# Magnetic-field-guided catalytic effect mitigates Li2S passivation of lithium–sulfur batteries

## TL;DR

Applying a magnetic field to a catalyst in lithium-sulfur batteries helps reduce performance issues by improving sulfur recycling and battery stability.

## Contribution

Introducing magnetic-field-guided catalysis to simultaneously address polysulfide shuttle and Li2S passivation in Li–S batteries.

## Key findings

- A 400-mT magnetic field enhances α-Fe2O3's catalytic activity for polysulfide conversion and Li2S deposition/dissociation.
- Magnetic alignment and electron spin polarization improve the interaction between α-Fe2O3 and sulfur species.
- The modified cathode shows excellent cycling stability and rate capability in Li–S batteries.

## Abstract

Polysulfides shuttle and Li2S passivation are considered key problems of lithium–sulfur (Li–S) batteries, seriously hindering sulfur recycling for practical applications. However, the prevailing strategies for introducing electrocatalysts focus mainly on the polysulfides-shuttle effect, whereas Li2S passivation involving solid conversions with high energy barriers has been rarely studied and remains challenging. Herein, we propose that applying a magnetic field (MF) to weak ferromagnetism α-Fe2O3 shows an enhanced effect, not only suppressing the polysulfides shuttle, but also alleviating Li2S passivation by synchronously catalysing polysulfides conversion and Li2S deposition/dissociation. Experimental and theoretical studies reveal that the MF can promote the consistent alignment of magnetic-domain orientations in α-Fe2O3 and enhance the electron spin polarization of the Fe 3d orbital, which shifts the center of the Fe d-band towards the Fermi level and increases the hybridization degree between Fe 3d and S 3p orbitals in α-Fe2O3–Li2S6 or α-Fe2O3–Li2S, thus enhancing the adsorption and catalysis of polysulfides and solid products. As a result, after using a 400-mT MF, the α-Fe2O3/S cathode shows outstanding cycling stability and excellent rate capability. The research demonstrates that MF-guided electrocatalysis represents an effective solution to the challenging problems of Li–S batteries.

Magnetic field-guided catalytic effect over catalyst promotes not only polysulfide conversion but also Li2S deposition/dissociation via forming electroactive loose Li2S, synchronously suppressing polysulfide shuttle and Li2S passivation for high-performance Li-S batteries.