Efficient Sodium Storage in Rolled‐Up Amorphous Si Nanomembranes

Alloying-type materials are promising anodes for high-performance sodium-ion batteries (SIBs) because of their high capacities and low Na-ion insertion potentials. However, the typical candidates, such as P, Sn, Sb, and Pb, suffer from severe volume changes (≈293-487%) during the electrochemical reactions, leading to inferior cycling performances. Here, a high-rate and ultrastable alloying-type anode based on the rolled-up amorphous Si nanomembranes is demonstrated. The rolled-up amorphous Si nanomembranes show a very small volume change during the sodiation/desodiation processes and deliver an excellent rate capability and ultralong cycle life up to 2000 cycles with 85% capacity retention. The structural evolution and pseudocapacitance contribution are investigated by using the ex situ characterization techniques combined with kinetics analysis. Furthermore, the mechanism of efficient sodium-ion storage in amorphous Si is kinetically analyzed through an illustrative atomic structure with dangling bonds, offering a new perspective on understanding the sodium storage behavior. These results suggest that nanostructured amorphous Si is a promising anode material for high-performance SIBs.