Kinetics of Electrodeposition and Dissolution in Sodium Anodes: Interplay of Na Deposit and Its Solid-Electrolyte Interphase

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Sodium (Na) anodes hold significant potential to meet the growing demand for high-energy-density electrochemical energy storage and an alternative to lithium metals. Achieving long-lasting stability at the metal-electrolyte interface is crucial for the development of emerging sodium metal-based electrochemical energy storage technologies. Currently, fundamental knowledges about the deposition and stripping processes of Na metal anodes remain lacking. These processes typically involve uncontrolled dendritic growth and the formation of a solid electrolyte interphase (SEI) that does not effectively protect the metal from the electrolyte. To better understand the relationship between Na deposits and SEI, we employed advanced synchrotron X-ray characterization techniques, including X-ray nanotomography, grazing-incidence wide-angle X-ray scattering (GIWAXS), and soft X-ray spectroscopy (sXAS). These techniques are complementary: X-ray nanotomography reveals morphological changes, GIWAXS provides insights into crystal structures, and sXAS offers detailed chemical information. Together, they enable a comprehensive understanding of the underlying mechanisms. Additionally, operando GIWAXS was used to monitor the evolution of Na deposits and their SEI in real time. Our results indicate that the wettability of current collectors (Te-Cu: sodiophilic vs. Cu: sodiophobic) significantly influences both the crystallographic orientation of Na deposits, affecting film morphology and internal porosity, and the distribution of SEI components. Specifically, sodium fluoride (NaF) is more prevalent in the SEI formed on Te−Cu collectors, while sodium hydride (NaH) and sodium hydroxide (NaOH) dominate on baseline Cu collectors[1]. Overall, this multimodal approach provides valuable insights into the mechanisms of Na deposition and dissolution, offering a pathway to control the reaction and realize practical applications. Reference: [1] Lo, Chang-An, et al. "Interdependence of Support Wettability‐Electrodeposition Rate‐Sodium Metal Anode and SEI Microstructure." Angewandte Chemie (2024): e202412550.

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