Fig. 3a and b shows the SEM and TEM images of Sn0.92Sb0.08O2.04 nanoparticles, respectively. The particles have a size distribution ranging from 10 to 20 nm in diameter. Fig. 3c and d shows the morphologies of SnSb@C nanoparticles prepared using different glucose to Sn0.92Sb0.08O2.04 weight ratios of 1:1 (sample A) and 2:1 (sample B), respectively. If the weight ratio of glucose to Sn0.92Sb0.08O2.04 is too small (such as 0.5:1), only small nanoparticles are formed with very low yield (as shown in Fig. S1a). If the weight ratio of glucose to Sn0.92Sb0.08O2.04 is too large (such as 4:1), the products aggregate to kinds of large agglomerates (as shown in Fig. S1b). When the weight ratio of glucose to Sn0.92Sb0.08O2.04 is 1:1 (sample A) and 2:1 (sample B), it can be seen that the morphologies of the obtained samples have been changed. Light and dark contrast indicating the SnSb-C core–shell structure is clearly observed in the images. Comparing Fig. 3c and d, it can be found that the particles of sample A show the core–shell structure, but there is aggregation between particles (seen as red-colored cycles in Fig. 3c), while the particles of sample B have a good core–shell structure and there is no obvious aggregation between particles and the particle sizes (seen as red-colored1 arrows in Fig. 3d) are slightly smaller than sample A. It seems to indicate that the different concentration of glucose in the reaction medium has an effect on controlling the growth of particles [30]. Therefore, the size of the as-prepared carbon-coated SnSb alloys is relatively homogenous and the well core–shell structure formed when glucose to Sn0.92Sb0.08O2.04 weight ratio is 2:1.