Revealing the fast reaction kinetics and interfacial behaviors of CuFeS hollow nanorods for durable and high-rate sodium storage.

The synergistic effect of two metallic elements in metal sulfides is regarded as a promising route for constructing advanced anodes for sodium-ion batteries (SIBs). However, the explorations of intricate interactions and structural evolution in host material are often overlooked, which are crucial for the performance optimization. Herein, a bimetallic sulfide CuFeS and FeS/CuS heterostructure with similar hollow nanorods morphology is obtained by regulating sulfuration conditions. Compared to the FeS/CuS heterostructure, the interaction between CuSFe in CuFeS weakens the strength of iron-sulfur bonds, thereby facilitating the kinetics of the sodiation reaction and enabling fast-charging capability. Moreover, the higher adsorption of NaF enables CuFeS to form a thinner solid electrolyte interface film with richer content of inorganic components. Coupled with the presence of stable intermediate phase, CuFeS delivers the excellent electrochemical performances, including a high capacity of 611 mAh/g after 200 cycles at 1 A/g, and 408 mAh/g after 1000 cycles at 30 A/g. Furthermore, CuFeS also demonstrates a remarkable capacity retention of 88 % after 200 cycles at 1 A/g in full-cells. This work highlights the potential of CuFeS in SIBs while elucidating the underlying factors contributing to the exceptional performance of bimetallic sulfides.