Physicochemical Properties Of AlCl₃ Based Room Temperature Molten Salts

Based on the applications of AlCl3-based room temperature molten salts on material surface finishing,metal electrodeposition and aluminum-ion secondary battery,etc.,this work studied the physicochemical properties of AlCl3-1-ethyl-3-methylimidazole chloride and(EMIC)systems,AlCl3-acetamide(AA)systems and AlCl3-urea(UR)systems.The molar ratio of AlCl3/IL(IL=EMIC,AA,UR)was 1.3,and 5 mol%additives including LiCl,LiBr,NaCl,NaBr,EC(Ethylene carbonate),THF(tetrahydrofuran),DCE(1,2-dichloroethane),EMIC were added to these three systems,separately,to investigate their effects on physical properties.The density was measured by Archimedean method,and viscosity by the capillary method,and conductivity by the impedance method in a capillary cell with fixed cell constant.The electrochemical windows of the melts were studied by the cyclic voltammetry.The structures of the investigated salts were studied by Raman spectroscopy.The effects of temperature and additives on the physicochemical properties and structure of room temperature molten salt systems were discussed in this paper.For all investigated systems,there is a linear relationship between density and temperature;the relationship between conductivity and temperature follows the VTF equation and the Arrhenius equation;viscosity is inversely proportional to electrical conductivity.For all systems with the same additive at the same temperature,the density is in the order:AlCl3-UR-additives>AlCl3-AA-additives>AlCl3-EMIC-additives;viscosity is in the order:AlCl3-UR-additives ≈AlCl3-AA-additives>AlCl3-EMIC-additives.The electrotrical conductivity is in the order:AlCl3-EMIC-additives>AlCl3-UR-additives ≈ AlCl3-AAadditives.According to the results of cyclic voltammetry curves,additives do not substantially change the cathodic limits and anodic limits of the investigated systems,and the electrochemical window range is between 2.5-2.6V.Raman spectroscopy indicated that Al2Cl7and AlCl4-complex ions are the main complexes in the three systems.After adding the additives,the Al2Cl7-content in the system reduced,while the AlCl4-content relatively increased.Among all the inorganic additives,the melts with LiCl have the lowest density and viscosity and the highest conductivity.Among all the organic additives,the melts with DCE have the lowest density and viscosity and the highest conductivity.Addition of ionic liquid EMIC to AlCl3-acetamide system or AlCl3-urea system can significantly improve their properties.