Synthesis of yolk-shell structured microspheres consisting of heterogeneous nickel cobalt selenide@nickel cobalt selenite core-shell nanospheres and their application of anode materials for sodium-ion batteries

Recently, heterostructure interfaced construction by binary metal selenide or metal oxide/metal selenide configuration has been attracting attention as anodes for sodium-ion batteries (SIBs). Especially, modification strategies such as formation of core-shell structure consisting of heterointerface can be a solution to resolve the issue of metal selenide electrodes. In this paper, new multicomponent metal compounds with heterointerface structure are firstly designed and suggested as anode for SIBs. The yolk-shell microsphere consisting of heterogeneous NiCo selenide@NiCo selenite core-shell nanospheres was prepared by spray pyrolysis and facile selenization and subsequently partial oxidation processes. NiCo selenide nanocrystals, which constitute the yolkshell structure, are partially transformed into the NiCo selenide@NiCo selenite phase during the oxidation process. Notably, this process induces the nanoscale Kirkendall effect, leading to the transformation of the metal selenide nanocrystals into a hollow nanosphere morphology. As a result, the material adopts a hollow nanosphere structure with a NiCo selenide@NiCo selenite core-shell configuration. To the best of our knowledge, metal selenide@metal selenite core-shell configuration with hollow nanosphere is proposed for the first time. Heterointerface as well as yolk-shell structure consisting of hollow nanospheres showed synergistic effect for efficient and excellent sodium ion storage.