Lithium stripping: anisotropic evolution and faceting of pits revealed by operando 3-D microscopy

Abstract

A critical challenge that hinders the development of next-generation lithium (Li) metal batteries is the poor reversibility of Li plating and stripping. This study explores the dynamic evolution of Li metal surface morphology during stripping. A platform for operando focus variation microscopy is presented and used to reveal strong anisotropy and faceting in surface pits, which correlates with surface microstructure. Specifically, this study: (1) maps out the dynamic morphological evolution of individual pits in 3-dimensions; (2) demonstrates anisotropic pit expansion in both in-plane and through-plane directions; (3) correlates anisotropy with surface grain boundaries and crystallographic texture; and (4) demonstrates faceted edges in pits, which align within individual grain orientations. The results presented provide greater insight into the fundamental nature of Li stripping reactions and raise new questions about the role of microstructure in reversible cycling of Li metal.