In situ imaging the dynamics of sodium metal deposition and stripping

Sodium (Na) metal batteries (SMBs) are potential "beyond lithium (Li)" energy storage technology. However, uncontrollable Na dendrite growth hinders the practical application of SMBs. The dynamics for Na dendrite plating/stripping are still unclear, which affects the development of a uniform Na deposition and stripping strategy. Herein, in situ imaging of the dynamics of Na deposition and stripping was conducted using a nano-electrochemical device in an advanced aberration corrected environmental transmission electron microscope (ETEM). Dodecahedron shaped Na nanocrystals with {110} exposed surfaces were formed during plating. During stripping, Na atoms were extracted layer-by-layer (LBL) along the {110} planes, which switched to the {112} planes once the extraction encountered the corner of the dodecahedra. Density functional theory (DFT) calculations indicate that the crystallography of Na deposition and stripping was controlled by a minimum energy path or Wulff's law, which requires high mass flux to distribute the newly deposited Na. In situ imaging of Na metal deposition and stripping provides new understanding of the Na dendrite dynamics, which may have important implications to develop strategies to suppress Na dendrite growth.