All-Solid-State Lithium-Sulfur Batteries Enhanced by Redox Mediators

Xin Gao; Xueli Zheng; Yuchi Tsao; Pu Zhang; Xin Xiao; Yusheng Ye; Jun Li; Yufei Yang; Rong Xu; Zhenan Bao; Yi Cui

doi:10.1021/jacs.1c07754

All-Solid-State Lithium-Sulfur Batteries Enhanced by Redox Mediators

J Am Chem Soc. 2021 Nov 3;143(43):18188-18195. doi: 10.1021/jacs.1c07754. Epub 2021 Oct 22.

Authors

Xin Gao¹, Xueli Zheng¹, Yuchi Tsao², Pu Zhang¹, Xin Xiao¹, Yusheng Ye¹, Jun Li^{1

2}, Yufei Yang¹, Rong Xu¹, Zhenan Bao³, Yi Cui^{1

4}

Affiliations

¹ Department of Materials Science and Engineering, Stanford University, Stanford, California 94305, United States.
² Department of Chemistry, Stanford University, Stanford, California 94305, United States.
³ Department of Chemical Engineering, Stanford University, Stanford, California 94305, United States.
⁴ Stanford Institute for Materials and Energy Sciences, SLAC National Accelerator Laboratory, 2575 Sand Hill Road, Menlo Park, California 94025, United States.

PMID: 34677957
DOI: 10.1021/jacs.1c07754

Abstract

Redox mediators (RMs) play a vital role in some liquid electrolyte-based electrochemical energy storage systems. However, the concept of redox mediator in solid-state batteries remains unexplored. Here, we selected a group of RM candidates and investigated their behaviors and roles in all-solid-state lithium-sulfur batteries (ASSLSBs). The soluble-type quinone-based RM (AQT) shows the most favorable redox potential and the best redox reversibility that functions well for lithium sulfide (Li₂S) oxidation in solid polymer electrolytes. Accordingly, Li₂S cathodes with AQT RMs present a significantly reduced energy barrier (average oxidation potential of 2.4 V) during initial charging at 0.1 C at 60 °C and the following discharge capacity of 1133 mAh g_s^-1. Using operando sulfur K-edge X-ray absorption spectroscopy, we directly tracked the sulfur speciation in ASSLSBs and proved that the solid-polysulfide-solid reaction of Li₂S cathodes with RMs facilitated Li₂S oxidation. In contrast, for bare Li₂S cathodes, the solid-solid Li₂S-sulfur direct conversion in the first charge cycle results in a high energy barrier for activation (charge to ∼4 V) and low sulfur utilization. The Li₂S@AQT cell demonstrates superior cycling stability (average Coulombic efficiency 98.9% for 150 cycles) and rate capability owing to the effective AQT-enhanced Li-S reaction kinetics. This work reveals the evolution of sulfur species in ASSLSBs and realizes the fast Li-S reaction kinetics by designing an effective sulfur speciation pathway.