Gradient-tailored and heterointerface-rich architectures enable superior Li-ion storage performances of GeS2@NiS@N-doped carbon microspheres

The mesoporous compositional gradient nitrogen-doped carbon encapsulated germanium disulfide-nickel sulfide (abbreviated as "GeS2@[email protected]C") microspheres have been synthesized. The Ni3Ge2O5(OH)4 microspheres precursor is firstly prepared by a hydrothermal mineralization process, which transforms to Ge3Ni5 microspheres by high temperature reduction. A thin polydopamine shell protects the microsphere architecture, which is converted into nitrogen-doped carbon layers. The GeS2@[email protected]C microspheres are finally fabricated via a high temperature interdiffusion vulcanization process induced by Kirkendall effect, during which the interdiffusion rate of Ni atoms is much faster than that of Ge atoms leading to the gradual composition changes from the exterior (NiS phase is rich) to the interior (GeS2 phase is rich) throughout a single microsphere. The GeS2@[email protected]C microspheres show unique structural advantage of the abundant heterogeneous interfaces, which accelerates the Li+ diffusion kinetics proved by density functional theory results. Besides, the in-situ XRD analyses reveal a continuous lithiation sequence as the compositional gradient from NiS to GeS2, during which the in-situ generated Ni clusters from NiS construct a continuous and penetrating e− transport channel throughout the microsphere. As a result, the GeS2@[email protected]C microspheres exhibit improved cycling stability and rate capability when employed as anodes for lithium ion batteries.