(Digital Presentation) Understanding the Influence of Fe Doping Level on Na-Ion Diffusivity for P2-Na_2/3Mn_1-XFe_xO₂ (x= 0, 1/3, 1/2) sodium-Ion Battery Cathode Material Using Molecular Dynamics Simulation

Abstract

Global progression towards e-mobility to reduce the carbon footprint has led to the demand for smart grid energy storage systems. Amongst the available electrical energy storage technologies, rechargeable batteries serve as a pragmatic option to cater to the intermittent character of renewable energy supplies owing to their high energy efficiency and flexible power characteristics. In contrast to the existing lithium-ion batteries (LIBs), Na-ion batteries appear as a sustainable substitute due to their dependence on widely distributed, and abundant sodium reserves. However, the commercialization of Na-ion batteries has been hampered primarily by the inefficient performance of electrode materials particularly cathode. Among the prevailing cathode materials, the class of layered transition metal oxide with O3 and P2 structural configuration imparts decent specific capacity and has been studied extensively over the past few years. Though the presence of comparatively larger Na ions induces better initial capacity but suffer the drawback of undergoing complex phase transformation during charge-discharge cycling. Moreover, P2-phase exhibits lower diffusion energy barrier due to the direct passage of sodium ions from one prismatic site to another. Therefore, materials with the aforementioned P2 orientation have been synthesized deploying earth-abundant elements like Mn, and Fe for sodium-ion battery applications. To comprehend the diffusional behavior of Na-ions, we have carried out molecular dynamics simulation of P2-Na2/3Mn1-xFexO2 (x=0, 1/3, 1/2) material. The preliminary computational calculations reveal enhanced Na-ion self-diffusivity with increased Fe dopant onto P2-Na2/3MnO2 material, while the diffusivity showcased a decreasing trend with further increase in Fe substitution that might be ascribed to the phase stabilization aspect of Mn element and charge compensation attribute of Fe3+/Fe4+ and Mn3+/Mn4+ redox couples.