Blade-Type Reaction Front in Micrometer-sized Germanium Particles during Lithiation.

To investigate the lithium transport mechanism in micrometer-sized germanium (Ge) particles, in situ Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM) was used to monitor the structural evolution of individual Ge particles during lithiation. Our results show that there are two types of reaction fronts during lithiation, representing the differences of reactions on the surface and in bulk. The cross-sectional SEM images and transmission electron microscopy characterizations show that the interface between amorphous LixGe and Ge has a wedge shape due to the higher Li transport rate on the surface of the particle. The blade-type reaction front is formed at the interface of the amorphous LixGe and crystalline Ge, and is attributed to the large strain at the interface.