Novel P2-Type Na0.66Fe0.5-2xMn0.5TixVxO2 Cathode for High-Capacity

Abstract

Necessity of energy storage and battery production is soaring up day by day due to the growth of portable electronic devices and surging evolution of electric vehicles (EVs), plug-in-hybrid electric vehicles (PHEVs) and renewables. Lithium-ion battery (LIB) technology has been the primary choice for such applications due to its high-energy-density, high-stability, and longer cycle life. Albeit with all merits of LIB, the prime concern has been the scarcity of lithium in earth’s crust and depletion of lithium reserve due to its wide usage in batteries, resulting in a higher production cost. This has prompted battery researchers to search for new alternatives to LIB for energy storage applications. Sodium, in this respect, can be a viable solution as it is the sixth most abundant element and shares the same group with lithium in the periodic table. Sodium has similar structural and electrochemical working mechanisms of lithium. The pivotal factors hindering the deployment of the laboratory-based sodium-ion battery (SIB) technologies into the commercial energy storage market are low energy density compared to that of LIB, lower stability, lower ion-transport mechanism, and lower operating voltage. Improvement of overall electrochemical performance of cathode materials can be a game-changer as it affects the energy density, lifespan, and tolerance of batteries. In this research, a cobalt-free novel P2-type transition metal cathode Na0.66Fe0.5-2xMn0.5TixVxO2 was synthesized by doping NaFeMnO2 with vanadium and titanium for SIB battery applications. The cathode was synthesized based on a sol-gel reaction where citric acid was used as a chelating agent. A set of physicochemical analysis, including Field-Effect Scanning Electron Microscopy (FESEM) and Energy Dispersive X-ray Spectroscopy (EDAX) analysis, as well as electrochemical analysis like Cyclic Voltammetry and Galvanometric Charge/ Discharge were performed to understand the correspondence between layered transition metal oxide chemistry, surface morphology and electrochemical competence of the new material. The crystal structures of the pristine material and cathodes containing different percentages of doped vanadium and titanium were examined and lattice parameters were refined through X-ray Diffraction (XRD) and Rietveld analysis. These exhaustive structural and morphological comparisons were performed between the pristine and modified NaFeMnO2 (NFM) cathode structures, which provided insights on the effects of vanadium and titanium doping on stabilizing surface structures, reducing Jahn-Teller distortion, enhancing stability and capacity retention and promoting Na+ carrier transport mechanism.