In Situ observation of Tin Oxide (SnO₂) Lithium Battery Nanowires in a Transmission Electron Microscope, TEM

J. Y. Huang, L. Zhong, C. M. Wang, J. P. Sullivan, W. Xu, L. Q. Zhang, S. X. Mao, N. S. Hudak, X. H. Liu, A.Subramanian, H. Y. Fan, L. Qi, A. Kushima and J. Li, “In situ observation of the electrochemical lithiation of a single SnO2 nanowire electrode,” Science 330 (2010) 1515.

Tin Oxide (SnO₂) Lithium Battery Nanowires

We report the creation of a nanoscale electrochemical device inside a TEM (transmission electron microscope)—consisting of a single tin dioxide (SnO₂) lithium battery nanowire anode, an ionic liquid electrolyte, and a bulk lithium cobalt dioxide (LiCoO₂) cathode—and the in situ observation in the TEM of the lithiation of the SnO₂ nanowire during electrochemical charging. Upon charging, a reaction front propagated progressively along the nanowire, causing the nanowire to swell, elongate, and spiral. The reaction front is a “Medusa zone” containing a high density of mobile dislocations, which are continuously nucleated and absorbed at the moving front. This dislocation cloud indicates large in-plane misfit stresses and is a structural precursor to electrochemically driven solid-state amorphization. Because lithiation-induced volume expansion, plasticity, and pulverization of electrode materials, as seen in the TEM, are the major mechanical effects that plague the performance and lifetime of high-capacity anodes in lithium-ion batteries, our observations provide important mechanistic insight for the design of advanced batteries.

An in-situ TEM movie showing the microstructural evolution of a SnO₂ lithium battery nanowire anode as it was charged at -3.5 V vs. LiCoO₂. As the reaction front passed by, the former SnO₂ nanowire diameter expanded, and the length elongated. In the meantime, crystalline SnO₂ was converted to nanocrystalline Sn and LixSn dispersed in an amorphous Li₂O matrix. The video was recorded at 2 frame/s and played at 33×.

An in-situ TEM movie showing that dislocations in the nanowire are continuously emitted from the reaction front. As the reaction front or the high density of dislocations passed by, the crystalline contrast changed to a gray amorphous contrast, and the diameter and length of the lithium battery nanowire increased. The video was recorded at 2 frame/s and played at 30×.