Rational design of NiCo2S4@MoS2 ball-in-ball heterostructure nanospheres for advanced lithium-sulfur batteries

Abstract

Lithium sulfur battery has a theoretical specific capacity of up to 1600 mA h g−1, which has a significant prospect. However, the shuttle effect of polysulfide, the low conductivity of sulfur and the serious volume change during charging and discharging process hinder the commercial application of lithium-sulfur batteries (LSBs). Here, the flower-like ball-in-ball NiCo2S4@MoS2 heterojunction composites were fabricated as the effective sulfur host in LSBs, which exhibited high specific capacity and durable cyclic life. The NiCo2S4 made up ball-in-ball structure offering more chemisorption sites to limit lithium polysulfide (LiPS) dissolution, and the MoS2 nanosheets grow in the surface of NiCo2S4 sphere to form three dimensional flower structure for accelerating the kinetics of LSBs redox reaction. Additionally, the specific hollow structure also availably alleviated the volume change during charging and discharging. Based on these merits, the NiCo2S4@MoS2 electrode with a sulfur content of 74% possessed an initial specific capacity of 1118 mAh g−1 at 0.1 C, and still had a reversible capacity of 865 mAh g−1 after 300 cycles. Even at a high rate of 5 C, the capacity of 467 mAh g−1 could still be achieved after 500 cycles.