Sodium Ion‐Conducting Electrolytes Based on Chloroaluminate Ionic Liquids and δ‐NaCl

Abstract

AbstractSodium‐containing ionic liquids are very promising candidates as ion‐conducting materials in alternative to electrolytes based on lithium chemistry. Here we investigate a series of seven ionic liquids with formula (EMImCl/(AlCl3)1.5)/(δ‐NaCl)x (0≤x≤0.74). The salt is comprised of a disordered form of NaCl prepared by metalorganic synthesis, which assures faster dissolution in high concentration. The vibrational investigation carried out by FT‐IR spectroscopy in the medium IR region shed light on salt‐IL interactions. The ionic conductivity was investigated by Broadband Electric Spectroscopy. The direct current conductivity (σdc) profiles versus the reciprocal temperature exhibited a Vogel‐Tamman‐Fulcher behavior indicating the assistance of micro‐Brownian motions to ionic migration. The value of σdc at 25 °C for x=0.74 was found to be 1.2×10−2 S cm−1. Reversible deposition of Na and Al‐containing species take place with high Coulombic efficiency (up to 97 %) and a high Na+ cation transport number (up to 0.95). The understanding of ionic speciation was investigated in comparison with aqueous acid‐base systems exploring the benefits and limitations of such analogy. The role of a Grotthuss‐type mechanism facilitating the exchange of chlorides between acidic catenated chloroaluminate species in anionic domains of the ILs is considered.