Complexation of F– by Li+ and Mg2+ Ions as Inorganic Anion Acceptors in Lactone-Based Li+/F– and Mg2+/F– Hybrid Electrolytes for Fluoride Shuttle Batteries. Issue 11 (1st November 2022)

• Record Type: Journal Article
• Authors: Kawasaki, Mitsuo; Morigaki, Ken-ichi; Kano, Gentaro; Takekawa, Reiji; Kawamura, Junichi; Yokoyama, Yuko; Kano, Kenji; Abe, Takeshi; Ogumi, Zempachi
• Is Part Of: Journal of the Electrochemical Society. Volume 169:Issue 11(2022)
• Publication Date: 2022-11-01
• Subjects: Electrochemistry -- Periodicals; 541.3705
• DOI: 10.1149/1945-7111/ac9a05
• Languages: English
• ISSNs: 0013-4651

Abstract

Abstract : The development of high-quality fluoride-ion transporting electrolytes is a crucial demand for fluoride shuttle batteries (FSBs). However, the uncontrolled chemical and electrochemical activities of fluoride ions narrow the available potential window, hindering the development of high-voltage FSB cells. We present a method for upgrading recently developed lactone-based liquid fluoride electrolytes by complexation of F – with Li + and Mg 2+ ions. In the resultant Li + /F – and Mg 2+ /F – hybrid electrolytes, Li2 F + and MgF + were the most probable soluble complexes, and the effective fluoride concentrations could reach ∼0.15 M along with excess Li + (Mg 2+ ) ions. Unique interactions between F – and Li + (Mg 2+ ) were observed using 19 F nuclear magnetic resonance spectroscopy. Li + (Mg 2+ ) ions thus served as inorganic anion acceptors with ultimate redox stabilities to expand the negative potential window of the electrolytes to near −3 V vs SHE. The proposed complex formation was also supported by a conductometric titration method. We demonstrated the superior and versatile electrochemical performances of the Li + /F – hybrid electrolyte, which enabled reversible charge/discharge reactions of various metal electrodes and composite electrodes in a wide range of redox series. Further, the Li + /F – hybrid electrolyte opened valid new reaction paths for aluminum, making it a promising negative electrode in high-voltage FSB cells.