Fig. 6: Stability characteristics of electrodes before and after cycling for Na||HESSe cell.

a, b 3D CT (15 × 13.6 × 15 µm3 and 15 × 13.3 × 15 µm3, in x × y × z directions) and Cu WL energy distribution slices at different depths of a pristine and b cycled (3.0 V charged state) for HESSe. SEM images of c HESSe, d LESSe and e CuS after 100 cycles at 1.0 A g−1.