Low-Cost Fluoride Source for Organic Liquid Electrolyte-Based Fluoride Shuttle Battery
Asuman Çelik Küçük, Toshiro Yamanaka, Yuko Yokoyama, Takeshi Abe
Abstract
The effects of using low-cost inorganic fluoride salts (i.e., KF or NaF) as fluoride sources in fluoride shuttle batteries (FSBs) on the electrochemical compatibility of BiF 3 electrodes are investigated herein. The preparation of electrolytes containing saturated KF or NaF and 0.5 M 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (DiOB-Py) in G4 is described. For Py/NaF/G4, the discharge and charge reactions of BiF 3 were hindered because of the low solubility of NaF as well as the low ionic conductivity of the electrolyte. However, inductively coupled plasma mass spectrometry (ICP-MS) analysis revealed that the solubility of KF in Py/KF/G4 was moderate and the ionic conductivity of Py/KF/G4 was promising. Higher oxidation and reduction peaks observed in the cyclic voltammograms of Py/KF/G4 than those of Py/G4 and Py/NaF/G4 are attributed to the enhanced electrochemical activity of the former. Consequently, the BiF 3 /C nanocomposite electrode exhibits good cycling capability in Py/KF/G4, with initial discharge/charge capacities of 316/218 mAh g −1 , respectively. Moreover, the ICP-MS and Raman spectroscopy analyses revealed that defluorination reactions of BiF 3 occur via a direct desorption mechanism. Py/KF/G4 is the first effective electrolyte based on a low-cost inorganic salt. FSBs exhibit improved performance in Py/KF/G4 compared with CsF salt systems, which warrants further investigation.