Revealing Li growth modes using X-ray nano-tomography

To pave way for application of Li-metal anodes in high energy density batteries the evolution of the 3D structures formed during charging needs accurate characterization inside working cells. The growth of porous, weakly connected structures is directly linked to the poor cycle life of Li-metal batteries. Here, we present the first time-resolved analysis of the lithium metal structural evolution in 3D with sub-micron spatial resolution using in situ X-ray nano-tomography. This enables the growth mechanisms of entangled lithium morphologies to be studied both qualitatively and quantitatively. We identify distinct growth modes of needle-like and sheet-like structures, where segments are elongated at the tip, base, kinks or edges simultaneously with minimal coarsening. Different growth modes, and the transition between them, are linked to local current density variations and SEI evolution, highlighting time resolved 3D morphological characterization as an avenue to understand the mechanisms of Li deposition.