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

Abstract

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.

Current status and future perspectives of lithium metal batteries

“…Effective HF scavengers contain simple electron-donating sites and form a complex with HF [56]. Lithium hexamethyldisilylimide scavenges HF and produces NH 3 , LiF and trimethylsilyl fluoride [57]. Scavenger additives overall improve the stability of LiPF 6 containing electrolytes and prolong cycle life.…”

PEDOT:PSS Dual-Function Film Initiated 1,3-Dioxolane Polymerization in Li/S Cells

“…It was revealed that the ring-opening polymerization of DOL usually occurred with cation involvement, mostly proton, and the typical mechanism is shown in Figure a. The proton-induced polymerization was verified by DOL being solidified by HF, either being added directly or indirectly generated by a fluoride-containing salt such as LiPF 6 . In addition, many other Lewis acids were found to catalyze DOL polymerization .…”

“…The protoninduced polymerization was verified by DOL being solidified by HF, either being added directly or indirectly generated by a fluoride-containing salt such as LiPF 6 . 31 In addition, many other Lewis acids were found to catalyze DOL polymerization. 32 Accordingly, here, PSS can also serve as the special "initiator reservoir" because of its acidic nature (Figure 1b).…”

“…The inherently different nature of acyclic and cyclic ethers could explain the phenomenon. DOL has a distinct cyclic structure containing acetal groups in which the centered carbon is linked to two adjacent oxygen atoms (RO− CH 2 −OR), while DME, though also being the diether, its linear structure led to disparate chemical reactivity, 31 more specifically, much less vulnerable to proton, and it could remain stable under acidic conditions. Thus, in order to get the desired effect, a single DOL solvent would be preferred.…”

Electrolyte Additives for Lithium Metal Anodes and Rechargeable Lithium Metal Batteries: Progress and Perspectives

“…Kim et al [141] investigated anovel approach of using LiPF 6 as al ithium salt for Li-S batteries.T he main obstacle was found to be the undesired acid-catalyzed, cascade-type polymerization reaction of DOL in the electrolyte.T he acid catalyst, hydrogen fluoride (HF), is generated in the reaction between the LiPF 6 salt and trace amounts of water. Three different HF scavengers,n amely,t rimethylamine (TEA), diethylaminotrimethylsilane (NTMSDE), and lithium hexamethyldisilylimide (LiHMDS), were thus investigated.…”