Ionic Liquid Electrolytes for Safer and More Reliable Sodium Battery Systems

Featured Application Sodium battery systems. Na+-conducting, binary electrolytic mixtures, based on 1-ethyl-3-methyl-imidazolium, trimethyl-butyl-ammonium, andN-alkyl-N-methyl-piperidinium ionic liquid (IL) families, were designed and investigated. The anions were selected among the per(fluoroalkylsulfonyl)imide families. Sodium bis(trifluoromethylsulfonyl)imide, NaTFSI, was selected as the salt. The NaTFSI-IL electrolytes, addressed to safer sodium battery systems, were studied and compared in terms of ionic conductivity and thermal stability as a function of the temperature, the nature of the anion and the cation aliphatic side chain length. Room temperature conductivities of interest for sodium batteries, i.e., largely overcoming 10(-4)or 10(-3)S cm(-1), are displayed. Similar conduction values are exhibited by the EMI-based samples even below -10 degrees C, making these electrolyte mixtures potentially appealing also for low temperature applications. The NaTFSI-IL electrolytes, with the exception of the FSI-ones, are found to be thermally stable up to 275 degrees C, depending on the nature of the cation and/or anion, thus extending their applicability above 100 degrees C and remarkably increasing the reliability and safety of the final device, especially in the case of prolonged overheating.