Facile Synthesis of Hollow Mesoporous NiCo 2 O 4 Nanostructures and Their Structural Evolution By Synchrotron X-Ray Diffraction As a Negative Electrode in Lithium-Ion Batteries

Mesoporous hollow nanostructures have been attracting remarkable attention because of their high surface area, robust structure and are indispensably have a great scope for basic studies. On the other side, binary metal oxides are considered to be as promising anode materials for lithium ion batteries, especially, NiCo 2 O 4 is of a great virtue to overcome the current existing hurdles with anode materials, such as reversible capacity, structural stability, and electronic conductivity. Also, the reduction of high-cost and toxic metal, Co content in the NiCo 2 O 4 in comparison with pure Co 3 O 4 makes it more significant for mainstream applications. Herein we report a facile chemical synthesis method followed by thermal annealing in the air to attain three-dimensional (3D) arrangement of mesoporous NiCo 2 O 4 hollow nanoparticles that are randomly organized into bundles of superstructures. This method can produce highly reproducible structures with gram quantities. Brunauer−Emmett−Teller (BET), Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the surface area of the synthesized materials is determined to be 134 m 2 g -1 (narrow pore size distribution of 3-4 nm) with a unique porous morphology including nanoparticles/ flakes of about 5 to 50 nm in size range appeared on the surface of each hollow particle exert significant influence on the electrochemical performance. It is evidently exhibited by NiCo 2 O 4 hollow superstructures electrode that the increase in lithium storage capacity and excellent cycling stability (1335 mA h g −1 at a current density of 100 mA g −1 after 30 cycles). Further, we have investigated the structural evolution of this new morphological electrode material by ex-situ X-ray diffraction using synchrotron X-ray beam during first and second consequent cycles tested at low scan rate (100 mA g −1 ). Moreover, this synthesis strategy can be extended to the preparation of other metal oxides for energy storage devices and for many other related applications.