Advances on Composite Cathodes for Lithium-Sulfur Batteries

Lithium-sulfur (Li-S) batteries are deemed as high-promising next-generation energy storage technique due to their ultrahigh theoretical energy density, where the sulfur cathodes with high specific capacity guarantee the energy density advantage and directly determine the battery performances. After decades of exploration, the most promising sulfur cathodes are sulfur/carbon composite (S/C) cathodes and sulfurized polyacrylonitrile (SPAN) cathodes. In this manuscript, recent advances on S/C and SPAN cathodes in Li-S batteries are comprehensively reviewed. The electrochemical reaction circumstances on S/C and SPAN cathodes are firstly introduced and compared to reveal the working mechanisms of the two types of Li-S batteries. The S/C cathodes mainly undergo solid-liquid-solid multi-phase conversion processes with typical double-plateau charge-discharge polarization curves. In comparison, the SPAN cathodes follow solid-solid conversion and exhibit single-plateau charge-discharge characteristics. Following that, key challenges and targeted optimizing strategies of the S/C and SPAN cathodes are respectively presented and discussed. For Li-S batteries with S/C cathodes, the main optimizing strategies are electrode structure modification, efficient electrocatalyst design, and redox comediation. For SPAN cathodes, the main optimizing strategies are electrode structure modification, morphology regulation by co-polymerization, heteroatom doping at molecular level, and extrinsic redox mediation. At last, current research status of Li-S batteries with S/C or SPAN cathodes are systematically analyzed through the comparison of several battery parameters, and perspectives on challenges and opportunities of S/C and SPAN cathodes in Li-S batteries are presented to guide future researches.