Cascade Selenization Regulated the Electronic Structure and Interface Effect of Transition Metal Sulfides for Enhanced Sodium Storage

The utilization of cobalt‐based sulfides is constrained by their inherently low conductivity and slow sodium ion diffusion kinetics. Modifying the electronic configuration and constructing heterostructures are promising strategies to enhance intrinsic conductivity and expedite the sodium ion diffusion process. In this study, heterogeneous nanoparticles of Se‐substituted CoS2/CoSe2, embedded within heteroatom‐modified carbon nanosheet, were synthesized using metal molten salt‐assisted dimensionality reduction alongside concurrent sulfurization and selenization techniques. The incorporation of Se into CoS2 markedly enhances its intrinsic conductivity, thereby significantly improving its rate performance. The elongated Co‐S bonds and the formation of CoSe2 species contribute to the acceleration of dynamics and facilitate the construction of the CoS2/CoSe2 heterointerface. In‐situ Raman spectroscopy, in conjunction with theoretical calculations, has elucidated the sodium storage mechanism of the Se‐CoS2/CoSe2 and the underlying factors contributing to its enhanced performance. The synergistic effects of electronic structure engineering, have resulted in the optimized Se‐CoS2/CoSe2 demonstrating exceptional rate performance, achieving 442 mAh g−1 at 10 A g−1, and a prolonged cycle lifespan, maintaining 409.3 mAh g−1 at 5 A g−1 over 2100 cycles and 262.5 mAh g−1 after 7000 cycles at 10 A g−1. This study presents a viable strategy for integrating electronic structure engineering with interface engineering.