Hollow spheres of solid solution Fe7Ni3S11/CN as advanced anode materials for sodium ion batteries

Owing to high theoretical capacity, transition metal sulfide have been widely studied as promising electrode materials. However, the sluggish kinetics and structural instability caused by high expansion rate limit its electrochemical properties. To solve these problems, in our work, a bimetallic solid solution of Fe7Ni3S11 nanoparticles confined with nitrogen doped carbon (CN) was synthesized by simple one-pot hydrothermal method with post-annealing. The hierarchy structure with Fe7Ni3S11 nanoparticles wrapped with CN can greatly enhance structural stability and fast electrode kinetics. As an anode of sodium ion batteries (SIBs), Fe7Ni3S11/CN exhibits an outstandingly high reversible specific capacity of 567 mAh.g(-1) at 0.2 A.g(-1), and maintains a capacity of 477 mAh.g(-1) after 900 cycles at 2 A.g(-1) with capacity retention rate 90 %. Even at the current density of 6 A.g(-1) for 5000 cycles, it delivers a capacity of 320 mAh.g(-1). Further, a SIBs pairing Fe7Ni3S11/CN anode with Na3V2(PO4)(3)/C cathode has been assembled, delivering a long durable ability for 1000 cycles. This work fabricates a promising solid solution material of Fe7Ni3S11/CN as anode for SIBs with excellent sodium storage capability.