Diffusion mechanisms in lithium based deep eutectic solvents – role of counterions

Deep eutectic solvents (DESs) have become ubiquitous in industrial and pharmaceutical applications owing to their ability to dissolve a wide range of metallic species and low vapour pressure. Lithium based DESs have also been studied widely to be adapted as a liquid electrolyte for secondary lithium ion batteries. Although a number of studies have shown the ability of DESs to function as successful electrolytes, a major setback has been the poor conductivity in these solvents compared to their organic counterparts. The microscopic diffusive processes in these solvents play a crucial role in their ionic conduction mechanism; therefore it is expedient to study them to gain a deeper understanding of the emergence of these bulk properties. QENS experiments was carried out on lithium based DESs with three different counterions – perchlorate, nitrate and bromide, using acetamide being the hydrogen bond donor in the DESs. This study clearly elucidates that the counterions play a crucial role in the modulating the long-range diffusion landscape of DESs. The findings of this study will be helpful in controlling the solvent transport properties by altering the nature of counterions in the system.