# The role of disorder in NaO$_2$ and its implications for Na-O$_2$ batteries

## TL;DR

This study uses DFT with Hubbard U correction to explore structural and magnetic disorder in NaO₂, revealing complex magnetic phases and their implications for Na-O₂ battery performance.

## Contribution

It introduces a 3-body Ising Model combined with Monte Carlo simulations to accurately describe disorder in NaO₂, advancing understanding of its properties in batteries.

## Key findings

- NaO₂ exhibits significant rotational and magnetic disorder.
- Ferromagnetic phases near room temperature form alternating orthogonal O₂ dimers.
- Bulk NaO₂ structures are insulating with some ferromagnetic structures showing a small electronic gap.

## Abstract

We present a DFT study utilizing the Hubbard U correction to probe structural and magnetic disorder in $\mathrm{NaO_{2}}$, primary discharge product of Na-O$_2$ batteries. We show that $\mathrm{NaO_{2}}$ exhibits a large degree of rotational and magnetic disorder; a 3-body Ising Model is necessary to capture the subtle interplay of this disorder. MC simulations demonstrate that energetically favorable, FM phases near room temperature consist of alternating bands of orthogonally-oriented $\mathrm{O_{2}}$ dimers. We find that bulk structures are insulating, with a subset of FM structures showing a moderate gap ($<2$ eV) in one spin channel.