Stripping and Plating Behavior of Sodium Metal in Carbonate and Ether Electrolytes

Sodium (Na) stripping is a subsurface process, where sodium (Na) metal is oxidized into Na ions and vice versa during the plating process of cell operation. The morphological/structural changes in the metal following the charge transfer during stripping can largely affect the subsequent plating process. While the reactions and kinetics at the electrode-electrolyte interface are being recognized as the primary factor in limiting the applicable capacity of Na metal anode, a unified framework incorporating a detailed electrochemical study of various electrolyte formulations is still lacking. In this work, we used different types of carbonates (PC, PC: FEC) and ether-based solvents (DME, diglyme, and TEGDME) with NaClO4 and NaPF6 salts to explore the compatibility of Na metal in different liquid electrolyte system. The microscopic images were compared in the context of Na deposition and pitting. The electrolyte composition has a distinctive effect on the evolution of the plated and stripped Na profile, and it was observed that TEGDME for both NaClO4 and NaPF6 salts has severe effects of sodium corrosion, evident by large cavities in the Na metal. Dramatic changes in growth morphological variables, particularly thickness, have a large impact on system viability, affecting the packaging, and thus, identifying the prevalence of the Na deposition or stripping is critically important. The dynamic changes in the voltage profile in a symmetric cell setup were also examined during extended cycles to understand the reaction and mass transport limitation in different electrolyte solvents. As the stripping and plating processes are indirect proof of cell aging, the observed behavior of Na metal-salt-solvent interaction in this work will help to highlight the potential for developing a better Na metal system with long term electrochemical performance.