Spinel NiCo2O4 As a Promising Electrode Material for Li-Ion and Li-O2 Batteries

Secondary Li-ion batteries have played an important role as an energy storage device for portable electronics and electric/hybrid electric vehicles (EV/HEV). However, the energy density of conventional Li-ion battery is not sufficient, and thus a Li-O₂ battery can be a potential alternative to Li-ion batteries due to its much higher energy density.

In addition, transition metal oxides with nanostructural characteristics have shown good performance due to their advantage of high surface to volume ratio and short length for Li-ion diffusion in comparison with their bulk counterparts.  Previous studies showed that the spinel NiCo₂O₄ is an excellent candidate as an electrode material for Li-ion and Li-air batteries. NiCo₂O₄, a well-known cobalt-nickel spinel oxide, owns two solid-state redox couples (Co³⁺/ Co²⁺ and Ni³⁺/Ni²⁺) in the structure, which enables to exhibit a remarkable elctrocatalytic activity. In the present study, we have investigated the electrochemical performance of spinel NiCo₂O₄, as an anode material for Li-ion battery and cathode material for Li-O₂ battery.  

In the present study, spinel NiCo₂O₄ has been synthesized by simple and inexpensive urea assisted co-precipitation method and subsequent annealing at 400 ^oC for 2h.The TG and DSC analysis was carried out to analyze the weight loss during heat treatment. The spinel structure of NiCo₂O₄ was confirmed by the X-ray diffraction (XRD) analysis. The FE-SEM analysis reveals the formation of spinel NiCo₂O₄ with urchin like structure, composed of several nanorods. The nanorods are highly porous consisting of interconnected nanoparticles confirmed by TEM analysis. The N₂ adsorption-desorption was carried out to investigate the surface area and porosity of spinel NiCo₂O₄. The electrochemical investigation of spinel NiCo₂O₄ as an anode material for Li-ion showed excellent cyclability (~1020 mAh.g^-1 at 0.2C upto 200 cycles) and superior rate capability. The use of spinel NiCo₂O₄ as cathode material in Li-O₂ cell, exhibit an excellent performance reasonable specific capacity, and lower overpotential. In conclusion, Spinel NiCo₂O₄ can be a potential candidate as an electrode material for Li-ion and Li-air batteries.