Morphology-Tuned NiCo2O4-Coated 3D Graphene Rrchitectures As Binder-Free Electrode for Lithium Ion Battery

Abstract

In recent decades, lithium ion batteries (LIBs) have been considered as the most effective and practical technology products for portable electronic devices because of their flexibility, high energy density and long lifespan. Nanostructured transition metal oxides have been intensively studied as one of the most promising candidates for LIBs because of their high theoretical capacities (500-1000 mAh g-1), good reversible conversion, and low cost. However, in general, poor cycling performance and low electrical conductivity have hindered their practical application. Recently, 3D graphene synthesized by chemical vapor deposition (CVD) method has been studied extensively and used as a binder-free electrode in energy storage devices because of its excellent electron conductivity as current collector and high stability in electrolyte, but the application of 3D graphene as free-standing electrode is still limited due to its weak mechanical strength. In this work, nanostructured NiCo2O4 is directly grown on the surface of three-dimensional graphene-coated nickel foam (3D-GNF) by a facile electrodeposition technique and subsequent annealing. The resulting NiCo2O4 possesses a distinct flower or sheet morphology tuned by potential or current variation electrodeposition, which is used as a binder-free lithium ion battery anode for the first time. Both samples exhibit high lithium storage capacity profiting from unique binder-free electrode structures. The flower-type NiCo2O4 demonstrates high reversible discharge capacity (1459 mAh g–1 at 200 mA g–1) and excellent cyclability with around 71% retention of the reversible capacity after 60 cycles, which are superior to sheet-type NiCo2O4. Such superb performance can be attributed to high volume utilization efficiency with unique morphological character, a well-preserved connection of active materials to the current collector, a short lithium ion diffusion path, and fast electrolyte transfer in binder-free NiCo2O4-coated 3D graphene structure. The simple preparation process and easily controllable morphology make binder-free NiCo2O4/3D-GNF hybrid a potential material for commercial application.