In Situ Transmission Electron Microscopy Observation of Microstructure and Phase Evolution in a SnO2 Nanowire during Lithium Intercalation

Recently we have reported structural transformation features of SnO2 upon initial charging using a configuration that leads to the sequential lithiation of SnO2 nanowire from one end to the other (Huang et al. Science 2010, 330,1515). A key question to be addressed is the lithiation behavior of the nanowire when it is fully soaked into the electrolyte (Chiang Science 2010, 330, 1485). This Letter documents the structural characteristics of SnO2 upon initial charging based on a battery assembled with a single nanowire anode, which is fully soaked (immersed) into an ionic liquid based electrolyte using in situ transmission electron microscopy. It has been observed that following the initial charging the nanowire retained a wire shape, although highly distorted. The originally straight wire is characterized by a zigzag structure following the phase transformation, indicating that during the phase transformation of SnO2 + Li <-> LixSn + LiyO, the nanowire was subjected to severe deformation, as similarly observed for the case when the SnO2 was charged sequentially from one end to the other. Transmission electron microscopy imaging revealed that the LixSn phase possesses a spherical morphology and is embedded into the amorphous LiyO matrix, indicating a simultaneous partitioning and coarsening of LixSn through Sn and Li diffusion in the amorphous matrix accompanied the phase transformation. The presently observed composite configuration gives detailed information on the structural change and how this change takes place on nanometer scale.