Understanding the Redox Obstacles in High Sulfur-Loading Li-S Batteries and Design of an Advanced Gel Cathode.

Lithium-sulfur batteries with a high energy density are being considered a promising candidate for next-generation energy storage. However, realization of Li-S batteries is plagued by poor sulfur utilization due to the shuttle of intermediate lithiation products between electrodes and its dynamic redistribution. To optimize the sulfur utilization, an understanding of its redox behavior is essential. Herein, we report a gel cathode consisting of a polysulfide-impregnated O- and N-doped porous carbon and an independent, continuous, and highly conducting 3-dimensional graphite film as the charge-transfer network. This design decouples the function of electron conduction and polysulfide absorption, which is beneficial for understanding the sulfur redox behavior and identifying the dominant factors leading to cell failure when the cells have high sulfur content and insufficient electrolyte. This design also opens up new prospects of tuning the properties of Li-S batteries via separately designing the material functions of electron conduction and polysulfide absorption.