Anode‐Free Sodium Metal Batteries: Mechanisms, Challenges, and Applications

Abstract The interfacial side reactions involving highly reactive sodium during battery operation will cause irreversible active sodium loss, which could lead to poor Coulombic efficiency, rapid capacity decay, and limited cycling lifespan of sodium metal batteries (SMBs). To tackle these issues, extensive efforts have been devoted to developing anode‐free SMBs (AFSMBs), and favorable progress has been achieved. However, it should be noted that the latest advances in AFSMBs lack a scientific summary from the perspective of interface chemistry behaviors. In this review, the working mechanisms of AFSMBs are elaborately dissected, critical challenges are analyzed, and targeted optimization strategies are proposed, focusing on three pivotal aspects: current collector engineering, electrolyte optimization, and cathode design. Specifically, emphasis is placed on the mechanistic understanding of sodium deposition/stripping behaviors and interphase formation ways. Meanwhile, advanced characterization techniques are mentioned to reveal interface evolution and failure mechanisms of AFSMBs. Finally, future research directions of AFSMBs are proposed to pave the way for developing high‐performance secondary sodium batteries.