Electrorefining of Sodium in Sodium Bis(trifluoromethane)sulfonylimide and Tetrabutylammonium Bis(trifluoromethane)sulfonylimide Mixture Ionic Liquids for Metallic Sodium Recycling

摘要

To develop an electrorefining process for sodium to enable recycling of used sodium-sulfur batteries, a non-aqueous electrolyte with low melting point was investigated. A mixed ionic liquid of NaTFSI (sodium bis(trifluoromethane) sulfonylimide) - TBATFSI (tetrabutylammonium bis(trifluoromethane) sulfonylimide) was selected for the electrolyte. From AC impedance measurements, a maximum ionic conductivity of 16 mS cm(-1) was established of 20 mol% NaTFSI-TBATFSI concentration at 433 K. Electrorefining for 20 hours was carried out with a stable voltage under constant current electrolysis. Liquid pure sodium was electrodeposited by the constant current electrolysis. The calcium content in the sodium cathode was decreased from 250 to 52 ppm by the electrorefining. (C) 2014 The Electrochemical Society. All rights reserved.