Lithium Polysulfidophosphates: A Family of Lithium-Conducting Sulfur-Rich Compounds for Lithium-Sulfur Batteries

摘要

The conflict of the ever-increasing demand of energy consumption and the public concern over environmental issues demands a sustainable energy future that requires innovations on harvesting and delivering clean energies. Batteries have been brought into the spotlight as the pivotal technology for the electricity-based energy infrastructure that incorporates intermittent renewable energies. Although lithium ion (Li-ion) batteries have succeeded in powering personal electronics and small electric tools, they face the challenges of safety, cost, and energy density for the needs of independent electrified transportation and large-scale energy storage. As compared to the current Li-ion batteries, Lithium-sulfur (Li-S) batteries are a promising candidate technology with advantages of abundant materials and inherently high energy. However, achieving longevity of cycling in Li-S batteries is formidable because of the electrical insulating nature of elemental sulfur and the poor ionic conductivity of sulfur and its discharge products. After nearly four decades of research, significant progress has been made to Li-S batteries: various carbon materials and conducting polymers impart electronic conductivity to the sulfur cathode, and organic liquid electrolytes with good solubility to lithium polysulfides overcome the poor ionic conductivities of the sulfur cathode. Using a liquid electrolyte that dissolves lithium polysulfides is a necessity in cycling conventional Li-S batteries: sulfur is actually cycling as a solution, also known as the catholyte. The dissolved polysulfides move sulfur inside the electrochemical cells, which leads to parasitic side reactions that have been well-documented as the polysulfide shuttle (PS).