Probing electrodes at a nanometer scale is challenging but desirable to reveal the structural evolution of materials in electrochemical reactions. Herein, we present an atomic force microscopic method for an in situ analysis of a single Sn nanoparticle during sodiation and desodiation, which is conducted in an aprotic liquid electrolyte akin to a real electrochemical environment of the Na-ion cells. The morphological evolution of different-sized single Sn nanoparticle is visualized during the charge/discharge cycles by using a homemade planar electrode. All of the Sn nanoparticles exhibit a dramatic initial volume expansion of about 420% after sodiation to Na15Sn4. Interestingly, we find that the smaller Sn nanoparticles show a lower rate of irreversible volume change and a better shape maintenance than the larger ones after desodiation. This finding suggests the importance of downsizing in improving the mechanical stability and the cycling performance of the Sn-based anodes in sodium-ion batteries.
Keywords: atomic force microscopy; irreversible volume change; single nanoparticle; sodium-ion batteries; tin.