In Situ Transmission Electron Microscopy Observation of Microstructure and Phase Evolution in a SnO2Nanowire during Lithium Intercalation

Abstract

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. Science2010, 330, 1515). A key question to be addressed is the lithiation behavior of the nanowire when it is fully soaked into the electrolyte (Chiang Science2010, 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 ↔ Li_xSn + Li_yO, 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 Li_xSn phase possesses a spherical morphology and is embedded into the amorphous Li_yO matrix, indicating a simultaneous partitioning and coarsening of Li_xSn 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.