Evolution of Water State in the “Ionic Liquid EAN/Al(NO₃)₃/H₂O” System Depending on Temperature and Aluminum Salt Concentration

Although lithium salts are the most successful materials for electrochemical devices so far, there is growing interest in electrolytes containing divalent and trivalent salts, which are characterized by a much higher energy density than lithium systems. For this purpose, the physical and chemical properties of solutions of aluminum nitrate in ethylammonium nitrate (EAN) were studied in a number of works. However, it was demonstrated by the ¹H NMR method that solutions contain water (from aluminum crystallohydrates) in the first solvated shell of the Al³⁺ cation even after usual drying procedures, and this solvated water cannot be directly detected by the standard Karl Fischer analysis. The goal of this work is to check the possibility/impossibility of removing water from the "Ionic Liquid EAN/Al(NO₃)₃/H₂O" system and to investigate the evolution of water state in the system depending on temperature and aluminum salt concentration. To solve the problem, the NMR spectroscopy of ¹H, ²⁷Al, and ¹⁴N nuclei was used. To interpret the NMR spectra, quantum-chemical calculations of electron shielding constants for the ¹H and ²⁷Al nuclei in mixed cation-anion complexes were involved.