Temperature Dependency of Ion Transport in Highly Concentrated Li Salt/Sulfolane Electrolyte Solutions

Understanding the ion-conduction mechanism in concentrated electrolyte solutions of Li salts is helpful in designing electrolytes for advanced Li batteries. In certain highly concentrated electrolytes, the Li+ ion hopping/ligand exchange mechanism contributes to ionic conduction, and the transference number of Li+ becomes higher than 0.5, which mitigates the concentration polarization in Li batteries. However, details of the hopping mechanism remain unclear. In this study, we investigated the temperature dependence of the transport properties of Li salt/ sulfolane (SL) electrolytes. Using pulsed-field gradient nuclear magnetic resonance spectroscopy, we found that Li+ ion diffuses faster than SL and anion in highly concentrated electrolytes, suggesting that Li+-ion-hopping conduction occurs. The apparent activation energy (Ea) of the diffusivity of Li+ in highly concentrated electrolytes is slightly lower than Ea of the fluidity of liquid, which indicates that Li+-ion conduction is partially decoupled from the viscosity. The ratio of the actual molar conductivity to the calculated one based on the Nernst-Einstein relationship increases with decrease in temperature, leading to a lower Ea for ionic conduction compared to that of the fluidity and the ion diffusivity.

Automated summary

The study investigated the transport properties of Li salt/sulfolane (SL) electrolytes as a function of temperature. It was found that Li+ ion diffuses faster than other ions in highly concentrated electrolytes, indicating the occurrence of Li+-ion hopping conduction. The results provide important insights for designing electrolytes for advanced Li batteries.