Sandwich-like reduced graphene oxide wrapped MOF-derived ZnCo2O4–ZnO–C on nickel foam as anodes for high performance lithium ion batteries

Abstract

A sandwich-like structure with reduced graphene oxide (RGO) wrapped MOF-derived ZnCo₂O₄–ZnO–C polyhedrons on nickel foam as an anode for high performance lithium ion batteries (LIBs) is for the first time reported via simply growing MOFs on Ni foam, and wrapping graphene oxide nanosheets on MOFs, and then annealing under a N₂ atmosphere. It should be noted that the MOF-derived porous products are composed of carbon-coated spinel ZnCo₂O₄–ZnO nanoparticle polyhedrons. When tested as anodes for LIBs, the unique RGO/ZnCo₂O₄–ZnO–C/Ni sandwich-structured LIB anodes exhibit superior coulombic efficiency, excellent cycling stability and rate capability. The in situ formed carbon layers outside the ZnCo₂O₄–ZnO act as not only a conductive substrate but also a buffer layer for volume changes. The open pores in ZnCo₂O₄–ZnO–C polyhedrons provide sufficient electrolyte as well as serve as cushion space to further alleviate volume changes. The RGO nanosheets act as a flexible protector to firmly fix polyhedrons on the Ni foam, as well as a conductive substrate to wire up all the polyhedrons. The interconnected carbon layers and two high conductive substrates (RGO and Ni foam) together form an unhindered highway for charge transfer during discharge/charge processes, promising good electrochemical performance.