Recent advances in in situ electrochemical transmission X-ray microscopy (EC-TXM), with its unique ability to provide simultaneous temporally and spatially resolved information as well as electrochemical parameters, enable exploration of the underlying physics of the electrochemical reactions that occur at the surface and inside of secondary energy storage devices during cycling [4,5]. Here, we focus the direct visualization of the propagation of Li dendrites at short-circuit condition using in situ EC-TXM. After the short-circuit, we follow three-dimensional morphological and microstructural changes of Li dendrites to explore relationships between electrochemical parameters and failure mechanisms during cycling. We further characterize the structural evolution of Li dendrites using in situ X-ray diffraction.
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 We gratefully acknowledge funding supports from the BP Carbon Mitigation Initiative.