Fig. 6

XRD profiles and electron microscopy images of fully lithiated Si. a XRD spectra of fully lithiated Li–Si alloys for type-A electrodes at 10 mV for depth of discharge (DOD)100, 90, and 80% over 150 cycles. XRD spectra at various delithiation potentials under DOD100% at (b) the 23^rd cycle and (c) the 86^th cycle. In the 23^rd cycle, c-Li_3.75(+δ)Si diffraction peaks disappear only after 550 mV on delithiation, while it does so at 150 mV at the 86^th cycle. d Full width of half maximum (FWHM) of the (332) peak in c-Li_3.75(+δ)Si XRD profiles over 150 cycles for DOD100, 90, and 80%. FWHM for DOD100% saturates near 65^th cycle, while that for DOD90% and 80% continuously increases until the 150^th cycle. Empty squares colored yellow, blue, and purple correspond to fully lithiated electrodes at 10 mV shown in the following electron microscopy images. e–g Bright-field and dark-field TEM images with selected area diffraction pattern (SADP) and index planes shown in inset. The fully lithiated Si in (e) the 3^rd cycle, (f) the 65^th cycle, and (g) the 107^th cycle under DOD100% controls. Scale bars are (e) 200 nm and (f, g) 500 nm. It is obvious that c-Li_3.75(+δ)Si crystals become much smaller in the 65^th and the 107^th cycles, compared to those in the 3^rd cycle, which agrees with the trend seen in (d)