In Situ/Operando Spectroscopic Characterizations Guide the Compositional and Structural Design of Lithium-Sulfur Batteries

Lithium-sulfur batteries have gained incredible increasing attention due to their high theoretical energy density and comparable low cost. Although great advances are made in optimizing Li-S batteries via rational design of the composition and architecture, daunting challenges remain to restrain the shuttle-effect issue associated with the extremely complicated solid-liquid-solid reaction routes. In recent years, researchers have reached a consensus that the characterization of practical working mechanisms of Li-S batteries is an important prerequisite for optimizing their performance. Numerous in situ/operando spectroscopic techniques with light sources of 10(-10)-10(3) m wavelengths, such as X-rays, UV-vis, nuclear magnetic resonance (radio), infrared, etc., are introduced to supply real-time and console-displayed signals related to the reaction variations of Li-S batteries, thus helping to put forward further optimization strategies in the internal designs. This review systematically summarizes the state-of-the-art in the optimal design of Li-S batteries with the aid of in situ/operando spectroscopic characterizations, including the progress in cathodes, binders, interlayers, electrolytes, and Li metal anodes, aiming to show the powerful ability of in situ/operando spectroscopic techniques in revealing the working and degradation mechanism and scientifically guiding the further optimal design of Li-S batteries.