Understanding the Electrolytes of Lithium-Sulfur Batteries

Abstract

Lithium-sulfur batteries have been identified as an ultimate successor to lithium-ion batteries due to their unique properties such as extremely high theoretical specific capacity (1672 mAh g(-1)), low cost, abundance of elemental sulfur on earth's crust and environmental friendliness. However, the insulating nature and volume expansion (approximately 76 %) of elemental sulfur, shuttling of polysulfides between the two electrodes and poor interfacial properties of lithium metal anode with non-aqueous liquid electrolytes still hinder the commercialization of this system. In order to mitigate the shuttling of polysulfides between two electrodes, several strategies have been adopted, including optimizing the compositions, lithium salt and additives of non-aqueous liquid electrolytes, and replacing the non-aqueous liquid electrolyte with ionic liquids (ILs), solid polymers, superionic conductors, and quasi-solid-state electrolytes. This review article comprehensively covers the architecture, working principles of lithium-sulfur batteries, the state-of-the-art electrolytes, their types, properties, advantages, and limitations. The importance of electrolyte additives in enhancing the safety issues of lithium-sulfur batteries is also emphasized. Here, we provide an overview of recent developments in different types of electrolytes for lithium-sulfur batteries, focusing on electrochemical properties, and more specifically discussing issues related to polysulfide shuttles.