Metal iodides (LiI, MgI2, AlI3, TiI4, and SnI4) potentiality as electrolyte additives for Li-S batteries

Abstract

Lithium−sulfur (Li−S) batteries are being evaluated as low-cost and high-capacity next-generation secondary batteries to improve the mileage in electric vehicles. Accordingly, cathodes and electrolytes for Li−S batteries have been under active development in recent years. However, for the commercial use of Li−S batteries, it is first necessary to address the low electrical conductivity of sulfur particles as well as the low capacity retention caused by lithium polysulfide. We therefore investigated the effects of various metal iodides as additives in the electrolyte used in Li−S batteries. Metal iodides (i.e., LiI, MgI2, AlI3, TiI4, and SnI4) added to ether-based electrolytes impacted the charge–discharge performance as well as physical properties such as Li ion conductivity and viscosity. The extent of their impact depended on their concentration. Electrolytes that included LiI or MgI2 additives in particular formed a stable solid electrolyte interphase (SEI) layer on the Li metal and suppressed the polysulfide shuttle reaction. This is because the viscosity of the electrolyte is appropriately increased by polymerization, and Mg ions along with Li ions are deposited on the Li metal surface to form a stable SEI. Consequently, our approach demonstrates a strategy for developing new electrolytes for Li−S batteries that takes advantage of the chemical reactivity of the additives used in the electrolyte.