(Invited) In-Situ Microscopy and Spectroscopy Probing of Li Dendrite Nucleation and Growth

Abstract

Lithium (Li) metal has very low standard electrochemical redox potential and very high theoretical specific capacity, making it an ultimate anode material for rechargeable batteries. However, its application has been impeded by the formation of Li whiskers, which not only considerably consumes electrolyte and active Li, but also may lead to short-circuit of the battery. Tackling of these obstacles is limited by the elusive understanding on the intrinsic formation mechanisms of the Li whiskers and their growth behavior under the constraints from the separator. Here, by coupling an atomic force microscopy cantilever into a solid open-cell setup in environmental transmission electron microscopy, we directly captured the nucleation and growth behavior of Li whiskers under elastic constraint that mimics the effect of a separator. We show that Li deposition is initiated by a sluggish nucleation of a single crystalline Li particle with no preferential growth directions. Dramatically, we discovered that carbonate species in the initial solid electrolyte interphase that is very adjacent to the developing Li metal plays a decisive role in the subsequent formation of Li with a whisker morphology. Characteristically, the growing Li whisker, depending on both intrinsic and extrinsic conditions, can yield, buckle, kink, or stop (axial) growth under elastic constraint from the separator. These findings reveal the intrinsic cause and give a clear process on the formation and behavior of dendritic Li under stress, providing the much-needed insights for solving the Li whisker formation from the root cause rather than as currently containing it, and therefore potentially leading to the safe operation of Li metal anode in batteries.