Electrochemical properties of nanostructured SnPx@C/RGO for a high-capacity sodium-ion battery anode

Abstract

Owing to the high theoretical volumetric and gravimetric capacities, tin phosphide (SnPx ) has received great attention as one of the most promising anode materials for sodium ion batteries (SIBs). Nevertheless, SnPx has a low electrical conductivity and undergoes the severe pulverization resulted from a large volume change during sodiation/desodiation process, which leads to rapid decline in the performance. These problems can be solved by tuning nanostructure of the composite materials composed of SnPx and conductive carbon materials. Furthermore, the sodium ion storage of SnPx depends on the compositional ratio of Sn to P because theoretical capacity of phosphorus is about three times higher than metallic tin. In this study, we synthesized hybrid composites composed of size-controlled SnPx nanoparticles covered with thin carbon shell and reduced graphite oxide (RGO) by a facile direct reaction method between liquid phase tin and gas phase phosphorus. Through this method, we could control the Sn/P composition ratio from 1.33 to 0.48 by regulating of cooling rate after reaction and phosphorus partial pressure in a reactor. The SnPx@C/RGO composite with smaller Sn/P ratio (0.48) showed the improved sodium ion storage of ~810 mAh/g, compared to those with larger Sn/P ratio (~1.33).