Scalable Synthesis of Hollow β-SiC/Si Anodes via Selective Thermal Oxidation for Lithium-Ion Batteries.

Silicon for anodes in lithium-ion batteries has received much attention owing to its superior specific capacity. There has been a rapid increase of research related to void engineering to address the silicon failure mechanism stemming from the massive volume change during (dis)charging in the past decade. Nevertheless, conventional synthetic methods require complex synthetic procedures and toxic reagents to form a void space, so they have an obvious limitation to reach practical application. Here, we introduce SiCx consisting of nanocrystallite Si embedded in the inactive matrix of β-SiC to fabricate various types of void structures using thermal etching with a scalable one-pot CVD method. The structural features of SiCx make the carbonaceous template possible to be etched selectively without Si oxidation at high temperature with an air atmosphere. Furthermore, bottom-up gas phase synthesis of SiCx ensures atomically identical structural features (e.g., homogeneously distributed Si and β-SiC) regardless of different types of sacrificial templates. For these reasons, various types of SiCx hollow structures having shells, tubes, and sheets can be synthesized by simply employing different morphologies of the carbon template. As a result, the morphological effect of different hollow structures can be deeply investigated as well as the free volume effect originating from void engineering from both a electrochemical and computational point of view. In terms of selective thermal oxidation, the SiCx hollow shell achieves a much higher initial Coulombic efficiency (>89%) than that of the Si hollow shell (65%) because of its nonoxidative property originating from structural characteristics of SiCx during thermal etching. Moreover, the findings based on the clearly observed different electrochemical features between half-cell and full-cell configuration give insight into further Si anode research.