A functionalized porous Al current collector enables high-energy density anode-free Na batteries

Anode-free Na batteries offer the highest possible energy density but suffer from rapid capacity decay resulting mainly from the formation of Na dendrites and large volume change. Here, we design a functionalized porous Al current collector created through template-free electrodeposition and physical separation methods to modulate Na growth behavior. The controlled porous architecture, featuring interconnected ligament-channel networks, reduces structural stress and inhibits dendritic Na formation by lowering local current density and uniformizing ion flux. In addition, the abundant sodiophilic active sites boost reaction kinetics, decrease Na nucleation barrier, and subsequently manipulate homogeneous Na nucleation. Consequently, the porous Al host exhibits high reversibility of dendrite-free Na plating/stripping behavior. A proof-of-concept 4.3 V-class pouch cell achieves an energy density of up to 420.4 watt-hours per kilogram and stable cycling performance with 84.9% capacity retention over 100 cycles under anode-free conditions, providing a pathway for the design of anode-free Na batteries for practical applications.