(140e) Alkyl Chain Length and Nanoconfinement Effects on Dynamics of Imidazolium-Based Ionic Liquids

Authors: 
Zhang, Y., Vanderbilt University
Otsi, N. C., Oak Ridge National Laboratory
Mamontov, E., Oak RIdge National Laboratory
Cummings, P. T., Vanderbilt University
Room-temperature ionic liquids (RTILs), due to their unique properties, such as wide electrochemical window and high thermal stability, are considered as excellent candidates as electrolytes for supercapacitors. While the high operating voltage window allows for a high energy density, the slow dynamics of RTILs may lead to a moderate power density, especially in the case of confinement. Understanding the constraints on the power density of supercapacitor based on nanoporous materials and RTILs is still limited.

In this work, molecular dynamics (MD) simulations were conducted to investigate the dynamics of a set of imidazolium-based RTILs with different side chain lengths. The effect of alkyl chain length is discussed by comparing the ion self-diffusion coefficients between different RTILs. The ion diffusivities are also compared with bulk values to evaluate the effects of nanoconfinment. Structural analysis of ions in bulk and confinement are made to further explain the effect of nanoconfinement. In addition, we rely on Quasi-elastic neutron scattering (QENS) experiments to validate the observed trends in MD simulations. This study helps to provide theoretical support for the design of energy storage devices that are better both in energy and power densities.