KCu 4 S 3 /CuS Nanosheet Fabricated by a One‐Step Molten Salt Method for Enhancing the Rate Capability of Sodium‐Ion Batteries

ABSTRACT Sodium‐ion batteries (SIBs) are constrained by critical issues such as the volume expansion of electrode materials, insufficient rate and cycling performance. To address these issues, a two‐dimensional KCu 4 S 3 /CuS nanosheet is designed and fabricated via a simple one‐step molten salt method. The obtained material delivers a high reversible specific capacity of 508.39 mAh g −1 at 0.1 A g −1 , and more than 88.5% of the initial capacity is retained even at a high current density of 10.0 A g −1 . Under a full‐cell configuration with a Na 3 V 3 (PO 4 ) 3 cathode, the prepared material still achieves a reversible specific capacity of 94.45 mAh g −1 (based on the mass of anode active material) after 500 cycles at 5.0 A g −1 . The superior rate capability and cycle stability of the obtained material originate from the synergistic effect between KCu 4 S 3 and CuS, coupled with the confinement effect of the in situ formed amorphous carbon, which collectively enhances Na + transport kinetics and effectively buffers volume variation. This work provides a simple and effective strategy for designing high‐performance anode materials for SIBs.