Yolk-shell FeSe2@CoSe2/FeSe2 heterojunction as anode materials for sodium-ion batteries with high rate capability and stability

Sodium-ion batteries are promising candidates for large-scale grid storage systems and other applications. Their foremost advantage derives from superior environmental credentials, enhanced safety as well as lower raw material costs than lithium-ion batteries. It is still challenging to explore desirable anode material. In this study, FeSe2@CoSe2/FeSe2, with a yolk-shell structure was prepared by ion exchange and selenisation. The FeSe2@CoSe2/FeSe2 prepared as anode material for sodium-ion batteries exhibits excellent rate capability due to the synergistic effect of bimetallic selenides and the interfacial effect of the heterostructure. Moreover, it delivers high performance (510 mAh g−1 at 0.2 A g−1), superior rate capability (90% retention at 5 A g−1), and good long-time cycling stability (78% capacity retention after 1800 cycles at a high current density of 2 A g−1). The optimized sodium-ion full cell with FeSe2@CoSe2/FeSe2 as the anode and Na3V2(PO4)3 as the cathode still demonstrates excellent performance. Namely, a capacity of 272 mAh g−1 (at 1 A g−1) within the operating voltage from 1 to 3.8 V can be obtained. This work illustrates the potential of bimetallic selenides with heterostructures for performance enhancement of sodium-ion batteries.