Multifunctional High‐Entropy Alloy Nanolayer Toward Long‐Life Anode‐Free Sodium Metal Battery

Abstract Anode‐free sodium metal batteries (AFSMBs) hold great promise due to high energy density and low cost. Unfortunately, their practical applications are hindered by poor cycling stability, which is attributed to Na dendrite growth and inferior Na plating/stripping reversibility on conventional sodiophobic current collectors. Here, a thin high‐entropy alloy (HEA, NbMoTaWV) interfacial layer composed of densely packed nanoplates is constructed on commercial aluminum foil (NbMoTaWV@Al) for AFSMBs. The enhanced sodiophilicity of the HEA greatly reduces Na nucleation barrier with low nucleation overpotential. Simultaneously, abundant active sites of the HEA can boost interfacial reaction kinetics and guide uniform Na deposition. Furthermore, plentiful HEA nanoplates can homogenize electric field distribution and decrease the local current density. Benefiting from the advantageous properties of NbMoTaWV@Al, outstanding electrochemical performances, including an average Coulombic efficiency of 99.5% over 1000 cycles at 2 mA cm −2 /2 mAh cm −2 in asymmetric cells, alongside a small overpotential (10 mV at 1 mA cm −2 ) and a long lifespan of 2500 cycles in symmetric cells, are achieved. More impressively, the anode‐free NbMoTaWV@Al||Na 3 V 2 (PO 4 ) 3 batteries display superior cycling stability over 300 cycles. This work presents an efficient method of employing multifunctional HEA materials to manipulate the interfacial properties of current collector for high‐performance AFSMBs.