Research Progress in Anode‐Free Sodium Metal Batteries

Abstract Anode‐free batteries, as an emerging battery technology, have attracted significant research interest due to their ultrahigh theoretical energy density, enhanced safety, and simplified manufacturing. However, the development of anode‐free sodium metal batteries (AFSMBs) is largely hindered by the uncontrolled sodium deposition behavior, resulting in poor cycling stability and low coulombic efficiency. This review summarizes the state‐of‐art progress of AFSMBs with a focus on anode interfacial engineering and electrolyte optimization strategies for mitigating sodium loss during cycling. Links between adverse sodium deposition behavior at interfaces and the performance degradation of AFSMBs are established to decode their failure mechanisms. The essential role of controlled sodium nucleation and stable SEI formation in enabling uniform sodium deposition is also intensively discussed. Recent advances in interfacial engineering and electrolyte design are presented, including 3D current collector architectures and the development of solid‐state electrolytes. Furthermore, the critical importance of in situ characterization techniques for probing fundamental mechanisms is specially accounted. Finally, key research challenges and opportunities as well as some perspectives to develop next‐generation high‐performance AFSMBs are outlined.