Mechanistic Origin of the High Performance of Yolk@Shell BiS@N-Doped Carbon Nanowire Electrodes.

High-performance lithium-ion batteries are commonly built with heterogeneous composite electrodes that combine multiple active components for serving various electrochemical and structural functions. Engineering these heterogeneous composite electrodes toward drastically improved battery performance is hinged on a fundamental understanding of the mechanisms of multiple active components and their synergy or trade-off effects. Herein, we report a rational design, fabrication, and understanding of yolk@shell BiS@N-doped mesoporous carbon (C) composite anode, consisting of a BiS nanowire (NW) core within a hollow space surrounded by a thin shell of N-doped mesoporous C. This composite anode exhibits desirable rate performance and long cycle stability (700 cycles, 501 mAhg at 1.0 Ag, 85% capacity retention). By in situ transmission electron microscopy (TEM), X-ray diffraction, and NMR experiments and computational modeling, we elucidate the dominant mechanisms of the phase transformation, structural evolution, and lithiation kinetics of the BiS NWs anode. Our combined in situ TEM experiments and finite element simulations reveal that the hollow space between the BiS NWs core and carbon shell can effectively accommodate the lithiation-induced expansion of BiS NWs without cracking C shells. This work demonstrates an effective strategy of engineering the yolk@shell-architectured anodes and also sheds light onto harnessing the complex multistep reactions in metal sulfides to enable high-performance lithium-ion batteries.