In-situ construction of vacancies and schottky junctions in nickel-iron selenide within N-graphene porous matrix for enhanced sodium/potassium storage

Abstract

The exploration of suitable anode materials to overcome key issues of electrode volume fluctuation and sluggish electronic/ionic transport dynamics caused by the large radius of sodium/potassium ions is an urgent need for energy storage. Herein, a heterogenetic nickel-iron selenide containing vacancies and schottky junctions within N-graphene porous matrix to realize external and internal charge transport is constructed via a one-pot in-situ carbonization and selenization route. In the composite, the iron selenide possessing metallic property acts as the conductor incorporated with nickel selenide semiconductor for constructing schottky junctions and vacancies to induce internal charge transfer and transport of the active material, and the N-graphene not only enhance the interparticle conductivity by bridging the selenides, but also relieve the volume fluctuation and keep integrity without agglomeration of nanocrystals. Profiting from the synergistic effect, the material exhibits boosted electrochemical properties for sodium (264 mA h g−1 after 1000 cycles at 1.0 A g−1) and potassium (115 mA h g−1 after 500 cycles at 0.5 A g−1) storage. And the thorough understanding of electrochemical mechanism on the raised performance is explicitly interpreted by combining ex-situ characterization results and density functional theoretical calculations.