Tin Metal Improves the Lithiation Kinetics of High-Capacity Silicon Anodes

Si-based anodes present a great promise for high energy density lithium-ion batteries. However, its commercialization is largely hindered by a grand challenge of a rapid capacity fade. Here, we demonstrate excellent cycling stability on a Si-Sn thin film electrode that outperforms pure Si or Sn counterpart under the similar conditions. Combined with the first-principles calculations, in situ transmission electron microscopy studies reveal a reduced volume expansion, increased conductivity, as well as dynamic rearrangement upon lithiation of the Si-Sn film. We attribute the improved lithiation kinetics to the formation of a conductive matrix that comprises a mosaic of nanostructured Sn, Li_ySn (specifically, Li₇Sn₂ develops around the lithiation potential of Si), and Li_xSi. This work provides an important advance in understanding the lithiation mechanism of Si-based anodes for next-generation lithium-ion batteries.