Experimental and ab initio based DFT calculation of NaFe0.5Co0.5O2 as an excellent cathode material for futuristic sodium ion batteries

Abstract

Owing to the low molecular weight of sodium containing layered metal oxides, they are unearthed as the high specific capacity cathode materials among other types for sodium ion batteries (SIBs). Among them, NaCoO2 (NCO) and NaFeO2 (NFO) are the two most studied cathodes for SIBs. NCO, as a positive electrode, shows high power density and theoretical capacity. Similarly, NFO is composed of earth abundant elements and hence cheaper comparatively with NCO, shows high redox potential, and has high structural stability. However, NCO is toxic due to the presence of cobalt, and is high moisture sensitive and shows multiphase transition. Similarly, NFO shows critical irreversibility and non-equilibrium phase transition at higher voltage. Inspired by the synergetic effect of Fe and Co, for the first time, a combined computational and experimental work is carried out on NaFe0.5Co0.5O2 (NFCO) to understand its potentiality as the cathode material for SIBs. The structural and electronic properties of NFCO are studied along with its end products NCO and NFO with the help of first principles-based density functional theory (DFT) calculation using B3LYP hybrid density functional. NFCO shows better electronic properties in terms of reduced band gap and enhanced electronic density of states (DOSs) compared to the end products. Experimentally, NFCO and its end products are synthesized via solgel method and various physicochemical characterizations such as Thermogravimetric Analysis-Derivative Thermogravimetric (TGA-DTG), Powder X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray Analysis (EDAX), and Raman spectroscopy are performed. Furthermore, the electrochemical performances for NFCO are carried out via Cyclic Voltammetry (CV), Galvanostatic Charge Discharge (GCD), Electrochemical Impedance Spectroscopy (EIS), and cycling stability analysis. NFCO delivers the specific capacities of 272.58 mAh/g and 225.63 mAh.g−1 at 1 A/g and 2 A/g current densities, respectively through the GCD analysis. NFCO cathode material exhibits remarkable cycling stability even after 4000 cycles with a good initial specific capacity retention. A maximum energy density of 37.86 Wh/kg at 1 A/g is observed for NFCO. The experimental and the DFT level of combined study reveals that NFCO could be a better choice as an excellent cathode material for the futuristic SIBs application. © 2023 Elsevier Ltd