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

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AbstractThe reaction rate bottleneck during interconversion between insulating S8 (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⋅−), as both e‐/Li+ donor and acceptor for simultaneous S reduction and Li2S oxidation. The efficient activation of S and Li2S by Li+TBAQ⋅− 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⋅− 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⋅−. 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.