Modulation of cation diffusion by reversible supramolecular assemblies in ionic liquid based nanocomposites.

Ionic liquids (ILs) properties, such as high ionic conductivity under ambient conditions combined with non-toxicity and non-flammability, make them important materials for future technologies. Despite high ion conductivity desired for batteries application, the transport number of the cation in ILs is not sufficiently high to attain high power density batteries. Thus developing novel approaches directed towards improvement in transport properties of cation are desired to drive the application of ILs in energy storing devices. In this effort, by using various experimental techniques, we demonstrated that the strategy of mixing of ILs with ultra-small (1.8 nm in size) nanoparticles (NPs) resulted in melt-processable composites with improved transport number of the cation at room temperature. This significant enhancement in transport number was attributed to the specific chemistry of NPs exhibiting a weaker cation and stronger anion coordination at ambient temperature. At high temperature, significantly weakened NPs-anions association promoted a liquid-like behavior of composites, highlighting the melt-processability of these composites. These results show that designing a reversible dynamic non-covalent NPs-anions association controlled by the temperature may constitute an effective strategy to control the ion diffusion. Our studies provide fundamental insights into mechanisms driving the charge transport and offer practical guidance for the design of melt-processable composites with improved cation transport number at ambient conditions.