Wood's Alloy Film Anode with Fast and Durable Na+ Storage

Abstract Alloy‐type materials are highly promising anode candidates for sodium‐ion batteries (SIBs)/sodium‐ion capacitors (SICs) because of their high theoretical capacity and low redox potentials. However, the intrinsic defects of alloying materials, including poor cycling stability and slow reaction kinetics, limit their development. In this study, a thin Wood's alloy (WA) film is fabricated on Cu foil (denoted as WA@Cu) through a one‐step blade method due to the low‐melting property of WA. This WA@Cu film provides a discharge specific gravimetric/volumetric capacity of 383.6/3350.8 mAh g −1 /mAh cm −3 at 0.2 A g −1 , a high initial coulombic efficiency of 89.07% and a long cycle life over 15 000 cycles at 5.0 A g −1 . Even at high mass loadings (7.6–14.3 mg cm −2 ), this WA@Cu electrode can still cycle 250 times. In situ and ex situ characterization techniques and theoretical calculations reveal that its rapid and durable Na + storage mechanism is related to the spontaneous formation of a 3D porous network structure upon cycling. This 3D interconnected porous structure effectively alleviates volume expansion, relieves local stress concentration, and promotes Na + transport. An energy‐dense and high‐power SIC based on this WA@Cu electrode is further fabricated. This work offers a new choice for the development of high‐performance anode materials for SIBs/SICs.