Recent developments and insights into the understanding of Na metal anodes for Na-metal batteries

Rechargeable Na-based battery systems, including Na-ion batteries, room temperature Na-S, Na-O-2, Na-CO2, and all-solid-state Na metal batteries, have attracted significant attention due to the high energy density, abundance, low cost, and suitable redox potential of Na metal. However, the Na metal anode faces several challenges, including: (1) the formation of Na dendrites and short circuiting; (2) low Coulombic efficiency (CE) and poor cycling performance; and (3) an infinite volume change due to its hostless nature. Furthermore, the issues associated with Na metal anodes have also been noticed in practical Na metal batteries (NMBs). In recent years, the importance of the Na metal anode has been highlighted and many studies have provided potential solutions to address the issues of its use. This review article focuses on the recent developments of Na metal anodes, including insight into the fundamental understanding of its electrochemical processes, novel characterization methods, approaches for protecting the anode and future perspectives. Our review will accelerate further improvement in the characterization and application of Na metal anodes for next-generation NMB systems.