Fe₃O₄@S nanoparticles embedded/coated on the multi-wall carbon nanotubes for rechargeable lithium batteries

In the present study, Fe₃O₄@S-CNTs-1, Fe₃O₄@S-CNTs-2 and Fe₃O₄@S-CNTs-3 were prepared via one-pot hydrothermal approach. The core–shell Fe₃O₄@S structures (20–30 nm) are embedded/coated on the oxidized CNTs, inhibiting the huge volume expansion effect of active materials during the cycling process. The Fe₃O₄@S-CNTs-2 cathode presented an initial discharge of 986 mAhg⁻¹ (0.2 C) and gradually decreased to 503 mAhg⁻¹ after 200 cycles, exhibiting the best cycling performance among the prepared hybrid materials. Even at a high current density of 1 C, the Fe₃O₄@S-CNTs-2 cathode still exhibited a discharge capacity of 914 mAhg⁻¹, and maintains a high capacity (466 mAhg⁻¹) after 400 cycles. The Coulombic efficiencies of the synthesized Fe₃O₄@S-CNTs hybrid materials always are 99%, indicating they could effectively diminish the shuttle effects of polysulfide Li₂S_n (2 < n < 8) intermediates in the cycling process. As for the rate performance of Fe₃O₄@S-CNTs hybrid materials, the capacity still can reach up to ∼400 mAhg⁻¹ at a high discharge rate of 5 C. The synergy between the Fe₃O₄@S nanoparticles and oxidized CNTs in the Fe₃O₄@S-CNTs cathode endows the electrode with good electrical conductivity, structural stability and high charge capacity thus providing excellent electrochemical performance.