Toward New Ion Conductive Liquids via Ionic Liquids

Abstract

In the current era that it is strongly expected the SDGs would be achieved, electrolyte solutions in electrochemical devices and processes are being studied from dilute and concentrated solutions, through inorganic molten salts, deep eutectic solvents, and ionic liquids, to super‐concentrated solutions. Although concepts based on empirical laws such as the Walden rule and hydrodynamics such as the Stokes rule are still useful for ionic conduction in solution, it is expected that superionic conduction‐like mechanisms that are scarcely found in conventional electrolytes. Here, the authors′ recent results are described based on the local structure and speciation of ionic species in solution, focusing on protons and lithium ions.

Molecular Level Origin of Ion Dynamics in Highly Concentrated Electrolytes

“…However, these transport phenomena correspond to averaged dynamics on a relatively large scale, and as such, their correlation with microscopic behaviors on a molecular level (e.g., solvation/coordination structures, relaxation of the solvent structure, and the lifetimes of ion–ion/ion–solvent complexes) are obscured. Although several groups have investigated the above relationships by means of dielectric relaxation spectroscopy, − quasi-elastic neutron scattering, two-dimensional infrared spectroscopy, and nuclear magnetic resonance (NMR) spectroscopy based on the Bloembergen–Purcell–Pound theory, , it remains a challenge to obtain more direct information, particularly on the microscopic scale. In addition, current studies based on the use of molecular dynamics (MD) simulations endeavor to clarify the relationship between the molecular level behavior and the transport phenomena; − however, it is still a challenging issue being examined to date.…”