Fig. 4

Morphological changes of SnO film and SnO NBs with charge/discharge cycling processes. Cross-sectional SEM image of (a) SnO film after 50 cycles and (b) SnO NBs after the first cycle. The insets in b show an HR TEM image and the corresponding FFT image of a hierarchical SnO NB after the first cycle. c SEM image of SnO NBs after 10 cycles, d magnified SEM image of the area marked in c, e cross-sectional SEM image of SnO NBs after 50 cycles, (f) magnified SEM image of the area marked in (e)