Anode-free sodium metal batteries: Current developments, strategies, and perspectives

Anode-free sodium metal batteries (AFSMBs) with high energy density, high safety, and low cost are considered as one promising alternative for future energy storage systems. However, there are some key challenges such as the formation and growth of Na dendrite, poor stability of solid electrolyte interphase, and limited Na source at the cathodes that result in low Coulombic efficiency and limited cycle life, hindering the practical application of AFSMBs. This review presents the current advancements and potential development directions of AFSMBs. Firstly, the intrinsic advantages and key challenges of AFSMBs are summarized and introduced in brief. Further, the main design strategies for extending the cycle life of AFSMBs on current collector modification, electrolyte design, and cathode presodiation are systematically discussed. Finally, we present the perspectives on the future development of AFSMBs and hope to shed new light on practical applications of AFSMBs.