Construction of N-doped C@MoS2 heteroshell with the yolk of Sn nanoparticles as high-performance anodes for sodium-ion batteries

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Herein, we demonstrate the reasonable design and preparation of yolk-heteroshell Sn@N-doped C@MoS2 nanospheres as anode materials in sodium-ion battery. Through an effective multi-step strategy, Sn nanoparticles are encapsulated in N-doped C nanocage surrounded by ultra-thin MoS2 nanosheets to form Sn@N-doped C@MoS2 nanospheres. In this novel structure, Sn nanoparticles with high theoretical capacity improve the space utilization inside the heteroshell; the N-doped carbon nanocage as the skeleton not only inhibits the mutual accumulation of Sn and MoS2, but also improves conductivity; the outer MoS2 ultra-thin sheets can consolidate C@MoS2 heteroshell, provide numerous active sites and favor the fast diffusion of Na+/e-. Notably, the combination of carbon nanocage and MoS2 sheets in the yolk-heteroshell structure can effectually buffer the volume expansion of Sn nanoyolks and reinforce C@MoS2 heteroshell while reducing the carbon content. Therefore, the yolk-heteroshell structure plays a crucial role in enhanced reversible capacity and cyclic stability of Sn@N-doped C@MoS2 nanospheres, which activates their sodium storage potential. The yolk-heteroshell Sn@N-doped C@MoS2 nanospheres exhibit high reversible capacity of 488.4 mAh g−1 at 0.1 A g−1 after 300 cycles and long-cycle stability of 350.6 mAh g−1 at 0.5 A g−1 after 500 cycles. Moreover, their full cell delivers a stable reversible discharge capacity of about 80.1 mAh g−1 after 30 cycles at 0.5 C. This work provides a feasible yolk-heteroshell strategy for Sn-based composite nanomaterials.