Effect of acid scavengers on electrochemical performance of lithium-sulfur batteries: Functional additives for utilization of LiPF6

We investigated a novel approach for utilizing LiPF6 as the lithium salt for Li-S batteries and verifying its chemical reactivity with the main solvent. It is found that the main obstacle for the adoption of LiPF6 is the undesired acid-catalyzed, cascade-type polymerization reaction between cyclic ether components in the solvent and LiPF6. Therefore, several kinds of acid scavengers are proposed to enhance the chemical stability between the main solvent and LiPF6. Simple storage tests indicate that polymerization occurred as acid residue is removed from the electrolyte. Consequently, the cell with a modified electrolyte shows excellent discharge capacity and moderate retention based on its improved chemical stability. These results indicate that assuring the chemical stability is the most important factor to utilizing LiPF6 as the main lithium salt for a Li-S cell. Additionally, it is believed that an understanding of the nature of chemical reactivity will be beneficial to constructing more efficient electrolyte systems owing to enhanced electrochemical performance of many kinds of energy storage systems including Li-S, Li-air, and metal-air batteries.