Fig. 7.

Ex situ MAS ⁷Li solid-state NMR spectra at various (de)lithiation potentials. a Schematics of various Li–Si local environments as a function of Li concentration in Li–Si alloys. The ⁷Li resonances are highlighted by yellow (10–0 p.p.m., larger Si clusters and extended Si networks), blue (25–10 p.p.m., small Si clusters), pink (6–0 p.p.m., isolated Si⁴⁻ anions including c-Li_3.75Si), and green (0 to −10 p.p.m., overlithiated crystalline phase, c-Li_3.75+δSi). The notations for the Li–Si environments and their correlation with the Li–Si electrochemical processes are also summarized in Supplementary Table 5. The recorded spectra at various Li/Li⁺ potentials over 107 cycles at the probing points under (b) depth of discharge (DOD)100% and (c) DOD90%. The NMR spectra at each potential are linked to the corresponding points in the capacity–voltage profiles. Orange, gray, red, and blue solid lines correspond to the spectra at the 1^st, 23^rd, 65^th, and 107^th cycles, respectively. The spectra for different cycle numbers and different potentials are stacked with constant pitch to show the different processes more clearly