base alloy anode materials.