Modulation Effects of Selected Additives on the Key Physicochemical Properties of AlCl3-EMImCl Ionic Liquid Electrolyte

The density, viscosity, electrical conductivity, and electrochemical window of aluminum chloride-1-ethyl-3-methylimidazole chloride (AlCl3-EMImCl) ionic liquid were systematically determined across a broad temperature range. The ionic liquid was functionalized with four inorganic additives (LiCl, LiBr, NaCl, NaBr) and three organic additives (ethylene carbonate (EC), tetrahydrofuran (THF), 1,2-dichloroethane (DCE)). The results demonstrate that inorganic additives increase the density of AlCl3-EMImCl, while organic additives result in a density reduction. Among all additives, DCE and THF show the most remarkable viscosity-reducing effects. Influence of additives on electrical conductivity follows the order: DCE > THF > LiCl, LiBr > NaCl, NaBr > blank > EC. Except for LiBr and NaBr, all other investigated additives do not narrow the electrochemical window of AlCl3-EMImCl. Soft-pack battery tests further validate that THF significantly enhances coulombic efficiency without obvious capacity decay. This work provides comprehensive experimental data and useful selection references for additives, supporting the potential application of AlCl3-EMImCl electrolytes in aluminum-ion batteries.