Figure 5
Li conversion of FeF2, as monitored in real time. (a) Schematic of the electrochemical cell used for the in situ TEM measurements. (b) Time-lapse images from a collection of particles that react with Li-ions coming from the lower right. The lithiation proceeds immediately in region (I) but is delayed and absent in regions (II) and (III), respectively. Scale bar is 10 nm. (c) Morphological evolution of a single FeF2 nanoparticle, revealing the rapid formation of the ultrafine (sub-nanometric) Fe particles on the surface, followed by the gradual formation of larger ones (1–3 nm) within the domains of the original FeF2 particle (arrows used to identify specific Fe particles). Scale bar is 10 nm. (d, up) Lattice image of Fe particles converted from a single FeF2 particle (top) along the [−111] zone axis, according to the FFT pattern (inset). (d, down) Intensity profiles of the FFT patterns (bottom) of the Fe lattice in the near-surface region (red circle) and central region (blue circle). Scale bar is 2 nm. Reproduced with permission.47
