Accelerating S?Li₂S Reactions in Li-S Batteries through Activation of S/Li₂S with a Bifunctional Semiquinone Catalyst

The reaction rate bottleneck during interconversion between insulating S-8 (S) and Li2S fundamentally leads to incomplete conversion and restricted lifespan of Li-S battery, especially under high S loading and lean electrolyte conditions. Herein, we demonstrate a new catalytic chemistry: soluble semiquinone, 2-tertbutyl-semianthraquinone lithium (Li(+)TBAQ & sdot;(-)), as both e(-)/Li+ donor and acceptor for simultaneous S reduction and Li2S oxidation. The efficient activation of S and Li2S by Li(+)TBAQ & sdot;(-) in the initial discharging/charging state maximizes the amount of soluble lithium polysulfide, thereby substantially improve the rate of solid-liquid-solid reaction by promoting long-range electron transfer. With in situ Raman spectra and theoretical calculations, we reveal that the activation of S/Li2S is the rate-limiting step for effective S utilization under high S loading and low E/S ratio. Beyond that, the S activation ratio is firstly proposed as an accurate indicator to quantitatively evaluate the reaction rate. As a result, the Li-S batteries with Li(+)TBAQ & sdot;(-) deliver superior cycling performance and over 5 times higher S utilization ratio at high S loading of 7.0 mg cm(-2) and a current rate of 1 C compared to those without Li(+)TBAQ & sdot;(-). We hope this study contributes to the fundamental understanding of S redox chemical and inspires the design of efficient catalysis for advanced Li-S batteries.