# Tailored Redox‐Active Catholytes Enabling High‐Rate and High‐Loading All‐Solid‐State Lithium‐Sulfur Batteries

## TL;DR

This paper introduces a new solid electrolyte design for lithium-sulfur batteries that improves performance by enabling faster reactions and higher sulfur usage.

## Contribution

The study introduces iodine-substituted solid electrolytes with redox activity, enabling high-rate and high-loading all-solid-state lithium-sulfur batteries.

## Key findings

- Cells achieved 86% sulfur utilization at C/2 rate and 45°C.
- High-rate capability of 1175 mAh/g at 5C and 590 mAh/g at 15C was demonstrated.
- Record areal capacities of 14 mAh/cm² were achieved with 10 mg/cm² sulfur loading.

## Abstract

All‐solid‐state lithium‐sulfur batteries (ASSLSBs) hold great promise for next‐generation electrochemical energy storage due to sulfur's high theoretical specific capacity and low cost. However, sluggish sulfur conversion kinetics and severe volume variations during cycling, as well as poor ionic percolation in composite cathodes, limit their practical viability. To overcome these challenges, we herein introduce solid electrolytes of nominal composition Li10.5−

x
Si1.5P1.5S12−

x
I
x
(with x = 0, 0.2, 0.4), possessing high ionic conductivities of ≥ 7 mS cm−1 at room temperature. We show that increasing iodine content alters the phase composition and triggers reversible redox activity in these materials. If implemented as catholytes, this enables very fast sulfur conversion kinetics, ultimately leading to ASSLSBs with exceptional performance. The cells achieve 86% sulfur utilization at a rate of C/2 and at 45°C and offer high‐rate capability by delivering 1175 mAh gsulfur
−1 at 5C and 590 mAh gsulfur
−1 at 15C. Furthermore, the synergistic effects of ionic percolation and redox‐activity enable record areal capacities up to 14 mAh cm−2 with a sulfur loading of 10 mg cm−2. Taken together, our findings provide new strategies for designing redox‐active catholytes for application in advanced ASSLSBs and further strengthen the redox‐mediating role of iodine therein.

This study explores iodine substitution in solid electrolytes to overcome sluggish redox kinetics and poor charge transport in all‐solid‐state Li‐S batteries. The resulting iodine‐rich, amorphous phase and superionic, nanocrystalline domains enable effective redox mediation and provide a robust ionic percolation network. This synergy enhances sulfur utilization and conversion kinetics, pointing to a promising path for high‐performance Li‐S batteries.