Fracture of nanostructured Sn/C anodes during Li-insertion

Sn/C nanocomposites, in the form of Sn or SnO2 islands attached on carbon surfaces, provide a high initial capacity when used as anodes in rechargeable Li-ion batteries. Upon Li-insertion, however, the Sn undergoes significant volume changes which result in fracture and, hence, a fade in capacity. In the present study a detailed electron microscopy analysis was used for the first time to document the fracture that occurred throughout the Li-insertion and de-insertion process. Particularly, scanning and transmission (SEM&TEM) electron microscopy was performed on four different Sn/C nanocomposites, before and after, electrochemical cycling. Analysis of the Sn particle size distribution showed that the greatest amount of fracture occurred during the first cycle. It was concluded that both the particle volume average and the area fraction of the as prepared Sn or SnO2 islands must be kept at low values in order to minimize fracture and, therefore, retain a stable capacity. A simple empirical expression was, hence, presented to relate the capacity with the initial microstructure.