The current status of sodium metal anodes for improved sodium batteries and its future perspectives

Sodium-ion batteries with evident merits in resource abundance and expenditure are emerging as a more suitable alternative to lithium-ion batteries for fulfilling the voracious energy demand of human activities. As the integral component of the battery, the exploration of anode materials suited to the electrochemical system during the last few decades has been never suspended, and the sodium metal anode successfully stands out with its high theoretical capacity and low redox potential. However, a huge gap exists between the direct usage of the sodium metal anode and the large-scale applications, as the uncontrollable sodium dendritic growth during cycling brings about serious concerns (i.e. infinite volume change, unstable solid electrolyte interphase, and safety issues) on battery performance losses. Although a few review articles on high-performance sodium metal anode have been already published, new research on solving the aforementioned challenges is still in progress. Therefore, we herein summarize the recent progress on the high-energy sodium metal anode from four aspects (protective layers, electrolyte additives, three-dimensional framework current collectors, and alloy materials) together with the detailed discussion and analysis in this Perspective. Furthermore, the potential directions and prospects of future research on constructing high-performance sodium metal anodes are also proposed.