Stability Analysis of Manganese-Oxides As Cathodes for Sodium Ion Batteries

Batteries are among the most widely used energy storage devices worldwide. With demand rising, as renewable energy storage and electric vehicles gain popularity in the face of climate change, exploring battery chemistries beyond lithium has become increasingly important. Sodium-ion batteries are one of the most promising alternatives, offering the advantage of lower costs, reliable safety, and high earth-abundance. Within sodium ion batteries, manganese-oxides are a popular choice of cathode material for similar reasons. The present work seeks to analyze the viability and performance of manganese-oxide frame-works for sodium-ion battery cathodes. Density Functional Theory and Coulombic energy calculations are used to evaluate the stability of pyrolusite (MnO2, space group P42/mnm), ramsdellite (MnO2, Pnma), hollandite (Mn8O16, I4/m) , romanechite (Mn5O10, C2/m), and birnessite (Mn4O8, C2/m) with Nax contents ranging from empty to full (x = 0, 0.25, 0.33, 0.5, 0.66, 0.75, 1) in each structure. Hollandite is shown to be the most promising structure due to its high stability and the nature of its energy landscape which facilitates diffusion and withstands Jahn-Teller effects better than its manganese oxide counterparts. Understanding the role of sodium content in structural stability and performance within each crystal structure aims to push forward our understanding of sodium ion batteries and their potential for next generation energy storage