Recent Trends in Artificial SEI Layers for Controlling Dendrite Formation and Enhancing Cycle Life: Toward Stable and Durable Sodium Metal Batteries

The growing demand for sustainable energy storage solutions has stimulated extensive research efforts on sodium metal batteries (SMBs), as a promising alternative storage device to lithium-based systems. SMBs provide advantages over high theoretical capacity and cost-effectiveness, as well as widely available sodium resources, which effectively address the critical limitations associated with the scarcity and high cost of lithium. However, the development of SMBs is hindered by several challenges such as nonuniform sodium ion deposition, dendrite formation, and unstable solid electrolyte interphase (SEI) layers, which lead to poor cycle life and safety concerns. This review provides a comprehensive analysis of the fundamental challenges associated with sodium metal anodes, focusing on the mechanisms of sodium dendrite growth and SEI layer formation. The need for several types of artificial SEI layers and corresponding formation strategies, highlighting their advantages in preventing dendrite formation, is also explored. Furthermore, this review emphasizes the role of advanced characterization techniques, particularly using in situ and cryogenic tools, in elucidating the working mechanisms of sodium metal anodes. Overall, this work aims to provide in-depth insights into the critical bottlenecks and prospective solutions, offering a forward-looking perspective on the advancement of sodium metal battery technologies.