THIN-FILM LITHIATION STRUCTURAL TRANSFORMATIONS IMAGED IN SITU BY LIQUID CELL TRANSMISSION ELECTRON MICROSCOPY

摘要

Li-ion batteries currently rely on graphite as a host material for lithium intercalation at the negative electrode, but the charge storage capacity is limited with a maximum of one Li atom stored per six C atoms. Alternatively, materials that form solid solution alloys with Li such as Si, Sn, Ge, or Au can exhibit an order of magnitude higher gravimetric charge storage capacity, but the large volume expansion of 200-300% upon lithiation leads to electrode degradation through pulverization and loss of electrical connection. In addition, continued exposure of fresh surfaces to the electrolyte upon expansion causes growth of solid-electrolyte interphase layers by electrolyte reduction which immobilizes lithium and consumes electrolyte. Developing strategies to accommodate the active material’s expansion and contraction requires a detailed understanding of the microstructure evolution upon lithiation and delithiation. While post-mortem examination of disassembled electrodes provides the final picture, the use of in situ imaging techniques can show the dynamic structural transformations that occur in Li alloy host materials at the nanoscale.