Sodium Tetrakis(hexafluoroisopropyloxy)aluminates: Synthesis and Electrochemical Characterisation of a Room‐Temperature Solvated Ionic Liquid

Abstract

AbstractWeakly coordinating anions (WCAs) are used throughout chemistry to minimise cation‐anion interactions in the solid and solution states. The ability to suppress ion‐pairing has important bearings ‐ or impacts on the properties of materials, on single‐site catalysis and on ionic conductivity. Fluorinated alkoxy aluminates (containing [Al(ORF)4]− anions) are an attractive class of WCA owing to their high thermodynamic stability, stemming from strong aluminium‐oxygen bonds, and the ability to tailor their steric and electronic properties by changing the organic substituents (R). This work explores the structural and electrochemical properties of sodium tetrakis(hexafluoroisopropyloxy)aluminate, Na[Al(hfip)4] ⋅ xDME (hfip=hexafluoroisopropyloxy, OiPrF, DME=1,2‐dimethoxyethane, x=3 or 1). When solvated with one DME molecule, Na[Al(hfip)4] ⋅ DME is a room‐temperature solvated ionic liquid, with an activation energy of conduction of 0.4 eV. Both Na[Al(hfip)4] ⋅ 3DME and Na[Al(hfip)4] ⋅ DME have been studied as electrolyte salts for sodium‐ion batteries, where sodium‐ion cycling proceeds but with low capacity retention.