EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Sodium-ion batteries development has gained momentum due to the high abundance of its raw material in the earth's crust, combined with their low cost as compared to resources required for Li-ion batteries. However, due to the large ionic radius of Na as compared to Li, the former intercalation in some of the well-developed Li-ion anode materials (e.g. Si, Ge, graphite) becomes difficult. The anticipated sodiation capacities for Si, Ge and Sn are 957, 369 and 857 mAh g-1 respectively. However, crystalline Si and Ge struggles to activate in Na-ion battery due to the sluggish solid-state diffusion of Na ion in these structures. To overcome this issue, strategies involve the use of amorphous thin films, which tend to activate but at the expense of active material exfoliation from the current collector resulting in poor capacity retention.
In this work, we have investigated the use of 1D SixGe1-x (X=0.25,0.50,0.75) alloy nanowires in Na-ion batteries. The strategy involves the synthesis of SiGe alloy NWs by solvent vapor growth method, followed by amorphization in a Li-ion battery. This amorphization process allows the material to become activated for Na-ion intercalation. This study presents successful activation of SiGe amorphous NW alloy, with a-Si0.5Ge0.5 delivering 250 mAh g-1 as compared to a-Ge delivering only 107 mAh g-1 after 100 cycles at 50 mA g-1. The a-Si NWs failed to activate, suggesting poor Na-ion diffusivity even in the Li-induced amorphous state. The incorporation of Ge in SiGe alloy helped improve Na diffusivity while presence of Si helped in limiting volume expansion which led to the exfoliation of active material from the current collector in pure a-Ge.