Electrodeposition of Al, Al-Li Alloy, and Li from an Al-Containing Solvate Ionic Liquid under Ambient Conditions

Abstract

Herein, inspired by previous reports on the electrochemical reduction of Al in diverse electrolyte systems, we describe a novel Al-containing solvate ionic liquid (2:1 (mol/mol) mixture of ethylene carbonate (EC) and AlCl 3 ) that allows low-temperature electrochemical deposition of Al and features the advantages of low cost, ease of preparation, and high electrochemical stability. Electrodeposition of Al-Li alloy and Li can also be realized in this system. Additionally, the above ionic liquid exhibited a saturated vapor pressure of 0.0012 kPa and a conductivity of 1.32 mS/cm at 298 K, which was acceptable for practical applications. To elucidate the electrochemical deposition mechanism, the ionic components of the 2:1 EC/AlCl 3 system were characterized by a range of instrumental analysis techniques and theoretical calculations, and Lewis-acidic cations were identified as the electroactive species for Al electrodeposition. Notably, an Al-Li alloy could be obtained by co-deposition in the new solvate ionic liquid, and Li metal could also be electrodeposited on a high-purity Al plate in the form of Al 4 Li 9 and Li 3 Al 2 under ambient conditions using LiCl as a Li source. Al-containing solvate ionic liquids, which to an extent evolved from organic-salts, are of increasing interest. They are expected to gain more attention in the field of electrochemical metallurgy of active metals, due to their higher tunability and lower price.

Direct Electrochemical Deposition of Lithium from Lithium Oxide in a Highly Stable Aluminium‐Containing Solvate Ionic Liquid

“…The synthesis method and 27 Al NMR analysis of the ILlike system were described in our previous publication. [15] It should be noted that first introducing Li 2 O to EC and then adding AlCl 3 to the mixture enhanced dissolution. The geometries of EC, Li 2 O, and AlCl 2 + and their binary mixtures were optimized using DFT/BLYP/6-31G* calculations and energetic values were generated at the B3LYP/6-31G* level of theory.…”

“…However, the abovementioned metal salts can also be dissolved in chloroaluminate IL-like systems, even though there are no [Al 2 Cl 7 ] À Lewis acid anions, [15] as the Lewis acidity is imparted by the Al-containing cations. It is now accepted that the reaction between AlCl 3 and ligands forms both Al containing anionic and cationic species according to Equation (2), [11,12,13,17] where this reaction is exothermic.…”

“…However, such cations have never been reported in the literature, and there is no direct spectroscopic evidence for its existence. [15,19] However, Lewis acidic complex cationic species in the form of [AlCl 2 (base) n ] + have been increasingly observed by multinuclear nuclear magnetic resonance (NMR) spectroscopy. [10,15,20] Accordingly, chloride metal salts can also be easily dissolved in the Al-containing solvate IL in the presence of [AlCl 2 (base) n ] + [Equation (3)].…”

“…[10] Therefore, the discovery of new and stable ligands to extend the family of IL-like systems for practical applications in various fields is of fundamental significance.Recently, we described an electrochemically stabilized Alcontaining solvate IL (2 : 1 (mol/mol) mixture of ethylene carbonate (EC):AlCl 3 ) with Lewis-acidic cations; this allowed the electrodeposition of Al, AlÀLi alloys, and Li under ambient conditions. Advantages of this system include low cost, facile preparation, and high tuneability, [15] while excellent ability to dissolve metal chlorides was observed due to the strong Lewisacidic cations. In order to explore the feasibility of oxide dissolution in this liquid, a series of oxides (including Li 2 O, MgO, Al 2 O 3 , Nd 2 O 3 , and TiO 2 ) were dissolved in this system for metal electrowinning.…”

Aluminum Electrodeposition from Chloride-Rich and Chloride-Free Organic Electrolytes

“…The development of an organic electrolyte, however, is a challenging task that requires a fundamental understanding of the solute/solvent ion-dipole and coulombic interactions. 32 Tremendous efforts have been dedicated to electrodeposit Al from a plethora of organic systems including AlCl 3 and lithium hydride(LiH) in diethyl ether, 33 AlCl 3 and lithium aluminum hydride (LiAlH 4 ) in tetrahydrofuran (THF) and benzene mixture, 34 AlCl 3 and LiAlH 4 in THF and toluene, 35 AlCl 3 and LiAlH 4 in THF, [36][37][38][39] aluminum tribromide(AlBr 3 ) in aromatic hydrocarbons, 40,41 AlBr 3 in N,N-dimethylaniline, 42 AlBr 3 and potassium bromide (KBr) in ethylbenzene, 43 AlCl 3 in sulfones, [44][45][46][47][48][49] AlCl 3 in glycol ethers (glymes), [50][51][52][53] AlCl 3 in ethylene carbonate, 54 and AlCl 3 in gamma-butyrolactone (GBL). 55 Unfortunately, these electrolytes are inherently corrosive and the prospects of practically implementing rechargeable Al batteries as electrochemical energy storage devices is contingent upon active chloride-free systems.…”