Interplay between coordination, dynamics, and conductivity mechanism in Mg/Al-catenated ionic liquid electrolytes

The development of batteries based on alternatives to lithium is essential to sustaining the increasing global energy demand. Earth abundant, energy dense metal anodes with mixed multivalent ions (e.g., Mg/Al) are promising next-generation systems. A critical challenge, however, is the development of advanced electrolytes that are compatible with them. To achieve this target, a deeper understanding of their properties and conductivity mechanisms is needed. Herein, in a family of Al/Mg mixed metal ionic liquid-based electrolytes for secondary batteries, the ion-speciation, thermal behavior and long-range charge-migration processes is studied. It is revealed that the chemical compositions and temperature modulate the distribution of AlCl4− and Al2Cl7− species in the anionic nanoaggregates of materials. These modifications are responsible of the mobility of ions, which is studied in detail by means of broadband electrical spectroscopy and pulse-field-gradient NMR. Results yield a clear picture of the role of ion aggregates in the long-range charge-migration processes occurring in these electrolytes.