Interface and structure engineering of bimetallic selenides toward high-performance sodium-ion half/full batteries

Transition metal selenides are widely explored as promising anodes for sodium-ion batteries (SIBs) because of their high theoretical capacity. However, rapid capacity decay caused by the structural collapse during cycling greatly hampers their applications in SIBs. Herein, we report a synergistic engineering of interface and structure to synthesize CoSe2–MoSe2 yolk-shell spheres. Such exquisite boundary architecture is beneficial to improving the electrochemical kinetics. Meanwhile, the yolk-shell structure further modulates the mechanical stress for stable performance. As expected, the CoSe2–MoSe2 yolk-shell spheres deliver a high capacity of 466 mAh g−1 after 1000 cycles at the ultrahigh rate of 10 A g−1. The sodium storage mechanism of the CoSe2–MoSe2 yolk-shell spheres is investigated by kinetic tests and first-principles calculations. Coupled with a Na3V2(PO4)2O2F cathode, the as-constructed full batteries show a remarkable energy density of 133 Wh kg−1, promoting the development of high-energy density energy storage devices.