Realizing the Synergy of Interface and Dual-Defect Engineering for Molybdenum Disulfide Enables Efficient Sodium-Ion Storage

Engineering-rich electrocatalyst defects play a critical role in greatly promoting the charge storage/transfer capability of an energy storage/conversion system. Here, an ingenious and effective two-step strategy was used to synthesize a bimetallic sulfide/oxide composite with a coaxial carbon coating, starting from mixing well-dispersed MoO₃ nanobelts and Co-PAA compound, followed by a selective etching process. The simultaneous formation of dual defects of interlayer defect and sulfur-rich vacancies as well as MoO₂/MoS_2-x/CoS heterojunctions noticeably enhances both electron transfer and ion diffusion kinetics. The ultrathin carbon protective layer on the surface of the composite ensures its high conductivity and excellent structural stability. The composite electrode shows a high reversible capacity (158.3 mAh g^-1 at 10 A g^-1 after 4000 cycles) and outstanding long-cycle stability (0.04% per cycle over 2100 cycles at 20 A g^-1). A full cell based on MoO₂/MoS_2-x/CoS@N, S-C anode, and Na₃V₂(PO₄)₃ cathode can maintain a reversible capacity of 128.1 mAh g^-1 after 600 cycles at 1 A g^-1, surpassing that based on MoO₂/MoS₂ and is very comparable in performance with the state-of-the-art Na-ion full cells. Moreover, density functional theory (DFT) calculations, electrochemical kinetics analysis, and in situ Raman and ex-situ X-ray diffraction characterization were carried out to elucidate the involved scientific mechanisms of sodium storage.