Hierarchical Porous Ni/NiO Nanoflowers with Adjustable Ni As Anode for Lithium-Ion Batteries

Abstract

The construction of advanced nanostructures as well as the hybridization of different active materials are highly desirable for achieving lithium-ion batteries (LIBs) anode with superior electrochemical performance. In this work, flower-like Ni/NiO nanoflowers was prepared through a facile solvothermal route. Firstly, α-Ni(OH)2 was synthesized by heating Ni(NO3)2·6H2O precursor in methanol/water in the presence of PVP. After that, a two-step thermal annealing process was carried out. First, Ni-NiO was formed by annealing the α-Ni(OH)2 precursor under inert Ar environment. Subsequently, the Ni was annealed in air and partially oxidized to form NiO. The Ni/NiO ratio could be tuned by simply adjusting the annealing time in air. Alternatively, raw NiO could be obtained by directly annealing in air without the step annealing in Ar. It is found that amount of metallic Ni phase determined the lithium storage performance. When applied as the anode for LIBs, Ni/NiO nanoflowers exhibited an enhanced capacity of 994.6 mAh g-1 at 0.1 A g-1 after 70 cycles than the raw NiO (194.3 mAh g-1). As the integrated amount of Ni increased, the discharge capacity decreased to 828.4 mAh g-1. Thus, benefitting from the advantages of the intrinsic nanoarchitecture and the electrochemical catalysis of metallic nickel, NiO with appropriate Ni content is demonstrated to be well-suited for LIB anode with high capacity, remarkable rate capability and superior cycling stability. This work brings a novel direction to design metal/metal oxide hybrid nanostructured anode materials with excellent lithium storage performance.