Figure 2: Lithiation-induced structure and morphology evolutions.

(a) XRD spectra of synthesized electrodes before and after 90 or 850 cycles at 1.12 C (the inorganic SEI was removed by washing in ethanol and methanol, then dipping in water for around 2 days), red stars representing the patterns from the Cu foil. (b,c) SEM images of synthesized electrodes before cycling. (d–g) SEM and TEM images of electrodes after 90 cycles at 1.12 C. The red dashed squares in d indicate the cracks in the SEI layers, and the thick region of the non-uniform SEI layer as indicated by the red dashed lines in e is around 50 nm. SEM images in f,g show the 90 cycled electrodes after inorganic SEI removal. The red dotted circles in g indicate the coalesced pores. (h–k) SEM and TEM images of electrodes after 850 cycles at the same rate. The thinner SEI layer in h,i is measured to be around 15 nm. SEM images in j,k show the 850 cycled electrodes after inorganic SEI removal. The red arrows indicate the reduced diffusion length of flower-like nanosheets. Scale bar, 200 nm (b,d,f,j), 100 nm (c,g,h,k), 50 nm (e) and 20 nm (i).