Multiscale Study of a Synergistic System in Carbon‐Coated Multimetal‐Based Selenides Toward Rapid and Highly Stable Sodium Storage

ABSTRACT The development of sodium‐ion batteries (SIBs) is limited by slow charge transfer kinetics and large material volume changes caused by the large radius of Na + . Leveraging the excellent physicochemical properties and unique heterostructures of metal selenides, ultrafine hetero‐CuFeSe 2 ‐CoSe 2 nanoparticles are in situ wrapped by polyvinylpyrrolidone‐derived carbon (PDC) to successfully synthesize multicomponent composite electrode materials (CuFeSe 2 ‐CoSe 2 @PDC) for SIB anodes. The carbon‐coated trimetallic selenide heterostructure synergistically enhances electronic/ionic conductivity while maintaining exceptional structural stability, thereby significantly improving the reaction kinetics of active materials. In addition, the exceptionally high pseudocapacitive contribution (97% at 1.0 mV s −1 ) plays a pivotal role in achieving high reversible specific capacity, excellent cycling stability, and superior rate capability. Benefiting from the multicomponent synergistic effects, the electrode delivers an exceptional specific capacity of 457.88 mAh g −1 after 1000 cycles at 2 A g −1 , with an ultralow average capacity decay rate of merely 0.0021% per cycle. Density functional theory (DFT) calculations further elucidate that the CuFeSe 2 ‐CoSe 2 heterointerface induces electronic structure reconstruction, and the generated built‐in electric field promotes interfacial electrochemical kinetics. Ex situ X‐ray diffraction (XRD) further revealed the reversible phase transformation reaction mechanism and confirmed the remarkable structural stability of CuFeSe 2 ‐CoSe 2 @PDC. This offers a feasible strategy to design high‐performance electrodes capable of rapid and stable Na + storage.